Date Calculator
Count the days between two dates — including working days only — or project forwards and backwards from a starting date.
How to use the Date Calculator
- Choose whether you are measuring between two dates or projecting from one.
- Fill in the dates, or the amount and unit to add or subtract.
- Press Calculate. Business-day counts skip Saturdays and Sundays.
Inclusive versus exclusive counting
"How many days from Monday to Friday?" has two correct answers. Four, if you count the gaps between days. Five, if you count the days themselves. Neither is wrong — they answer different questions.
The distinction matters in contracts and deadlines. A "30 day notice period" starting on the 1st usually ends on the 31st (exclusive counting), but a "5 working days to respond" usually includes the day you received it. The checkbox here lets you pick, and legal or contractual terms should define which they mean.
Months are not a fixed length
Adding one month to 31 January is ambiguous — there is no 31 February. JavaScript's date arithmetic, which this tool uses, rolls forward to 2 or 3 March. Some systems clamp to the last day of the month instead, giving 28 or 29 February.
Neither convention is universal, which is why financial and legal documents specify the rule explicitly. If exact month-end behaviour matters, work in days rather than months, or check the result before relying on it.
Business days exclude weekends, not holidays
The business-day count here skips Saturdays and Sundays only. Public holidays vary by country, region and year — and in some places by industry — so no general-purpose calculator can include them without knowing exactly where you are.
Some countries also have a different working week: Friday and Saturday are the weekend across much of the Middle East. For a legally binding deadline, count against the official calendar that applies.
Frequently asked questions
Does it account for leap years?
Yes. Day counts use real calendar arithmetic, so 29 February is included whenever it falls within the range.
Why is the month figure marked approximate?
Months vary between 28 and 31 days, so any conversion from days to months uses an average — 30.44 days. For exact month arithmetic, use the add or subtract mode.
Can I exclude public holidays?
Not automatically, since holidays differ by country and change each year. Count the business days here, then subtract the holidays that fall in the range.
Does it handle dates before 1970 or far in the future?
Yes, across a range of roughly ±270,000 years. Very distant dates use the proleptic Gregorian calendar, which differs from the Julian calendar historically in use before 1582.
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