# Days between dates

Calculate the number of days between two dates.

Days between dates is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Date input should be of the form   YYYY-MM-DD.

Motivation

To demonstrate one of the numerous ways this can be done.

## 11l

```F parse_date(date)
R time:strptime(date, ‘%Y-%m-%d’)

V date1 = parse_date(‘2019-01-01’)
V date2 = parse_date(‘2019-09-30’)
print((date2 - date1).days())```
Output:
```272
```

## Action!

```INCLUDE "D2:REAL.ACT" ;from the Action! Tool Kit

TYPE Date=[CARD year BYTE month,day]

BYTE FUNC IsLeapYear(CARD y)
IF y MOD 100=0 THEN
IF y MOD 400=0 THEN RETURN (1)
ELSE RETURN (0) FI
FI
IF y MOD 4=0 THEN RETURN (1) FI
RETURN (0)

PROC DecodeDate(CHAR ARRAY s Date POINTER d)
BYTE ARRAY maxD=[0 31 28 31 30 31 30 31 31 30 31 30 31]
CHAR ARRAY tmp(5)
BYTE m

IF s(0)#10 THEN
Break()
FI
SCopyS(tmp,s,1,4) d.year=ValC(tmp)
SCopyS(tmp,s,6,7) d.month=ValB(tmp)
SCopyS(tmp,s,9,10) d.day=ValB(tmp)

IF d.year=0 OR d.month=0 OR d.month>12 OR d.day=0 THEN
Break()
FI
IF IsLeapYear(d.year) THEN
maxD(2)=29
ELSE
maxD(2)=28
FI
m=d.month
IF d.day>maxD(m) THEN
Break()
FI
RETURN

PROC DateToDays(Date POINTER d REAL POINTER res)
BYTE m
INT y,tmp1
REAL tmp2

m=(d.month+9) MOD 12
y=d.year-m/10
tmp1=y/4-y/100+y/400+(m*306+5)/10+(d.day-1)

IntToReal(365,res)
IntToReal(y,tmp2)
RealMult(res,tmp2,res)
IntToReal(tmp1,tmp2)
RETURN

PROC DiffDays(Date POINTER d1,d2 REAL POINTER diff)
REAL days1,days2

DateToDays(d1,days1)
DateToDays(d2,days2)
RealSub(days2,days1,diff)
RETURN

PROC Test(CHAR ARRAY s1,s2)
Date d1,d2
REAL diff

DecodeDate(s1,d1)
DecodeDate(s2,d2)
DiffDays(d1,d2,diff)
PrintF("%S .. %S -> ",s1,s2)
PrintRE(diff)
RETURN

PROC Main()
Put(125) PutE() ;clear the screen
Test("1995-11-21","1995-11-21")
Test("2019-01-01","2019-01-02")
Test("2019-01-02","2019-01-01")
Test("2019-01-01","2019-03-01")
Test("2020-01-01","2020-03-01")
Test("1902-01-01","1968-12-25")
Test("2090-01-01","2098-12-25")
Test("1902-01-01","2098-12-25")
RETURN```
Output:
```1995-11-21 .. 1995-11-21 -> 0
2019-01-01 .. 2019-01-02 -> 1
2019-01-02 .. 2019-01-01 -> -1
2019-01-01 .. 2019-03-01 -> 59
2020-01-01 .. 2020-03-01 -> 60
1902-01-01 .. 1968-12-25 -> 24465
2090-01-01 .. 2098-12-25 -> 3280
1902-01-01 .. 2098-12-25 -> 71947
```

```with Ada.Calendar;

with GNAT.Calendar.Time_IO;

procedure Days_Between_Dates is

function Days_Between (Lower_Date  : in Ada.Calendar.Time;
Higher_Date : in Ada.Calendar.Time) return Integer
is
Diff : constant Duration := Higher_Date - Lower_Date;
begin
return Integer (Diff / Day_Duration'Last);
end Days_Between;

procedure Put_Days_Between (Lower_Date  : in String;
Higher_Date : in String;
Comment     : in String)
is
use GNAT.Calendar.Time_IO;

Diff : constant Integer := Days_Between (Lower_Date  => Value (Lower_Date),
Higher_Date => Value (Higher_Date));
begin
Put ("Days between " & Lower_Date & " and " & Higher_Date & " is ");
Put (Diff, Width => 5);
Put (" days  --  ");
Put (Comment);
New_Line;
end Put_Days_Between;

begin
Put_Days_Between ("1995-11-21", "1995-11-21", "Identical dates");
Put_Days_Between ("2019-01-01", "2019-01-02", "Positive span");
Put_Days_Between ("2019-01-02", "2019-01-01", "Negative span");
Put_Days_Between ("2019-01-01", "2019-03-01", "Non-leap year");
Put_Days_Between ("2020-01-01", "2020-03-01", "Leap year");
Put_Days_Between ("1902-01-01", "1968-12-25", "Past");
Put_Days_Between ("2090-01-01", "2098-12-25", "Future");
Put_Days_Between ("1902-01-01", "2098-12-25", "Long span");
end Days_Between_Dates;
```
Output:
```Days between 1995-11-21 and 1995-11-21 is     0 days  --  Identical dates
Days between 2019-01-01 and 2019-01-02 is     1 days  --  Positive span
Days between 2019-01-02 and 2019-01-01 is    -1 days  --  Negative span
Days between 2019-01-01 and 2019-03-01 is    59 days  --  Non-leap year
Days between 2020-01-01 and 2020-03-01 is    60 days  --  Leap year
Days between 1902-01-01 and 1968-12-25 is 24465 days  --  Past
Days between 2090-01-01 and 2098-12-25 is  3280 days  --  Future
Days between 1902-01-01 and 2098-12-25 is 71947 days  --  Long span```

## AppleScript

```on daysBetweenDates(date1, date2)
considering numeric strings -- Allows for leading zeros having been omitted.
if (date1 = date2) then return date1 & " and " & date2 & " are the same date"
end considering

-- Get the components of each date.
set astid to AppleScript's text item delimiters
set AppleScript's text item delimiters to "-"
set {y1, m1, d1} to date1's text items
set {y2, m2, d2} to date2's text items
set AppleScript's text item delimiters to astid

-- Derive AppleScript date objects.
-- The best way to do this generally is to use the 'current date' function to obtain a date object
-- and then to set the properties of the result (or of a copy) to the required values.
-- The initial setting of the day values to 1 is to prevent overflow due to possibly
-- incompatible day and month values during the sequential setting of the properties.
-- The integer values set here are automatically coerced from the text values obtained above.
tell (current date) to set {its day, its year, its month, its day, its time, firstDate} to {1, y1, m1, d1, 0, it}
copy firstDate to secondDate
tell secondDate to set {its day, its year, its month, its day} to {1, y2, m2, d2}

-- Do the math.
set daysDifference to (firstDate - secondDate) div days

-- Format some output.
if (daysDifference > 0) then
return date1 & " comes " & daysDifference & " day" & item (((daysDifference is 1) as integer) + 1) of {"s", ""} & ¬
" after " & date2
else
return date1 & " comes " & -daysDifference & " day" & item (((daysDifference is -1) as integer) + 1) of {"s", ""} & ¬
" before " & date2
end if
end daysBetweenDates

return daysBetweenDates("2020-04-11", "2001-01-01") & linefeed & ¬
daysBetweenDates("2020-04-11", "2020-04-12") & linefeed & ¬
daysBetweenDates("2020-04-11", "2020-04-11")
```
Output:
```"2020-04-11 comes 7040 days after 2001-01-01
2020-04-11 comes 1 day before 2020-04-12
2020-04-11 and 2020-04-11 are the same date"```

