Date Calculator

The page holds three independent calculators. Days Between Two Dates measures the span from one date to another. Add or Subtract from a Date moves a starting date forwards or backwards by a number of days, weeks, months or years. Date Information takes a single date and tells you everything the calendar knows about it. Nothing is shared between the three panels, so you can use one and ignore the rest.

Days Between counts the nights, not the calendar squares. From 1 January to 31 January is 30 days, because the start date is not counted and the end date is. This is the same convention as a hotel stay, a bank interest period, or JavaScript's own date arithmetic, and it is what you want for deadlines: a contract signed on the 1st with a 30-day term expires on the 31st. If you need the inclusive count (how many calendar days the range touches, which is what you want when counting holiday entitlement or days of attendance), add one to the total.

Working days counts every day in the range that is not a Saturday or a Sunday. It does not know about public holidays, because those differ by country, region and sometimes by employer, and a wrong holiday list is worse than none. If your jurisdiction has, say, eight public holidays in the period, subtract eight from the figure shown. The same caveat applies to the Skip weekends option in the Add panel: it steps over Saturdays and Sundays only.

The Weeks, Months and Years figures are calendar-based, not divisions of the day count. Months are counted as whole calendar months elapsed, so 31 January to 1 March is 1 month, not 1.03 months. The tool checks whether the day-of-month has been reached, exactly the way an anniversary or a billing cycle works. Weeks are the whole number of seven-day periods in the total; if weeks are the unit you actually want, the Weeks Between Dates Calculator on this site answers that question directly.

Adding months and years clamps to the end of the target month. 31 January plus one month is 28 February (29 February in a leap year), because 31 February does not exist. Adding a further month from there gives 28 March, not 31 March, because the clamp is not remembered. Every date library and every accounting system has to make this choice, and clamping is the one nearly all of them make.

Date Information returns the day of the week, the full written date, the ISO 8601 week number, the day of the year out of 365 or 366, whether the year is a leap year, and the Unix timestamp for midnight UTC on that date. The day-of-year figure is useful for anything that runs on Julian day numbering: crop planning, some scientific data sets, and a lot of legacy mainframe date formats.

All arithmetic runs in UTC. This matters more than it sounds: doing date maths in local time is the classic source of off-by-one-day bugs, because a day is 23 or 25 hours long when the clocks change. By pinning every date to midnight UTC the tool gives the same answer in March as in July, and the same answer in Auckland as in Los Angeles.

For a countdown to a holiday rather than a span between two dates you type, the Days Until Calculator on this site has presets for Christmas, Easter, Thanksgiving and Halloween.

Everything is computed by JavaScript in your browser. There is no backend and no request is made when you change a date. Open DevTools, go to the Network tab, and use the tool to confirm.