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Date calculator
Days between two dates, what date falls a given distance away, or how long until something — with working days counted properly, which is the number most calculators leave out and most deadlines actually run on.
Working days, and why the count is the argument
Almost every dispute about a date is really a dispute about counting. "Ten working days" from a Monday is a Friday if you count the start day and the following Monday if you do not, and both parties are certain they are right.
This tool counts inclusively — both end dates are in the range — so Monday to Friday is five working days, not four. That matches how people speak and how most notice periods and delivery estimates are written. The headline number above is the elapsed count, which is the other convention, so you can see both and know which one a document means.
The weekend is selectable because a great deal of the world does not take Saturday and Sunday. Saudi Arabia, Qatar and Oman run Sunday to Thursday; the UAE moved to a Monday–Friday week in 2022. Getting that wrong turns a five-day estimate into a seven-day one.
Public holidays are deliberately not included. They differ by country, by province, by year, and several move with the moon. A calculator that quietly assumed a holiday calendar would be wrong for most of the people using it and would give no sign of it.
31 January plus one month
There is no 31 February, so something has to give, and the two available answers are genuinely different dates. Clamping gives 28 February — the last day of the target month. Rollinggives 3 March, because the overflow spills into the next month.
JavaScript's own date handling rolls. That is why so many calculators get month ends subtly wrong without anyone noticing until an invoice is dated three days late. This one clamps, which is what a person means by "a month later" and what most contracts assume.
The same choice shows up in the other direction. Between 31 January and 1 March, a naive breakdown produces "one month and minus two days" — genuinely, that is what the standard borrow arithmetic returns, because one borrow of February's 28 days does not cover a 30-day shortfall. This page counts whole months forward while they still fit and measures the remainder, which cannot produce a negative and gives one month and one day.
Why the arithmetic runs in UTC
Not for tidiness. In any country that changes its clocks, one day of the year is 23 hours long and one is 25. A calculator that subtracts two local timestamps and divides by 86,400,000 therefore returns a fractional number of days twice a year, and rounding it gives an answer one day out.
UTC has no such day. Every date here is turned into a UTC midnight before anything is compared, which makes the day count exact everywhere in the world and on every date, including the changeover days themselves. The time zone converter is the tool for when the clock time itself matters.
This one, or the age calculator?
They answer the same arithmetic for different purposes. Use the age calculator for people: it gives exact age, the Hijri date, and handles the leap-day birthday question. Use this one for paperwork: working days, a settable weekend, adding a notice period, counting down to a deadline.
Questions
Does it include the end date?
The working-days row does, so Monday to Friday is five. The big number does not — it is the elapsed count. Both are shown because documents use both and rarely say which.
Are public holidays counted?
No, deliberately. They vary by country, province and year, and several move with the lunar calendar. Subtract your own.
What does it do with 31 January plus a month?
Gives 28 February — it clamps to the end of the target month rather than rolling into March.
Is anything sent anywhere?
No. It runs entirely in your browser.
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