Or, composing a function from reusable generics, and drawing on NSISO8601DateFormatter:

```use AppleScript version "2.4"
use framework "Foundation"

-- daysBetween :: String -> String -> Int
on daysBetween(iso8601From, iso8601To)
set midnight to "T00:00:00+00:00"
((dateFromISO8601(iso8601To & midnight) - ¬
dateFromISO8601(iso8601From & midnight)) / 86400) as integer
end daysBetween

-- dateFromISO8601 :: String -> Date
on dateFromISO8601(isoDateString)
set ca to current application
tell ca's NSISO8601DateFormatter's alloc's init()
set its formatOptions to ¬
(ca's NSISO8601DateFormatWithInternetDateTime as integer)
(its dateFromString:(isoDateString)) as date
end tell
end dateFromISO8601

---------------------------TEST----------------------------
on run
script test
on |λ|(ab)
set {a, b} to ab
set delta to daysBetween(a, b)
(a & " -> " & b & " -> " & ¬
justifyRight(5, space, delta as string)) & ¬
pluralize(delta, " day")
end |λ|
end script

unlines(map(test, {¬
{"2020-04-11", "2001-01-01"}, ¬
{"2020-04-11", "2020-04-12"}, ¬
{"2020-04-11", "2020-04-11"}, ¬
{"2019-01-01", "2019-09-30"}}))
end run

--------------------GENERIC FUNCTIONS ---------------------

-- Absolute value.
-- abs :: Num -> Num
on abs(x)
if 0 > x then
-x
else
x
end if
end abs

-- justifyRight :: Int -> Char -> String -> String
on justifyRight(n, cFiller, strText)
if n > length of strText then
text -n thru -1 of ((replicate(n, cFiller) as text) & strText)
else
strText
end if
end justifyRight

-- map :: (a -> b) -> [a] -> [b]
on map(f, xs)
-- The list obtained by applying f
-- to each element of xs.
tell mReturn(f)
set lng to length of xs
set lst to {}
repeat with i from 1 to lng
set end of lst to |λ|(item i of xs, i, xs)
end repeat
return lst
end tell
end map

-- mReturn :: First-class m => (a -> b) -> m (a -> b)
on mReturn(f)
-- 2nd class handler function lifted into 1st class script wrapper.
if script is class of f then
f
else
script
property |λ| : f
end script
end if
end mReturn

-- pluralize :: Int -> String -> String
on pluralize(n, s)
set m to abs(n)
if 0 = m or 2 ≤ m then
s & "s"
else
s
end if
end pluralize

-- replicate :: Int -> String -> String
on replicate(n, s)
set out to ""
if n < 1 then return out
set dbl to s

repeat while (n > 1)
if (n mod 2) > 0 then set out to out & dbl
set n to (n div 2)
set dbl to (dbl & dbl)
end repeat
return out & dbl
end replicate

-- unlines :: [String] -> String
on unlines(xs)
-- A single string formed by the intercalation
-- of a list of strings with the newline character.
set {dlm, my text item delimiters} to ¬
{my text item delimiters, linefeed}
set str to xs as text
set my text item delimiters to dlm
str
end unlines
```
Output:
```2020-04-11 -> 2001-01-01 -> -7040 days
2020-04-11 -> 2020-04-12 ->     1 day
2020-04-11 -> 2020-04-11 ->     0 days
2019-01-01 -> 2019-09-30 ->   272 days```

## Arturo

Translation of: Ruby
```daysBetweenDates: function [startDate, endDate][
a: to :date.format: "dd/MM/yyyy" startDate
b: to :date.format: "dd/MM/yyyy" endDate

return abs b\days - a\days
]

print [
"days between the two dates:"
daysBetweenDates "01/01/2019" "19/10/2019"
]
```
Output:
`days between the two dates: 291`

## AutoHotkey

```db =
(
1995-11-21|1995-11-21
2019-01-01|2019-01-02
2019-01-02|2019-01-01
2019-01-01|2019-03-01
2020-01-01|2020-03-01
1902-01-01|1968-12-25
2090-01-01|2098-12-25
1902-01-01|2098-12-25
)

for i, line in StrSplit(db, "`n", "`r"){
D := StrSplit(line, "|")
result .= "Days between " D.1 " and " D.2 "  :  " Days_between(D.1, D.2) " Day(s)`n"
}
MsgBox, 262144, , % result
return

Days_between(D1, D2){
D1 := RegExReplace(D1, "\D")
D2 := RegExReplace(D2, "\D")
EnvSub, D2, % D1, days
return D2
}
```
Output:
```Days between 1995-11-21 and 1995-11-21  :  0 Day(s)
Days between 2019-01-01 and 2019-01-02  :  1 Day(s)
Days between 2019-01-02 and 2019-01-01  :  -1 Day(s)
Days between 2019-01-01 and 2019-03-01  :  59 Day(s)
Days between 2020-01-01 and 2020-03-01  :  60 Day(s)
Days between 1902-01-01 and 1968-12-25  :  24465 Day(s)
Days between 2090-01-01 and 2098-12-25  :  3280 Day(s)
Days between 1902-01-01 and 2098-12-25  :  71947 Day(s)```

## AWK

```# syntax: GAWK -f DAYS_BETWEEN_DATES.AWK
BEGIN {
regexp = "^....-..-..\$" # YYYY-MM-DD
main("1969-12-31","1970-01-01","builtin has bad POSIX start date")
main("1970-01-01","2038-01-19","builtin has bad POSIX stop date")
main("1970-01-01","2019-10-02","format OK")
main("1970-01-01","2019/10/02","format NG")
main("1995-11-21","1995-11-21","identical dates")
main("2019-01-01","2019-01-02","positive date")
main("2019-01-02","2019-01-01","negative date")
main("2019-01-01","2019-03-01","non-leap year")
main("2020-01-01","2020-03-01","leap year")
exit(0)
}
function main(date1,date2,comment,  d1,d2,diff) {
printf("\t%s\n",comment)
d1 = days_builtin(date1)
d2 = days_builtin(date2)
diff = (d1 == "" || d2 == "") ? "error" : d2-d1
printf("builtin %10s to %10s = %s\n",date1,date2,diff)
d1 = days_generic(date1)
d2 = days_generic(date2)
diff = (d1 == "" || d2 == "") ? "error" : d2-d1
printf("generic %10s to %10s = %s\n",date1,date2,diff)
}
function days_builtin(ymd) { # use gawk builtin
if (ymd !~ regexp) { return("") }
if (ymd < "1970-01-01" || ymd > "2038-01-18") { return("") } # outside POSIX range
gsub(/-/," ",ymd)
return(int(mktime(sprintf("%s 0 0 0",ymd)) / (60*60*24)))
}
function days_generic(ymd,  d,m,y,result) { # use Python formula
if (ymd !~ regexp) { return("") }
y = substr(ymd,1,4)
m = substr(ymd,6,2)
d = substr(ymd,9,2)
m = (m + 9) % 12
y = int(y - int(m/10))
result = 365*y + int(y/4) - int(y/100) + int(y/400) + int((m*306+5)/10) + (d-1)
return(result)
}
```
Output:
```    builtin has bad POSIX start date
builtin 1969-12-31 to 1970-01-01 = error
generic 1969-12-31 to 1970-01-01 = 1
builtin has bad POSIX stop date
builtin 1970-01-01 to 2038-01-19 = error
generic 1970-01-01 to 2038-01-19 = 24855
format OK
builtin 1970-01-01 to 2019-10-02 = 18171
generic 1970-01-01 to 2019-10-02 = 18171
format NG
builtin 1970-01-01 to 2019/10/02 = error
generic 1970-01-01 to 2019/10/02 = error
identical dates
builtin 1995-11-21 to 1995-11-21 = 0
generic 1995-11-21 to 1995-11-21 = 0
positive date
builtin 2019-01-01 to 2019-01-02 = 1
generic 2019-01-01 to 2019-01-02 = 1
negative date
builtin 2019-01-02 to 2019-01-01 = -1
generic 2019-01-02 to 2019-01-01 = -1
non-leap year
builtin 2019-01-01 to 2019-03-01 = 59
generic 2019-01-01 to 2019-03-01 = 59
leap year
builtin 2020-01-01 to 2020-03-01 = 60
generic 2020-01-01 to 2020-03-01 = 60
```

## C

```#include<stdbool.h>
#include<string.h>
#include<stdio.h>

typedef struct{
int year, month, day;
}date;

date extractDate(char* str){
return (date){.year = 1000 * (str[0]-'0') + 100 * (str[1]-'0') + 10 * (str[2]-'0') + (str[3]-'0'), .month = 10*(str[5]-'0') + (str[6]-'0'), .day = 10*(str[8]-'0') + (str[9]-'0')};
}

bool isValidDate(char* str){
date newDate;

if(strlen(str)!=10 && str[4]!='-' && str[7]!='-'){
return false;
}

newDate = extractDate(str);

if(newDate.year<=0 || newDate.month<=0 || newDate.day<=0 || newDate.month>12 || (newDate.month==2 && newDate.day>29) ||
((newDate.month==1 || newDate.month==3 || newDate.month==5 || newDate.month==7 || newDate.month==8 || newDate.month==10 || newDate.month==12) && newDate.day>31) ||
newDate.day>30 || (newDate.year%4==0 && newDate.month==2 && newDate.month>28)){
return false;
}

return true;
}

int diffDays(date date1,date date2){
int days1, days2;

date1.month = (date1.month + 9)%12;
date1.year = date1.year - date1.month/10;

date2.month = (date2.month + 9)%12;
date2.year = date2.year - date2.month/10;

days1 = 365*date1.year + date1.year/4 - date1.year/100 + date1.year/400 + (date1.month*306 + 5)/10 + ( date1.day - 1 );
days2 = 365*date2.year + date2.year/4 - date2.year/100 + date2.year/400 + (date2.month*306 + 5)/10 + ( date2.day - 1 );

return days2 - days1;
}

int main(int argc,char** argv)
{
if(argc!=3){
return printf("Usage : %s <yyyy-mm-dd> <yyyy-mm-dd>",argv[0]);
}

if(isValidDate(argv[1])&&isValidDate(argv[2]) == false){
return printf("Dates are invalid.\n");
}

printf("Days Difference : %d\n", diffDays(extractDate(argv[1]),extractDate(argv[2])));

return 0;
}
```

Output :

```abhishek_ghosh@Azure:~/doodles\$ ./a.out 2019-01-01 2019-12-02
Days Difference : 335
```

