Date calculator

Neither endpoint is double-counted: the result is the gap between the two dates. From the 1st to the 8th of a month is seven days, not eight. If you are counting occupied days rather than the interval between them, for example nights in a hotel against days of a rental, add one to the total yourself.

Because a calendar month is not a fixed number of days. Three months can be 89, 90, 91 or 92 days depending on which months they are, so a gap expressed as "two years, three months and 17 days" cannot be turned back into a day count by multiplication. The calculator shows both figures precisely because they answer different questions.

Yes. Switch the calculation to "Add or subtract from a date", then set the direction to Subtract. The same clamping rule applies in reverse: one month before March 31 is February 28 or February 29, because the 31st does not exist in February.

No. This is date arithmetic, not clock arithmetic. The calculator works on calendar dates, so the hour of day, your time zone and the one-hour clock shifts in spring and autumn have no effect. If you need the hours and minutes between two clock readings, use the time duration calculator instead.

It uses the proleptic Gregorian calendar, which extends today’s calendar rules backwards indefinitely. That matches how databases and spreadsheets count, but for dates before the Gregorian reform, which most of Europe adopted in 1582 and Britain and its colonies not until 1752, a historical record may be written in the Julian calendar and sit up to 11 days away from what you see here.