Date Calculator
Days between two dates, adding and subtracting days, weeks, months and years, and an exact age — all worked out in your browser.
Runs in your browserDifference between dates
Pick two dates to see the difference between them.
About this tool
Three questions that look trivial and are not. How many days lie between two dates; what date you land on after adding three months and ten days; how old someone is exactly, down to the day. Calendars make all three awkward, because months are 28 to 31 days long and years are 365 or 366, so the answers cannot come from dividing by a fixed number. This tool does the arithmetic the way a calendar does. It also counts weekdays, and it is careful about the two places where this kind of calculator usually goes wrong: adding a month to the 31st, and daylight saving. Everything runs locally, and there is nothing to sign up for.
How to use it
- 1For a difference, pick the two dates. The result shows calendar days, the same span broken into years, months and days, weeks with a remainder, and how many of those days are weekdays.
- 2For arithmetic, give a starting date, an amount and a unit, then choose whether to go forward or back. Month and year shifts keep the day of the month where the calendar allows it.
- 3For an age, enter a birth date. Leave the reference date empty to use today, or set it to work out an age as it stood on some past date.
Frequently asked questions
I added one month to 31 January and got 28 February. Is that a bug?
No, that is deliberate, and the alternative is worse. A month has no fixed length, so "one month after 31 January" has no exact answer. What many date libraries do is push the overflow forward and return 3 March, which silently adds days that were never asked for. This tool instead clamps to the last valid day of the target month: 31 January plus one month is the last day of February. The same applies to 29 February plus one year, which lands on 28 February. The rule is stated in the panel so the result never looks arbitrary.
Why does the weekday count not match the number of days that are not weekends?
Because the two are counted over slightly different spans on purpose. The calendar-day figure includes both dates unless you turn that off; the weekday figure does not count the start day but does count the end day, which is the convention people expect when they ask how many working days lie ahead. The panel labels both figures, and with both-start-and-end turned on the two add up to the total. Public holidays are not deducted at all — see below.
Does the weekday count subtract public holidays?
No, and it should not pretend to. Public holidays are set per country, change every year, and include regional and one-off dates; there is no single source that would be right for everyone. A hard-coded holiday list would be wrong more often than it was right, and quietly wrong, which is the worst kind. Treat the weekday count as "Monday to Friday" and subtract your own holidays, or check an official calendar for the country concerned.