## BQN

The `date` namespace is taken from bqn-libs. `DBw` is the final function which calculates the proper difference between two date strings.

```DivMod ← ⌊∘÷˜ ⋈ |
date ← {
o ← 719469
y ← 365.25
dur ← ⟨(100×y)-0.75,    y, 30.6⟩
off ← ⟨o-0.25,       0.75, 0.41⟩

From ⇐ {
y‿m‿d ← 𝕩
f ← 0 > m -↩ 3
(d-o) +´ ⌊ off +⌾(¯1⊸⊑) dur × (100 DivMod y-f) ∾ ⟨m+12×f⟩
}
To ⇐ {
t←𝕩
c‿y‿m ← dur { d‿m ← 𝕨 DivMod 𝕩+t ⋄ t↩⌊m ⋄ d }¨ off
m -↩ 12×10≤m
⟨(100×c)+y+m<0, 3+m, 1+t⟩
}
}
Split←(⊢-˜+`×¬)∘=⊔⊢
ToI←10⊸×⊸+˜´∘⌽-⟜'0'

S2D←ToI¨ '-'⊸Split
DBw ← -○(date.From S2D)```
```  "2019-09-30" DBw "2019-01-01"
272```

## C++

Translation of: c
```#include <iomanip>
#include <iostream>

class Date {
private:
int year, month, day;

public:
Date(std::string str) {
if (isValidDate(str)) {
year = atoi(&str[0]);
month = atoi(&str[5]);
day = atoi(&str[8]);
} else {
throw std::exception("Invalid date");
}
}

int getYear() {
return year;
}

int getMonth() {
return month;
}

int getDay() {
return day;
}

// YYYY-MM-DD
static bool isValidDate(std::string str) {
if (str.length() != 10 || str[4] != '-' || str[7] != '-') {
return false;
}

if (!isdigit(str[0]) || !isdigit(str[1]) || !isdigit(str[2]) || !isdigit(str[3])) {
return false; // the year is not valid
}
if (!isdigit(str[5]) || !isdigit(str[6])) {
return false; // the month is not valid
}
if (!isdigit(str[8]) || !isdigit(str[9])) {
return false; // the day is not valid
}

int year = atoi(&str[0]);
int month = atoi(&str[5]);
int day = atoi(&str[8]);

// quick checks
if (year <= 0 || month <= 0 || day <= 0) {
return false;
}
if (month > 12) {
return false;
}

switch (month) {
case 2:
if (day > 29) {
return false;
}
if (!isLeapYear(year) && day == 29) {
return false;
}
break;
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
if (day > 31) {
return false;
}
break;
default:
if (day > 30) {
return false;
}
break;
}

return true;
}

static bool isLeapYear(int year) {
if (year > 1582) {
return ((year % 4 == 0) && (year % 100 > 0))
|| (year % 400 == 0);
}
if (year > 10) {
return year % 4 == 0;
}
// not bothering with earlier leap years
return false;
}

friend std::ostream &operator<<(std::ostream &, Date &);
};

std::ostream &operator<<(std::ostream &os, Date &d) {
os << std::setfill('0') << std::setw(4) << d.year << '-';
os << std::setfill('0') << std::setw(2) << d.month << '-';
os << std::setfill('0') << std::setw(2) << d.day;
return os;
}

int diffDays(Date date1, Date date2) {
int d1m = (date1.getMonth() + 9) % 12;
int d1y = date1.getYear() - d1m / 10;

int d2m = (date2.getMonth() + 9) % 12;
int d2y = date2.getYear() - d2m / 10;

int days1 = 365 * d1y + d1y / 4 - d1y / 100 + d1y / 400 + (d1m * 306 + 5) / 10 + (date1.getDay() - 1);
int days2 = 365 * d2y + d2y / 4 - d2y / 100 + d2y / 400 + (d2m * 306 + 5) / 10 + (date2.getDay() - 1);

return days2 - days1;
}

int main() {
std::string ds1 = "2019-01-01";
std::string ds2 = "2019-12-02";

if (Date::isValidDate(ds1) && Date::isValidDate(ds2)) {
Date d1(ds1);
Date d2(ds2);
std::cout << "Days difference : " << diffDays(d1, d2);
} else {
std::cout << "Dates are invalid.\n";
}

return 0;
}
```
Output:
`Days difference : 335`

### Alternative using Boost

Library: Boost
```#include <cstdlib>
#include <iostream>
#include <boost/date_time/gregorian/gregorian.hpp>

int main(int argc, char** argv) {
using namespace boost::gregorian;
if (argc != 3) {
std::cerr << "usage: " << argv[0] << " start-date end-date\n";
return EXIT_FAILURE;
}
try {
date start_date(from_simple_string(argv[1]));
date end_date(from_simple_string(argv[2]));
std::cout << end_date - start_date << '\n';
} catch (const std::exception& ex) {
std::cerr << ex.what() << '\n';
return EXIT_FAILURE;
}
return EXIT_SUCCESS;
}
```
Output:
```./days_between_dates 2020-01-01 2020-09-06
249
```

## C#

```using System;
using System.Globalization;

public class Program
{
public static void Main() => WriteLine(DateDiff("1970-01-01", "2019-10-18"));

public static int DateDiff(string d1, string d2) {
var a = DateTime.ParseExact(d1, "yyyy-MM-dd", CultureInfo.InvariantCulture);
var b = DateTime.ParseExact(d2, "yyyy-MM-dd", CultureInfo.InvariantCulture);
return (int)(b - a).TotalDays;
}
}
```
Output:
```18187
```

## COBOL

Works with: GnuCOBOL
```COBOL *> days-between
*> Tectonics: cobc -xj days-between.cob

identification division.
program-id. days-between.

procedure division.
compute tally =
function integer-of-formatted-date('YYYY-MM-DD', '2019-11-24')
-
function integer-of-formatted-date('YYYY-MM-DD', '2000-01-01')
display tally

compute tally =
function integer-of-formatted-date('YYYYMMDD', '20191124')
-
function integer-of-formatted-date('YYYYMMDD', '20000101')
display tally

goback.
end program days-between.
```
Output:
```prompt\$ cobc -xj days-between-dates.cob
07267
07267```

## Commodore BASIC

```100 REM ===============================
110 REM DAYS BETWEEN 2 DATES
120 REM
130 REM CONVERT FROM TEXT TO PRG
140 REM USING C64LIST.EXE V3.5
150 REM COMMAND LINE UTILITY ON WINDOWS
160 REM
170 REM V1, 2021-10-09, ALVALONGO
180 REM ===============================
190 REM
200 REM INSPIRED BY THE PYTHON VERSION
210 REM OF THE ALGORITHM
220 REM AND THE DISCUSSION AT
230 REM HTTPS://STACKOVERFLOW.COM/QUESTIONS/12862226
240 REM /THE-IMPLEMENTATION-OF-CALCULATING-THE-NUMBER-OF-DAYS-BETWEEN-2-DATES
250 REM ===============================
260 :
1000 REM INIT ============================
1010 PRINT CHR\$(147);:REM CLEAR SCREEN
1020 PRINT CHR\$(5);:REM INK WHITE COLOR
1030 POKE 53280,3:REM BORDER COLOR CYAN
1040 POKE 53281,14:REM BACKGROUND COLOR BLUE
1050 :
1100 REM MAIN ==========================
1110 PRINT "          DAYS BETWEEN 2 DATES"
1120 PRINT
1130 INPUT "FIRST DATE, YEAR";Y1
1140 INPUT "MONTH=";M1
1150 INPUT "DAY  =";D1
1160 INPUT "SECOND DATE, YEAR";Y2
1170 INPUT "MONTH=";M2
1180 INPUT "DAY  =";D2
1190 Y=Y1:M=M1:D=D1:GOSUB 9000:G1=G
1200 Y=Y2:M=M2:D=D2:GOSUB 9000:G2=G
1210 DI=ABS(G2-G1)
1220 PRINT "DAYS=";DI
1230 GET K\$:IF K\$="" THEN 1230
1240 PRINT
1250 GOTO 1120
1260 END
1270 :
9000 REM GREGORIAN ======================
9010 REM TRANSFORM A DATE INTO A DAY NUMBER IN THE GREGORIAN CALENDAR
9020 REM INPUT PARAMETERS: Y IS YEAR
9030 REM M IS MONTH
9040 REM D IS DAY
9050 N=(M+9)-INT((M+9)/12)*12
9060 W=Y-INT(N/10)
9070 G=365*W+INT(W/4)-INT(W/100)+INT(W/400)
9080 G=G+INT((N*306+5)/10)+(D-1)
9090 RETURN
```

## D

```import std.datetime.date;
import std.stdio;

void main() {
auto fromDate = Date.fromISOExtString("2019-01-01");
auto toDate = Date.fromISOExtString("2019-10-07");
auto diff = toDate - fromDate;
writeln("Number of days between ", fromDate, " and ", toDate, ": ", diff.total!"days");
}
```
Output:
`Number of days between 2019-Jan-01 and 2019-Oct-07: 279`

## Delphi

Translation of: C#
```program Days_between_dates;

{\$APPTYPE CONSOLE}

uses
System.SysUtils;

function CreateFormat(fmt: string; Delimiter: Char): TFormatSettings;
begin
Result := TFormatSettings.Create();
with Result do
begin
DateSeparator := Delimiter;
ShortDateFormat := fmt;
end;
end;

function DaysBetween(Date1, Date2: string): Integer;
var
dt1, dt2: TDateTime;
fmt: TFormatSettings;
begin
fmt := CreateFormat('yyyy-mm-dd', '-');
dt1 := StrToDate(Date1, fmt);
dt2 := StrToDate(Date2, fmt);
Result := Trunc(dt2 - dt1);
end;

begin
Writeln(DaysBetween('1970-01-01', '2019-10-18'));
end.
```
Output:
`18187`

## Erlang

```-module(daysbetween).
-export([between/2,dateToInts/2]).

