Date Calculator
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A date interval is just one subtraction, done properly: turn each date into a count of days from a fixed starting point, then subtract. That is what this tool does, so leap years, long and short months, and year boundaries never get smoothed away by an estimate. January 1, 2026 to April 3, 2026 is 92 days — 30 remaining days in January, 28 in February, 31 in March, plus 3 days in April. Guessing 30 days per month would give 90, a full two days short, which is why dates must never be multiplied by an average month. The calendar breakdown works the same way: whole years are taken off first, then whole months, and what is left is the day count. February 29, 2024 to March 1, 2025 breaks down as 1 year, 0 months, 1 day — not 365 divided by 30.
Three kinds of question cover most uses. The first is leave and project time: how many working days sit inside a holiday, how many days and weeks run from kickoff to delivery, and whether a notice period, payment term, or probation period ends on the right day — missing by one day can mean missing a deadline. The second is travel and events: how many days until departure, how many nights a hotel stay covers, how many weeks of preparation remain. These are the same calculation, but whether the last day counts changes the answer, so the two counting rules are kept separate. The third is pushing a date forward or back: a signing date plus 90 days, a billing date plus 30 days, a birthday some number of days away — all answered on the same page without counting squares on a calendar.
Four edge cases cause most mistakes. The first is the end date: by default it is not counted, so January 1 to January 5 is 4 days; ticking the box counts both ends and gives 5 days. Leave counted in days usually wants the box ticked; a hotel stay counted in nights wants the default, since January 1 to January 5 is 4 nights. The second is holidays: weekdays here mean Monday to Friday only, with no public holidays removed, so statutory holidays, rescheduled days off, and company closures must be subtracted by hand — especially when the count feeds a contract or a leave form. The third is month-end clamping: January 31 plus 1 month has no February 31 to land on, so it falls back to February 28, or February 29 in a leap year, and February 29 plus 1 year falls back to February 28 the next year. The fourth is reversed dates: when the end date comes before the start date, the interval is the absolute value and does not change, while the weekday lines still show each date you entered.
Two examples you can check by hand. Example one: Monday, March 2, 2026 to Monday, June 15, 2026 is 105 days, exactly 15 weeks, breaking down as 3 months and 13 days, with 75 weekdays and 30 weekend days — because both ends are Mondays, there is no leftover week, and weekdays are exactly five sevenths of the total. Example two: January 31, 2026 plus 1 month gives February 28, 2026, while the same base date minus 30 days gives January 1, 2026. Type either example into the tool and compare; if a number disagrees, the counting rule for the end date or the month-end rule is the first place to look.
How to use
- Count an interval: pick the days-between mode, enter a start and an end date, and leave the end date uncounted by default; tick the box when leave counted in days needs both ends included.
- Read the breakdown: total days, whole weeks with remaining days, weekdays and weekend days, and a calendar breakdown in years, months, and days appear together, plus the weekday of each date you entered.
- Push a date forward or back: switch to the add/subtract mode, enter a base date, choose add or subtract, then fill in years, months, and days — applied in that order, years first, months second, days last.
- Check month-end results: when the result would land on a day the month does not have, such as January 31 plus 1 month, it falls back to that month's last day. That is real calendar arithmetic, not an error.
- Copy the result: copy the total days with weekdays and weekend days, or the resulting date, straight into a leave form, a contract, or a calendar entry.
FAQ
Does the count between two dates include the last day?
By default, no: January 1 to January 5 is 4 days, which is the plain subtraction of the two dates. Ticking the include box counts both ends and gives 5 days. Leave counted in days usually wants the box ticked; a hotel stay counted in nights wants the default. Picking the wrong rule is how most one-day errors happen.
Are public holidays removed from the weekday count?
No. Weekdays here mean Monday to Friday only, with no public holidays removed. Statutory holidays, rescheduled days off, and company closures must be subtracted by hand. If a stretch shows 10 weekdays and 2 of them are public holidays, the real working count is 8 — a step that matters whenever the number feeds a contract or a leave form.
Why does January 31 plus 1 month give February 28?
Because February has no 31st. Adding or subtracting applies years first, then months, then days, and when the result would land on a day the month does not have, it falls back to that month's last day: January 31 plus 1 month is February 28, or February 29 in a leap year, and February 29 plus 1 year is February 28 the next year. That is the real calendar rule, not rounding.
What happens when the end date is before the start date?
The interval is the absolute value and does not change: June 15, 2026 to March 2, 2026 is 105 days, the same as the other way round. The weekday lines still show each date you entered, so you can see which one comes first and which one comes second.
How are leap years handled?
By the Gregorian rule: a year divisible by 4 but not by 100 is a leap year, unless it is also divisible by 400. So 2028 is a leap year, while 2026 and 2100 are not. An interval crossing February 29 includes that day: February 1 to March 1 is 29 days in 2028 and 28 days in 2026.