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CalculatorDate Calculator
Two jobs in one tool: work out how many days sit between two dates, or move a date forward or backward by days, weeks or months. Switch on the working-days toggle when weekends should not count.
Result
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The fence-post mistake behind most deadline disputes
Ask "how many days between 1 March and 8 March" and two honest answers exist: 7 if you count the gap, 8 if you count every date including both ends. This is the classic fence-post problem — if you build a fence with posts every metre for 7 metres, you need 8 posts, not 7. Software defaults to the gap (exclusive) unless told otherwise, which is why this calculator's default matches "days between" but offers an inclusive toggle.
Contracts and deadlines usually mean the exclusive count — "payment due 30 days from invoice date" means 30 days after, not the invoice date itself as day one. But anything phrased as "for 5 days" covering a stay, a rental or a booking usually means inclusive: check-in day and check-out day both count as days you had the room. Read the wording before trusting either default.
Calendar days versus working days
Because a full seven-day week always contains exactly five weekdays and two weekend days — regardless of which day it starts on — any span that is an exact multiple of a week converts to working days with a clean rule: multiply the week count by 5. Spans that are not exact multiples need the starting weekday too, which is why the tool counts day by day rather than guessing.
| Weeks | Calendar days | Working days |
|---|---|---|
| 1 | 7 | 5 |
| 2 | 14 | 10 |
| 4 | 28 | 20 |
| 8 | 56 | 40 |
| 12 | 84 | 60 |
This tool counts Saturdays and Sundays as non-working and does not know about public holidays — there is no universal holiday calendar to draw from, so a "10 working days" estimate from here can still land a day or two off around Christmas, Easter or a local public holiday. Treat the working-days figure as calendar arithmetic, not a guarantee of business availability.
Adding months: the same day-doesn't-exist problem as ages
Add one month to 31 January and February has no 31st. Rather than rolling over into March the way JavaScript's raw date arithmetic would, this tool caps the result at the last real day of the target month — 31 January + 1 month lands on 28 February (or 29 in a leap year), not 3 March. The age calculator covers the same ambiguity from the other direction, for counting elapsed months rather than adding them.
Questions people ask
Does the working-days count remove public holidays?
No. It removes Saturdays and Sundays only. There is no single holiday calendar that applies everywhere, so building one in would make the figure wrong for anyone outside whichever country it assumed.
What does "inclusive" actually change?
It adds one day to the calendar-day result so that both the start and end dates are counted as days, rather than just the gap between them. It does not change the working-days count logic, which always counts each individual date once.
Can I subtract to get a date in the past?
Yes. Switch to "add or subtract from a date" and choose subtract — useful for working out something like "90 days before this invoice was due".
Why does adding 1 month twice not always match adding 2 months once?
It can differ right at month-end. 31 January + 1 month lands on 28 February; add another month from there and you reach 28 March. Adding 2 months to 31 January directly lands on 31 March instead, because the cap only applies when the day itself does not exist in the target month.