% Return Year or Month or Date from datestring
dateToInts(String, POS) ->
list_to_integer( lists:nth( POS, string:tokens(String, "-") ) ).

% Alternative form of above
% dateToInts(String,POS) ->
%   list_to_integer( lists:nth( POS, re:split(String ,"-", [{return,list},trim]) ) ).

% Return the number of days between dates formatted "2019-09-30"
between(DateOne,DateTwo) ->
L = [1,2,3],
[Y1,M1,D1] =  [ dateToInts(DateOne,X) || X <- L],
[Y2,M2,D2] =  [ dateToInts(DateTwo,X) || X <- L],
GregOne = calendar:date_to_gregorian_days(Y1,M1,D1),
GregTwo = calendar:date_to_gregorian_days(Y2,M2,D2),
GregTwo - GregOne.
```
Output:

erlang shell:

```30> c(daysbetween).
c(daysbetween).
{ok,daysbetween}
31> daysbetween:between("2019-01-01", "2019-09-30").
daysbetween:between("2019-01-01", "2019-09-30").
272
```

## Excel

### LAMBDA

Excel dates are numbers counting days since the start of January 1900, and arithmetic operations can be applied to them directly.

(Unless entered as strings, they differ from other numbers only in the display format applied to the containing cell).

The lambda expression below maps over an array of date strings, defining a new array of the differences, in units of one day, between today's date and those earlier dates.

Output:

The formula in cell B2 defines the array of day counts which populate the range B2:B5

 =LAMBDA(dateString, TODAY() - DATEVALUE(dateString) )(C2#) fx A B C D 1 Difference in days Earlier date Today 2 39020 1914-07-28 2021-05-27 3 37088 1919-11-11 4 29916 1939-07-01 5 27661 1945-09-02

Alternatively, we can express the same mapping over the whole C2# array by directly writing:

 = TODAY() - DATEVALUE(C2#) fx A B C D 1 Difference in days Earlier date Today 2 39020 1914-07-28 2021-05-27 3 37088 1919-11-11 4 29916 1939-07-01 5 27661 1945-09-02

## F#

```// Days between dates: Nigel Galloway. June 3rd., 2021
let n,g=System.DateTime.Parse("1792-9-22"),System.DateTime.Parse("1805-12-31")
printfn "There are %d days between %d-%d-%d and %d-%d-%d" (g-n).Days n.Year n.Month n.Day g.Year g.Month g.Day
```
Output:
```There are 4847 days between 1792-9-22 and 1805-12-31
```

## Factor

Factor supports the addition and subtraction of timestamps and durations with the `time+` and `time-` words.

```USING: calendar calendar.parser kernel math prettyprint ;

: days-between ( ymd-str ymd-str -- n )
[ ymd>timestamp ] bi@ time- duration>days abs ;

"2019-01-01" "2019-09-30" days-between .
"2016-01-01" "2016-09-30" days-between .  ! leap year
```
Output:
```272
273
```

## FreeBASIC

```Dim Shared As Integer M, Y, D
Dim As Integer Y1, M1, D1, Y2, M2, D2, G1, G2
Dim As String DaysBetween(7, 2) = {{"1902-01-01","1968-12-25"}, _
{"2019-01-01","2019-01-02"}, {"2019-01-02","2019-01-01"}, _
{"2019-01-01","2019-03-01"}, {"2020-01-01","2020-03-01"}, _
{"1995-11-21","1995-11-21"}, {"2090-01-01","2098-12-25"}}

Function Gregorian() As Integer
Dim As Integer N = (M+9) - Int((M+9)/12) * 12
Dim As Integer W = Y - Int(N/10)
Dim As Integer G = 365 * W + Int(W/4) - Int(W/100) + Int(W/400)
G += Int((N*306+5)/10)+(D-1)
Return G
End Function

For n As Integer = 0 To Ubound(DaysBetween)-1
Y1 = Val(Left(DaysBetween(n,0),4))
M1 = Val(Mid(DaysBetween(n,0),6,2))
D1 = Val(Right(DaysBetween(n,0),2))
Y2 = Val(Mid(DaysBetween(n,1),1,4))
M2 = Val(Mid(DaysBetween(n,1),6,2))
D2 = Val(Mid(DaysBetween(n,1),9,2))
Y = Y1 : M = M1 : D = D1 : G1 = Gregorian
Y = Y2 : M = M2 : D = D2 : G2 = Gregorian
Print "Days between "; DaysBetween(n,0); " and "; DaysBetween(n,1); " is ";
Print Using "##### days"; (G2-G1)
Next n
Sleep
```
Output:
```Days between 1902-01-01 and 1968-12-25 is 24465 days
Days between 2019-01-01 and 2019-01-02 is     1 days
Days between 2019-01-02 and 2019-01-01 is    -1 days
Days between 2019-01-01 and 2019-03-01 is    59 days
Days between 2020-01-01 and 2020-03-01 is    60 days
Days between 1995-11-21 and 1995-11-21 is     0 days
Days between 2090-01-01 and 2098-12-25 is  3280 days
```

## Frink

Frink handles dates and intervals between dates robustly, including time zones. The sample below could use `minutes` or `seconds` instead of `days`.

Frink can even track leap seconds as they are added to the calendar if desired. The code `d1-d2` in the sample below could be replaced by `subtractLeap[d1,d2]` to obtain exact counts of seconds between dates.

See Frink's Date/Time Handling documentation to see how easy it is to work with dates, times, timezones, calendrical systems, and even leap seconds correctly and easily.

```d1 = # 2020-12-25 #
d2 = # 2020-12-06 #
println[d1-d2 -> days]```
Output:
```19
```

## Fōrmulæ

Fōrmulæ programs are not textual, visualization/edition of programs is done showing/manipulating structures but not text. Moreover, there can be multiple visual representations of the same program. Even though it is possible to have textual representation —i.e. XML, JSON— they are intended for storage and transfer purposes more than visualization and edition.

Programs in Fōrmulæ are created/edited online in its website, However they run on execution servers. By default remote servers are used, but they are limited in memory and processing power, since they are intended for demonstration and casual use. A local server can be downloaded and installed, it has no limitations (it runs in your own computer). Because of that, example programs can be fully visualized and edited, but some of them will not run if they require a moderate or heavy computation/memory resources, and no local server is being used.

## Go

```package main

import (
"fmt"
"log"
"time"
)

const layout = "2006-01-02" // template for time.Parse

// Parameters assumed to be in YYYY-MM-DD format.
func daysBetween(date1, date2 string) int {
t1, err := time.Parse(layout, date1)
check(err)
t2, err := time.Parse(layout, date2)
check(err)
days := int(t1.Sub(t2).Hours() / 24)
if days < 0 {
days = -days
}
return days
}

func check(err error) {
if err != nil {
log.Fatal(err)
}
}

func main() {
date1, date2 := "2019-01-01", "2019-09-30"
days := daysBetween(date1, date2)
fmt.Printf("There are %d days between %s and %s\n", days, date1, date2)

date1, date2 = "2015-12-31", "2016-09-30"
days = daysBetween(date1, date2)
fmt.Printf("There are %d days between %s and %s\n", days, date1, date2)
}
```
Output:
```There are 272 days between 2019-01-01 and 2019-09-30
There are 274 days between 2015-12-31 and 2016-09-30
```

## Groovy

Translation of: Kotlin
Translation of: Java
```import java.time.LocalDate

def fromDate = LocalDate.parse("2019-01-01")
def toDate = LocalDate.parse("2019-10-19")
def diff = fromDate - toDate
println "Number of days between \${fromDate} and \${toDate}: \${diff}"
```
Output:
`Number of days between 2019-01-01 and 2019-10-19: 291`

```import Data.Time (Day)
import Data.Time.Calendar (diffDays)
import Data.Time.Format (parseTimeM,defaultTimeLocale)

main = do

task :: String -> String -> String
task xs ys =  "There are " ++ (show \$ betweenDays xs ys) ++ " days between " ++ xs ++ " and " ++ ys ++ "."

betweenDays :: String -> String -> Integer
betweenDays date1 date2 = go (stringToDay date1) (stringToDay date2)
where
go (Just x) (Just y) = diffDays y x
go Nothing _ = error "Exception: Bad format first date"
go _ Nothing = error "Exception: Bad format second date"

stringToDay :: String -> Maybe Day
stringToDay date = parseTimeM True defaultTimeLocale "%Y-%-m-%-d" date
```
Output:
```There are 272 days between 2019-01-01 and 2019-09-30.
There are 274 days between 2015-12-31 and 2016-09-30.```

Or, composing rather than raising errors:

