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Date Difference Calculator
Days between dates, add or subtract days, and business-day counts.
What it does. A date calculator finds the interval between two dates, or shifts a date forward or backward by a given period. This tool reports the gap in days, weeks, months and years, counts business days excluding weekends, and adds or subtracts any combination of days, weeks, months and years.
Runs in your browserNothing uploadsNo signupWorks offline
How to use Date Difference Calculator
- Choose a mode: difference between two dates, or add and subtract from one date.
- Enter the dates, or the amount to shift by.
- Read the result in days, weeks, months and years, plus the business-day count.
Why do date calculations disagree about months?
Because a month is not a fixed length, and "one month after 31 January" has no unambiguous answer.
Two conventions exist. Clamping gives 28 February (or 29 in a leap year) — the last valid day of the target month. Overflow gives 2 or 3 March by counting past the end.
This tool clamps, which is what almost every legal and financial system does. A contract dated 31 January with a one-month term expires on 28 February, and a monthly subscription started on the 31st bills on the 28th in February and returns to the 31st in March.
The consequence is that adding one month twice is not the same as adding two months. 31 January plus one month is 28 February; plus another month is 28 March. Adding two months directly gives 31 March. Both are defensible; consistency within a system matters more than which is chosen.
How are business days counted?
Business days exclude Saturdays and Sundays. Whether they exclude public holidays depends on the jurisdiction, and there is no international standard.
This calculator excludes weekends by default and offers holiday sets for the US federal calendar, England and Wales bank holidays, Canadian statutory holidays, and the main EU member states. Regional variation is real — Scotland and Northern Ireland differ from England and Wales, and US state holidays differ from federal ones.
The distinction matters commercially. "Net 30" payment terms usually mean 30 calendar days; "within 5 business days" for a refund means something quite different across a holiday period. A shipment quoted at 3 business days ordered on the Friday before a US Monday holiday arrives on Thursday, not Monday.
What can I use this for?
- Contract and notice periods. A 90-day notice period served today ends on a specific date, and getting it wrong has legal consequences.
- Project planning. Business-day counts between milestones are what actually determine a schedule, since nothing happens at the weekend.
- Payment terms. Net 30, net 60 and net 90 due dates, and how many working days remain before one.
- Statutory deadlines. Filing windows, appeal periods, cooling-off periods and limitation periods are all defined in days from a trigger date.
- Travel and visa rules. The Schengen 90-in-180-day rule requires counting days across a rolling window, which is exactly the kind of arithmetic people get wrong.
- Countdowns. Days until a launch, a deadline, an event or a renewal.
How does the calculation handle leap years and DST?
Leap years are handled exactly. Every year divisible by 4 has 29 days in February, except centuries not divisible by 400 — so 1900 had 28 and 2000 had 29. Any span crossing a 29 February includes it.
Daylight saving is deliberately excluded, because this is date arithmetic rather than time arithmetic. The days when clocks change are 23 or 25 hours long, but they are still one day. Counting in hours across a DST boundary and dividing by 24 introduces an off-by-one error, which is why the calculation operates on calendar dates directly.
Note that the US and EU change clocks on different dates — the US in early November and mid-March, the EU on the last Sundays of October and March — so there are two weeks each year when the usual offset between them is an hour out. That affects meeting times, not day counts.
Frequently asked questions
How many days are between two dates?
Enter both and the tool reports the exact count. Whether the end date is included is a choice — the tool shows both the inclusive and exclusive figures.
Does it count weekends?
The total-days figure includes them. The business-days figure excludes weekends, and optionally public holidays for your country.
How do I add 90 days to a date?
Use add mode, enter 90 days, and the result accounts for month lengths and any leap day in the span.
What is the difference between 3 months and 90 days?
Usually two or three days. Three months from 1 January is 1 April, which is 90 days. Three months from 1 March is 1 June, which is 92 days.
Which holidays does it exclude?
US federal, England and Wales bank holidays, Canadian statutory holidays, and the main EU national holidays. Regional variations within a country are not covered.
Can I calculate a date in the past?
Yes. Subtract mode shifts backward, and the difference mode handles dates in either order.
Are my dates uploaded?
No. All arithmetic runs in this page.