Days between dates / add to a date

How to use it

1. Days between dates: type the start and end dates (the end is today until you change it), with A.D. or B.E. years. The answer shows at once.
2. Tick "Count the first day too" when both ends count, such as days of leave, nights booked or days of a contract.
3. To add or subtract: open the second tab, type a start date, how many and the unit, such as 90 days from today or 6 months back.

How it is worked out

Days = end date − start date on the calendar (1 January to 31 December 2026 is 364 days, or 365 counting the first day). Leap years have a 29 February and 366 days. Work days are the Mondays to Fridays among the days counted. "Months" counts whole calendar months, then the days left.

Adding months or years keeps the day of the month; when the month it lands in is shorter, its last day is used (31 January + 1 month = 28 February, or 29 in a leap year). The page works with calendar days only, so daylight saving time and the time zone of your device never shift the answer. For an age from a date of birth, use the age calculator; to turn dates between A.D. and B.E., use the Thai date converter.

Good to know

• Work days do not take off public holidays, which change from year to year and between employers. Subtract the ones that fall in your range.
• Laws and contracts sometimes count days their own way (leaving out the first day, or moving to the next business day). Check those rules.
• Everything is worked out on your device. No date is sent anywhere.

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