```import Data.Time (Day)
import Data.Time.Calendar (diffDays)
import Data.Time.Format (defaultTimeLocale, parseTimeM)

-------------------- DAYS BETWEEN DATES ------------------

daysBetween :: String -> String -> Maybe Integer
daysBetween s1 s2 =
dayFromString s2
>>= \d2 -> diffDays d2 <\$> dayFromString s1

dayFromString :: String -> Maybe Day
dayFromString =
parseTimeM
True
defaultTimeLocale
"%Y-%-m-%-d"

--------------------------- TEST -------------------------
main :: IO ()
main =
mapM_
(putStrLn . uncurry showDateDiff)
[ ("2019-01-01", "2019-09-30"),
("2015-12-31", "2016-09-30")
]

showDateDiff :: String -> String -> String
showDateDiff s1 s2 =
maybe
(unlines ["Unparseable as date string pair:", s1, s2])
( \n ->
concat
[ "There are ",
show n,
" days between ",
s1,
" and ",
s2,
"."
]
)
\$ daysBetween s1 s2
```
Output:
```There are 272 days between 2019-01-01 and 2019-09-30.
There are 274 days between 2015-12-31 and 2016-09-30.```

## J

```   require'~addons/types/datetime/datetime.ijs'
2021 03 16 daysDiff 1960 05 04
22231

vectorize=: [: evaluate hyphen_to_space
hyphen_to_space=: (=&'-')`(,:&' ')}
evaluate=: ".
but_first=: &

'2021-03-16' daysDiff but_first vectorize  '1960-05-04'
22231
```

## Java

Translation of: Kotlin
```import java.time.LocalDate;
import java.time.temporal.ChronoUnit;

public class DaysBetweenDates {
public static void main(String[] args) {
LocalDate fromDate = LocalDate.parse("2019-01-01");
LocalDate toDate = LocalDate.parse("2019-10-19");
long diff = ChronoUnit.DAYS.between(fromDate, toDate);
System.out.printf("Number of days between %s and %s: %d\n", fromDate, toDate, diff);
}
}
```
Output:
`Number of days between 2019-01-01 and 2019-10-19: 291`

## JavaScript

```const timeRatio = 1000 * 60 * 60 * 24;
var floor = Math.floor, abs = Math.abs;
var daysBetween = (d1, d2) => floor(abs(new Date(d1) - new Date(d2)) / timeRatio);

console.log('Days between 2021-10-27 and 2020-03-03: %s', daysBetween('2021-10-27', '2020-03-03'));
```
Output:
`Days between 2021-10-27 and 2020-03-03: 603`

## jq

Works with: jq

Works with gojq, the Go implementation of jq

Two solutions are provided: the first uses jq's built-ins and is very brief. The second starts from first principles, and is of potential interest because of the various generic functions that are provided. The output is the same in both cases.

### Using jq's built-ins

```def days_between(yyyymmddBefore; yyyymmddAfter):
(yyyymmddBefore | strptime("%Y-%m-%d") | mktime) as \$before
| (yyyymmddAfter | strptime("%Y-%m-%d") | mktime) as \$after
# leap seconds are always inserted
| ((\$after - \$before) / (24*60*60) | floor) ;

def prolog: "In the following, if the dates are not the same,",
"the \"from\" date is included in the count of days, but the \"to\" date is not.\n",
"If the first date is later than the second date, the count of days is negated.";

def dates:
["1995-11-21", "1995-11-21"],
["2019-01-01", "2019-01-02"],
["2019-01-02", "2019-01-01"],
["2019-01-01", "2019-03-01"],
["2020-01-01", "2020-03-01"],
["1902-01-01", "1968-12-25"],
["2090-01-01", "2098-12-25"],
["1902-01-01", "2098-12-25"],
["1970-01-01", "2019-10-18"],
["2019-03-29", "2029-03-29"],
["2020-02-29", "2020-03-01"] ;

prolog,
(dates | "The number of days from \(.[0]) until \(.[1]) is \(days_between(.[0]; .[1] ))")
;

Output:
```In the following, if the dates are not the same,
the "from" date is included in the count of days, but the "to" date is not.

If the first date is later than the second date, the count of days is negated.
The number of days from 1995-11-21 until 1995-11-21 is 0
The number of days from 2019-01-01 until 2019-01-02 is 1
The number of days from 2019-01-02 until 2019-01-01 is -1
The number of days from 2019-01-01 until 2019-03-01 is 59
The number of days from 2020-01-01 until 2020-03-01 is 60
The number of days from 1902-01-01 until 1968-12-25 is 24465
The number of days from 2090-01-01 until 2098-12-25 is 3280
The number of days from 1902-01-01 until 2098-12-25 is 71947
The number of days from 1970-01-01 until 2019-10-18 is 18187
The number of days from 2019-03-29 until 2029-03-29 is 3653
The number of days from 2020-02-29 until 2020-03-01 is 1
```

### From first principles

```# In general, dates should be valid Julian dates on or after Jan 1, 0001, but
# for the most part, this is not checked, in part because some
# computations based on ostensibly invalid dates do produce useful
# results, e.g. days(2000; 1; 1) computes the number of days from Jan 1, 0001
# up to and including Jan 1, 2000 whereas days(2000; 1; 0) excludes Jan 1, 2000.

# Output: the number of days from and including Jan 1, 0001,
# up to but excluding Jan 1 in the year \$y for \$y >= 1
def days_before:
if . < 1
then "The input to days_before should be a positive integer, not \(.)"|error
else (. - 1 | floor) as \$y
| \$y*365 + ((\$y/4)|floor) - ((\$y/100)|floor) + ((\$y/400)|floor)
end;

def isLeapYear:
.%4 == 0 and (.%100 != 0 or .%400 == 0);

# The day of the year (Jan 1 is 1)
def day_of_year(\$y; \$m; \$d):
def diy: [0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365];
def diy2: [0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366];
\$d + if (\$y|isLeapYear) then diy2[\$m-1] else diy[\$m-1] end;

# Output: the number of days from Jan 1, 0001 to the specified date, inclusive.
def days(\$y; \$m; \$d):
(\$y | days_before) + day_of_year(\$y; \$m; \$d);

# Output: the signed difference in the "days" values of the two dates.
# If the first specified date is later than the second specified date,
# then the result is the number of days from and including the earlier date,
# up to but excluding the later date.
def days_between(Year; Month; Day; laterYear; laterMonth; laterDay):
days(laterYear; laterMonth; laterDay) -
days(Year; Month; Day);

# Dates in yyyy-mm-dd format or as a numeric array [y,m,d]
def days_between(date; later):
def toa: if type == "string" then split("-") | map(tonumber) else . end;
(later  | toa) as \$later
| (date | toa) as \$date
| days_between(\$date[0]; \$date[1]; \$date[2]; \$later[0]; \$later[1]; \$later[2]);```

As above.

Output:

Same as above.

## Julia

```using Dates

@show Day(DateTime("2019-09-30") - DateTime("2019-01-01"))

@show Day(DateTime("2019-03-01") - DateTime("2019-02-01"))

@show Day(DateTime("2020-03-01") - DateTime("2020-02-01"))

@show Day(DateTime("2029-03-29") - DateTime("2019-03-29"))
```
Output:
```Day(DateTime("2019-09-30") - DateTime("2019-01-01")) = 272 days
Day(DateTime("2019-03-01") - DateTime("2019-02-01")) = 28 days
Day(DateTime("2020-03-01") - DateTime("2020-02-01")) = 29 days
Day(DateTime("2029-03-29") - DateTime("2019-03-29")) = 3653 days
```

## Kotlin

```import java.time.LocalDate
import java.time.temporal.ChronoUnit

fun main() {
val fromDate = LocalDate.parse("2019-01-01")
val toDate = LocalDate.parse("2019-10-19")
val diff = ChronoUnit.DAYS.between(fromDate, toDate)
println("Number of days between \$fromDate and \$toDate: \$diff")
}
```
Output:
`Number of days between 2019-01-01 and 2019-10-19: 291`

## Lua

This uses os.difftime to compare two Epoch times. Not to be used with dates before 1970.

```SECONDS_IN_A_DAY = 60 * 60 * 24

-- Convert date string as YYYY-MM-DD to Epoch time.
function parseDate (str)
local y, m, d = string.match(str, "(%d+)-(%d+)-(%d+)")
return os.time({year = y, month = m, day = d})
end

-- Main procedure
io.write("Enter date 1: ")
io.write("Enter date 2: ")
local diff = math.ceil(os.difftime(d2, d1) / SECONDS_IN_A_DAY)
print("There are " .. diff .. " days between these dates.")
```
Output:
```Enter date 1: 1970-01-01
Enter date 2: 2019-10-02
There are 18171 days between these dates.```

## M2000 Interpreter

Version 12 has date type, so we can handle easy dates.

```module Days_between_dates{
date a="2019-01-01", b="2019-09-30"
long z=b-a
// Use the system default to display dates (DD/MM/YYYY)
Print "Days from "+a+" to "+b+" = "+z
// using locale 1033 to display dates (MM/DD/YYYY)
Print "Days from "+date\$(a, 1033)+" to "+date\$(b, 1033)+" = "+z
}
Days_between_dates```
Output:
```Days from 1/1/2019 to 30/9/2019 = 272
Days from 1/1/2019 to 9/30/2019 = 272
```

## Mathematica / Wolfram Language

```DateDifference["2020-01-01", "2020-03-01"]
DateDifference["2021-01-01", "2021-03-01"]
```
Output:
```Quantity[60, "Days"]
Quantity[59, "Days"]```

## Nim

```import times

proc daysBetween(date1, date2: string): int64 =
const Fmt = initTimeFormat("yyyy-MM-dd")
(date2.parse(Fmt, utc()) - date1.parse(Fmt, utc())).inDays

const Dates = [("1995-11-21","1995-11-21"),
("2019-01-01","2019-01-02"),
("2019-01-02","2019-01-01"),
("2019-01-01","2019-03-01"),
("2020-01-01","2020-03-01"),
("1902-01-01","1968-12-25"),
("2090-01-01","2098-12-25")]

for (date1, date2) in Dates:
echo "Days between ", date1, " and ", date2, ": ", daysBetween(date1, date2)
```
Output:
```Days between 1995-11-21 and 1995-11-21: 0
Days between 2019-01-01 and 2019-01-02: 1
Days between 2019-01-02 and 2019-01-01: -1
Days between 2019-01-01 and 2019-03-01: 59
Days between 2020-01-01 and 2020-03-01: 60
Days between 1902-01-01 and 1968-12-25: 24465
Days between 2090-01-01 and 2098-12-25: 3280```

## Perl

Would not reinvent this wheel.

```use feature 'say';
use Date::Calc qw(Delta_Days);

say Delta_Days(2018,7,13, 2019,9,13);   # triskaidekaphobia
say Delta_Days(1900,1,1,  2000,1,1);    # a century
say Delta_Days(2000,1,1,  2100,1,1);    # another, with one extra leap day
say Delta_Days(2020,1,1,  2019,10,1);   # backwards in time
say Delta_Days(2019,2,29, 2019,3,1);    # croaks
```
Output:
```427
36524
36525
-92
Date::Calc::PP::Delta_Days(): Date::Calc::Delta_Days(): not a valid date at Days_between_dates line 10```

## Phix

Library: Phix/basics
```include builtins\timedate.e
-- specify as many or as few permitted formats as you like:
set_timedate_formats({"YYYY-MM-DD","DD/MM/YYYY","YYYY/MM/DD"})

constant SECONDS_TO_DAYS = 60*60*24

procedure test(string d1, d2, desc="")
timedate td1 = parse_date_string(d1),
td2 = parse_date_string(d2)
atom s = timedate_diff(td1,td2,DT_DAY),
d = s/SECONDS_TO_DAYS
string e = elapsed(s)&desc
printf(1,"Days between %s and %s: %d [%s]\n",{d1,d2,d,e})
end procedure
test("1969-12-31","1970-01-01")
test("1995-11-21","1995-11-21",", same date")
test("2019-01-02","2019-01-01",", negative date")
test("2019-01-01","2019-03-01",", non-leap year")
test("2020-01-01","2020-03-01",", leap year")
test("1970-01-01", "2019/10/18")
test("1970-01-01", "18/10/2019")
```

As shown, timedate_diff() can optionally round to the nearest whole number of days [else omit DT_DAY].
Note that elapsed() assumes all years are exactly 365 days, and in no way takes leap years into consideration (as opposed, of course, to timedate_diff() which handles them flawlessly), not that you sh/c/would ever use the string output of elapsed() in any further calculations anyway.

Output:
```Days between 1969-12-31 and 1970-01-01: 1 [1 day]
Days between 1995-11-21 and 1995-11-21: 0 [0s, same date]
Days between 2019-01-02 and 2019-01-01: -1 [minus 1 day, negative date]
Days between 2019-01-01 and 2019-03-01: 59 [59 days, non-leap year]
Days between 2020-01-01 and 2020-03-01: 60 [60 days, leap year]
Days between 1970-01-01 and 2019/10/18: 18187 [49 years, 302 days]
Days between 1970-01-01 and 18/10/2019: 18187 [49 years, 302 days]
```

## PicoLisp

```(de diffDates (A B)
(abs (- (\$dat A "-") (\$dat B "-"))) )
(println (diffDates "2019-1-1" "2019-9-30"))
(println (diffDates "2015-12-31" "2016-09-30"))```
Output:
```272
274
```

## Python

```#!/usr/bin/python
import sys

''' Difference between two dates = g(y2,m2,d2) - g(y1,m1,d1)
Where g() gives us the Gregorian Calendar Day
Inspired  by discussion at:
https://stackoverflow.com/questions/12862226/the-implementation-of-calculating-the-number-of-days-between-2-dates
'''

def days( y,m,d ):
''' input year and month are shifted to begin the year in march'''
m = (m + 9) % 12
y = y - m/10

''' with (m*306 + 5)/10 the number of days from march 1 to the current 'm' month '''
result = 365*y + y/4 - y/100 + y/400 + (m*306 + 5)/10 + ( d - 1 )
return result

def diff(one,two):
[y1,m1,d1] = one.split('-')
[y2,m2,d2] = two.split('-')
# strings to integers
year2 = days( int(y2),int(m2),int(d2))
year1 = days( int(y1), int(m1), int(d1) )
return year2 - year1

if __name__ == "__main__":
one = sys.argv[1]
two = sys.argv[2]
print diff(one,two)
```
Output:
```python days-between.py 2019-01-01 2019-09-30
272
```

## QB64

```'Task
'Calculate the number of days between two dates.
'Date input should be of the form   YYYY-MM-DD.

from\$ = "2000-05-29"
to\$ = "2022-05-29"
Print NumberOfDays(from\$, to\$)

End

Function NumberOfDays (from\$, to\$)
NumberOfDays = 0
Dim As Integer Year(1 To 2), Mounth(1 To 2), Day(1 To 2)
Dim As Integer NumberD, Index
Year(1) = Val(Left\$(from\$, 4))
Year(2) = Val(Left\$(to\$, 4))
Mounth(1) = Val(Mid\$(from\$, 6, 2))
Mounth(2) = Val(Mid\$(to\$, 6, 2))
Day(1) = Val(Right\$(from\$, 2))
Day(2) = Val(Right\$(to\$, 2))

If Year(1) > Year(2) Then
Swap Year(1), Year(2)
Swap mount(1), mount(2)
Swap Day(1), Day(2)
End If

If Day(1) > Day(2) Then
Select Case Mounth(2) - 1
Case 4, 6, 9, 11
Day(2) = Day(2) + 30
Case 1, 3, 5, 7, 8, 10, 12
Day(2) = Day(2) + 31
Case 2
If (Index Mod 4 = 0) Or ((Index Mod 100 = 0) And (Index Mod 400 = 0)) Then Day(2) = Day(2) + 29 Else Day(2) = Day(2) + 28
End Select
Mounth(2) = Mounth(2) - 1
If Mounth(2) = 0 Then Year(2) = Year(2) - 1: Mounth(2) = 12
End If

NumberD = (Day(2) - Day(1)) + 1

For Index = Mounth(1) To Mounth(2) - 1 Step 1
Select Case Index
Case 4, 6, 9, 11
NumberD = NumberD + 30
Case 1, 3, 5, 7, 8, 10, 12
NumberD = NumberD + 31
Case 2
If (Index Mod 4 = 0) Or ((Index Mod 100 = 0) And (Index Mod 400 = 0)) Then NumberD = NumberD + 29 Else NumberD = NumberD + 28
End Select

Next

For Index = Year(1) To Year(2) - 1 Step 1
If (Index Mod 4 = 0) Or ((Index Mod 100 = 0) And (Index Mod 400 = 0)) Then NumberD = NumberD + 366 Else NumberD = NumberD + 365
Next Index
NumberOfDays = NumberD
End Function```

## Raku

(formerly Perl 6) Dates are first class objects in Raku and may have arithmetic in days done directly on them.

```say Date.new('2019-09-30') - Date.new('2019-01-01');

say Date.new('2019-03-01') - Date.new('2019-02-01');

say Date.new('2020-03-01') - Date.new('2020-02-01');

say Date.new('2029-03-29') - Date.new('2019-03-29');

say Date.new('2019-01-01') + 90;

say Date.new('2020-01-01') + 90;

say Date.new('2019-02-29') + 30;

CATCH { default { .message.say; exit; } };
```
```272
28
29
3653
2019-04-01
2020-03-31
Day out of range. Is: 29, should be in 1..28```

## REBOL

REBOL accepts a multitude of lexically recognized date! formats. date! is a builtin datatype. Slashes or dashes, year-month-day, day/month/year, or dd/monthname/year, etc. Math on dates defaults to days.

```prompt\$ rebol -q
>> 2019-11-24 - 2000-01-01
== 7267
>> 2019-nov-24 - 01-jan-2000
== 7267```

## REXX

Works with: Regina REXX

### bare bones version

Programming note:   the   B   (Base)   an option for the   date   BIF which indicates to compute the number of
days since the beginning of the Gregorian calendar,   and   I   which is the option that indicates the date is in
the   ISO   (International Standards Organization standard 8601:2004)   format.

```/*REXX program computes the number of days between two dates in the form of  YYYY-MM-DD */
parse arg \$1 \$2 .                                /*get 2 arguments (dates) from the C.L.*/
say abs( date('B',\$1,"I")  -  date('B',\$2,"I") )   ' days between '    \$1    " and "    \$2
/*stick a fork in it,  we're all done. */
```
output   when using the inputs of:     2019-10-02   2000-01-01
```7214  days between  2019-10-02  and  2000-01-01
```

### supports more variations

This REXX version supports more variations in the date format   (allows a single digit month and/or day), as well as
allowing a single asterisk   (*)   to be used for a date   (which signifies that the current date is to be used).

The dates may be specified in the following formats:

```       ,            (a comma)        indicates today's date
*            (an asterisk)    indicates today's date
yyyy-mm-dd   where yyyy may be a 2- or 4-digit year, mm may be a 1- or 2-digit month, dd may be a 1- or 2-digit day of month
mm/dd/yyyy   (as above)
mm/dd        (as above),  but the current year is assumed
dd\mm\yyyy   (as above)
dd\mm        (as above),  but the current year is assumed
```

Commas   (,)   are inserted into numbers where appropriate.

```/*REXX program computes the number of days between two dates in the form of  YYYY-MM-DD */
parse arg \$.1 \$.2 _ . 1 . . xtra                 /*obtain two arguments from the  C.L.  */
seps= '/-\';        yr.= .;   mon.= .;   dd.= .  /*define the defaults for both dates.  */
do a=1  for 2                        /*process both of the specified dates. */
if \$.a=='' | \$.a=="*" | \$.a==','  then \$.a= date("I")
do s=1  for length(seps)          /*process a specified date by separator*/
sep= substr(seps, s, 1)           /*obtain one of the supported sep char.*/
if pos(sep, \$.a)\==0  then call conv \$.a         /*parse the date string.*/
end   /*s*/
end      /*a*/
?.1= '1st'
?.2= '2nd'
if _ \== ''              then call err "too many arguments specified: "   xtra
dy.= 31                                          /*default number of days for all months*/
parse value 30 with dy.4 1 dy.6 1 dy.9 1 dy.11   /*define 30─day months, Feb. is special*/
@notCorr= "isn't in a support date format: "     /*used for a literal for an error msg. */

do j=1  for 2                                  /*examine both dates for correct format*/
if \$.j           ==''  then call err ?.j "date was not specified."
if length(yr.j)==0     then call err ?.j "year"  @notCorr '(missing)'
if isDec(yr.j)         then call err ?.j "year"  @notCorr '(has a non─decimal digit)'
if yr.j<1 | yr.j>9999  then call err ?.j "year"  @notCorr '(not in the range 1──►9999)'
if length(mon.j)==0    then call err ?.j "month" @notCorr '(missing)'
if isDec(mon.j)        then call err ?.j "month" @notCorr '(has a non─decimal digit)'
if mon.j<1 | mon.j>12  then call err ?.j "month" @notCorr '(not in the range 1──►12)'
if length(dd.j)==0     then call err ?.j "day"   @notCorr '(missing)'
if isDec(dd.j)         then call err ?.j "day"   @notCorr '(has a non─decimal digit)'
mo= mon.j
if leapYr(yr.j)  then dy.2= 29                 /*Is it a leapyear? Use 29 days for Feb*/
else dy.2= 28                 /*Isn't "     "      "  28   "   "   " */
if dd.j<1 | dd.j>dy.mo then call err ?.j "day"   @notCorr '(day in month is invalid)'

yr.j= right( yr.j  +0, 4, 0)                 /*force YYYY to be four decimal digits.*/
mon.j= right(mon.j  +0, 2, 0)                 /*  "    MON  "  "  two    "       "   */
dd.j= right( dd.j  +0, 2, 0)                 /*  "     DD  "  "   "     "       "   */
\$.j= yr.j'-'mon.j"-"dd.j                    /*reconstitute a date from above parts.*/
end       /*j*/

between= abs( date('B', \$.1, "I")  -  date('B', \$.2, "I") )     /* # days between dates.*/
parse source . how .                                            /*determine how invoked.*/
if how='COMMAND'  then say commas(between)    ' days between '     \$.1     " and "     \$.2
exit between                                     /*stick a fork in it,  we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
commas: parse arg _; do c_=length(_)-3  to 1  by -3; _=insert(',', _, c_);  end;  return _
err:    say; say '***error*** ' arg(1);  exit 13 /*issue an error message (with text)   */
isDec:  return verify( arg(1), 1234567890) \== 0 /*insure argument is just decimal digs.*/
leapYr: arg _; ly=_//4==0; if ly==0  then return 0; ly=((_//100\==0)|_//400==0); return ly
serDAT: call err 'illegal date format with a separator= ['sep"],   date= "       @dat
/*──────────────────────────────────────────────────────────────────────────────────────*/
conv:   parse arg @dat                           /*obtain date that the user specified. */
if sep=='-'  then parse var  @dat    yr.a  "-"  mon.a  '-'  dd.a    /* yy-mm-dd */
if sep=='/'  then parse var  @dat   mon.a  "/"   dd.a  '/'  yr.a    /* mm/dd/yy */
if sep=='\'  then parse var  @dat    dd.a  "\"  mon.a  '\'  yr.a    /* dd\mm\yy */
if yr.a==''  then yr.a= right( date(), 4)                           /*omitted yy*/
if length(yr.a)==2  then yr.a= left( date('S'), 2)yr.a              /*2 dig yy ?*/
if yr.a==.  |  mon.a==.  |  dd.a==.  then call serDAT               /*validate. */
return
```
output   when using the inputs of:     *   2000-1-1

Today   (indicated by the asterisk)   is   2019-10-2

```7,214  days between  2019-10-02  and  2000-01-01
```

## Ring

```load "stdlib.ring"

DaysBetween = [["1995-11-21","1995-11-21"],
["2019-01-01","2019-01-02"],
["2019-01-02","2019-01-01"],
["2019-01-01","2019-03-01"],
["2020-01-01","2020-03-01"],
["1902-01-01","1968-12-25"],
["2090-01-01","2098-12-25"]]

for n = 1 to len(DaysBetween)
date1 = DaysBetween[n][1]
date2 = DaysBetween[n][2]
date3 = substr(date1,9,2) + "/" + substr(date1,6,2) + "/" + substr(date1,1,4)
date4 = substr(date2,9,2) + "/" + substr(date2,6,2) + "/" + substr(date2,1,4)
? "Days between " + DaysBetween[n][1] + " and " + DaysBetween[n][2] + ": " + diffdays(date4,date3)
next```
Output:
```Days between 1995-11-21 and 1995-11-21: 0
Days between 2019-01-01 and 2019-01-02: 1
Days between 2019-01-02 and 2019-01-01: -1
Days between 2019-01-01 and 2019-03-01: 59
Days between 2020-01-01 and 2020-03-01: 60
Days between 1902-01-01 and 1968-12-25: 0
Days between 2090-01-01 and 2098-12-25: 3280
```

## RPL

Uses Python formula, in a forced binary calculation mode to avoid 'flooring' instructions

Works with: Halcyon Calc version 4.2.7
```≪ → d m y
≪ m 9 + 12 MOD
y OVER #10d / -
DUP 365 * OVER #4d / + OVER #100d / - SWAP #400d / +
SWAP 306 * 5 + #10d / + d + 1 - B→R
≫ ≫
'GREGN' STO

≪ SWAP 1 2 START
→ date
≪ date 9 10 SUB STR→ date 6 7 SUB STR→ date 1 4 SUB STR→
GREGN SWAP
≫
NEXT -
≫
'NBDAYS' STO
```
```"1902-01-01" "1968-12-25" NBDAYS
"2019-01-02" "2019-01-01" NBDAYS
"2019-01-01" "2019-03-01" NBDAYS
"2020-01-01" "2020-03-01" NBDAYS
```
Output:
```4: 24465
3: -1
2: 59
1: 60
```

## Ruby

```require "date"

d1, d2 = Date.parse("2019-1-1"), Date.parse("2019-10-19")

p (d1 - d2).to_i  # => -291
p (d2 - d1).to_i  # => 291
```

## Rust

```// [dependencies]
// chrono = "0.4"

use chrono::NaiveDate;

fn main() {
let args: Vec<String> = std::env::args().collect();
if args.len() != 3 {
eprintln!("usage: {} start-date end-date", args[0]);
std::process::exit(1);
}
if let Ok(start_date) = NaiveDate::parse_from_str(&args[1], "%F") {
if let Ok(end_date) = NaiveDate::parse_from_str(&args[2], "%F") {
let d = end_date.signed_duration_since(start_date);
println!("{}", d.num_days());
} else {
eprintln!("Can't parse end date");
std::process::exit(1);
}
} else {
eprintln!("Can't parse start date");
std::process::exit(1);
}
}
```
Output:
```days_between_dates 2020-01-01 2020-09-06
249
```

## Scala

```object DaysBetweenDates {

/*Inspired by the Python version of the algorithm and the discussion here
https://stackoverflow.com/questions/12862226/the-implementation-of-calculating-the-number-of-days-between-2-dates.*/

/**Transform a date into a day number in the Gregorian Calendar*/
def dateToDays(year : Int, month : Int, day : Int ) : Int = {
val m = (month+ 9) % 12
val y = year - m/10
val d = day
365*y + y/4 - y/100 + y/400 + (m*306 + 5)/10 + (d - 1)
}

/**Compute the difference of days between both input dates*/
def daysDifference(firstDate : String, secondDate : String) : Int = {
val firstDateTuple = firstDate.split('-') match { case Array(a, b, c) => (a, b, c) }
val secondDateTuple = secondDate.split('-') match { case Array(a, b, c) => (a, b, c) }

val firstYear = dateToDays( firstDateTuple._1.toInt, firstDateTuple._2.toInt, firstDateTuple._3.toInt)
val secondYear = dateToDays( secondDateTuple._1.toInt, secondDateTuple._2.toInt, secondDateTuple._3.toInt )

return secondYear - firstYear
}

def main(args: Array[String]): Unit = {
println(daysDifference("2019-01-01", "2019-09-30"))
println(daysDifference("1995-11-21", "1995-11-21"))
println(daysDifference("2019-01-01", "2019-01-02"))
println(daysDifference("2019-01-02", "2019-01-01"))
println(daysDifference("2019-01-01", "2019-03-01"))
println(daysDifference("2020-01-01", "2020-03-01"))
println(daysDifference("1902-01-01", "1968-12-25"))
println(daysDifference("2090-01-01", "2098-12-25"))
println(daysDifference("1902-01-01", "2098-12-25"))
}

}
```
Output:
```272
0
1
-1
59
60
24465
3280
71947
```

## SenseTalk

SenseTalk supports date and time calculations in many forms, and many different units of time (such as 'days' in this example). Rounding is needed due to daylight savings time changes.

```set startDate to "2020-03-13"
set endDate to "2021-07-14"

put (endDate - startDate) rounded to nearest day```
Output:
```488 days
```

## Sidef

```require('Date::Calc')

func days_diff(a,b) {
%S<Date::Calc>.Delta_Days(a.split('-')..., b.split('-')...)
}

var date1 = "1970-01-01"
var date2 = "2019-10-02"

say "Date 1: #{date1}"
say "Date 2: #{date2}"

var days = days_diff(date1, date2)

say "There are #{days} days between these dates"
```
Output:
```Date 1: 1970-01-01
Date 2: 2019-10-02
There are 18171 days between these dates
```

## Swift

```import Foundation

func daysFromTimeInterval(_ interval: Double) -> Int {
return Int(interval) / 86400
}

let formatter = DateFormatter()

formatter.dateFormat = "yyyy-MM-dd"

print("Enter date one (yyyy-MM-dd): ", terminator: "")

guard let date1Str = readLine(strippingNewline: true), let date1 = formatter.date(from: date1Str) else {
fatalError("Invalid date two")
}

print("Enter date two (yyyy-MM-dd): ", terminator: "")

guard let date2Str = readLine(strippingNewline: true), let date2 = formatter.date(from: date2Str) else {
fatalError("Invalid date two")
}

let (start, end) = date1 > date2 ? (date2, date1) : (date1, date2)
let days = daysFromTimeInterval(DateInterval(start: start, end: end).duration)

print("There are \(days) days between \(start) and \(end)")
```
Output:
```Enter date one (yyyy-MM-dd): 2019-01-01
Enter date two (yyyy-MM-dd): 2019-12-02
There are 335 days between 2019-01-01 05:00:00 +0000 and 2019-12-02 05:00:00 +0000```

## UNIX Shell

Works with: Bourne Again Shell
```# return true if year is leap in Gregorian calendar
leap() {
local -i year
year=\$1
if (( year % 4 )); then return 1; fi
if (( year % 100 )); then return 0; fi
! (( year % 400 ))
}

# convert date to Gregorian day count (Rata Die), where RD 1 = January 1, 1 CE
rd() {
local year month day
IFS=- read year month day <<<"\$1"
local -i elapsed_years=year-1
(( day += elapsed_years * 365 ))
(( day += elapsed_years/4 ))
(( day -= elapsed_years/100 ))
(( day += elapsed_years/400 ))
local month_lengths=(31 28 31 30 31 30 31 31 30 31 30 31)
if leap "\$year"; then let month_lengths[1]+=1; fi
local m
for (( m=0; m<month-1; ++m)); do
(( day += month_lengths[m] ))
done
printf '%d\n' "\$day"
}

days_between() {
local -i date1 date2
date1=\$(rd "\$1")
date2=\$(rd "\$2")
printf '%d\n' \$(( date2 - date1 ))
}

days_between 1970-01-01 2019-12-04
```
Output:
`18234`

## Visual Basic .NET

Translation of: C#
```Imports System.Globalization

Module Module1

Function DateDiff(d1 As String, d2 As String) As Integer
Dim a = DateTime.ParseExact(d1, "yyyy-MM-dd", CultureInfo.InvariantCulture)
Dim b = DateTime.ParseExact(d2, "yyyy-MM-dd", CultureInfo.InvariantCulture)
Return (b - a).TotalDays
End Function

Sub Main()
Console.WriteLine(DateDiff("1970-01-01", "2019-10-18"))
End Sub

End Module
```
Output:
`18187`

## V (Vlang)

Translation of: go
```import time

fn days_between(d1 string, d2 string) ?int {
t1 := time.parse('\$d1 01:01:01')?
t2 := time.parse('\$d2 01:01:01')?
days := int((t2-t1).hours()/24)
return days
}
fn main(){
mut date1,mut date2 := "2019-01-01", "2019-09-30"
mut days := days_between(date1, date2)?
println("There are \$days days between \$date1 and \$date2")

date1, date2 = "2015-12-31", "2016-09-30"
days = days_between(date1, date2)?
println("There are \$days days between \$date1 and \$date2")
}```
Output:
```There are 272 days between 2019-01-01 and 2019-09-30
There are 274 days between 2015-12-31 and 2016-09-30```

## Wren

Library: Wren-date
```import "/date" for Date

var datePairs = [
["1995-11-21", "1995-11-21"],
["2019-01-01", "2019-01-02"],
["2019-01-02", "2019-01-01"],
["2019-01-01", "2019-03-01"],
["2020-01-01", "2020-03-01"],
["1902-01-01", "1968-12-25"],
["2090-01-01", "2098-12-25"],
["1902-01-01", "2098-12-25"],
["1970-01-01", "2019-10-18"],
["2019-03-29", "2029-03-29"],
["2020-02-29", "2020-03-01"]
]
for (dates in datePairs) {
var date1 = Date.parse(dates[0])
var date2 = Date.parse(dates[1])
var days = (date2 - date1).days
Date.default = Date.isoDate
System.print("Days between %(date1) and %(date2) = %(days)")
}
```
Output:
```Days between 1995-11-21 and 1995-11-21 = 0
Days between 2019-01-01 and 2019-01-02 = 1
Days between 2019-01-02 and 2019-01-01 = -1
Days between 2019-01-01 and 2019-03-01 = 59
Days between 2020-01-01 and 2020-03-01 = 60
Days between 1902-01-01 and 1968-12-25 = 24465
Days between 2090-01-01 and 2098-12-25 = 3280
Days between 1902-01-01 and 2098-12-25 = 71947
Days between 1970-01-01 and 2019-10-18 = 18187
Days between 2019-03-29 and 2029-03-29 = 3653
Days between 2020-02-29 and 2020-03-01 = 1
```

## zkl

```var [const] TD=Time.Date;
today:=TD.parseDate("--");  // "yyyy-mm-dd" and variations --> (y,m,d)
// or Time.Clock.UTC  --> (y,m,d,h,m,s)
then:=TD.parseDate("2018-9-30");
diff:=TD.deltaDays(then,today.xplode());  // ( (y,m,d), y,m,d )
println("Number of days between %s and %s: %d".fmt(then,today,diff));
println("Number of days between %s and %s: %d".fmt(
TD.toYMDString(today.xplode()),	// to(y,m,d) not to((y,m,d))
TD.toYMDString(then.xplode()),
```Number of days between L(2018,9,30) and L(2019,9,30): 365