Date calculator
Count the days, weeks and working days between two dates, or add and subtract days, weeks, months and years from any date.
Days between
30 days
0 years, 0 months and 30 days.
- Weeks
- 4 w 2 d
- Working days
- 23
- Weekend days
- 8
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Two questions, two modes
Days between dates measures an interval. Add or subtract projects forward or backward from a known date. They sound similar and are used in very different situations - invoicing and notice periods need the first, deadlines and renewals need the second.
How the interval is measured
The elapsed time between two dates is converted to whole days and divided out. Because both dates are read at local midnight, daylight-saving transitions cannot shift the result by an hour and round the wrong way - a real bug in naive date arithmetic.
The calendar breakdown into years, months and days uses the same borrowing rules described on the age calculator: borrow the real length of the preceding month, then borrow twelve months from the year.
Working days
The working-day count walks the interval one day at a time and counts anything that is not a Saturday or a Sunday. Walking is slower than the modular arithmetic shortcut, but it is correct for every interval, including those starting or ending on a weekend - where the shortcut is off by one surprisingly often.
Between 1 July and 31 July 2026 there are 31 calendar days, of which 23 are working days and 8 fall on a weekend.
A worked example
From 1 March 2026 to 15 September 2026:
- Total days: 198
- Calendar breakdown: 6 months and 14 days
- Full weeks: 28 weeks and 2 days
- Working days: 142
Adding and subtracting
Adding days or weeks is unambiguous - it is straightforward arithmetic on the day count, and leap days are handled automatically.
Adding months or years is not. There is no universally agreed answer to “one month after 31 January”, and different software gives different results. This tool rolls overflow into the following month. If a date carries legal or financial weight, express the period in days instead, or check how the governing document defines it.
Where this gets used
- Payment terms. Net 30 from an invoice date, and whether that lands on a weekend.
- Notice periods. Counting a 90-day notice window precisely.
- Project planning. Working days available between a start and a deadline.
- Travel and visas. Days spent in a country against a 90-in-180 rule.
- Warranties and renewals. The exact expiry date two years after purchase.
Common questions
Does the working-days count include public holidays?
No. It excludes Saturdays and Sundays only, because public holidays differ by country, state and sometimes by industry. Subtract the holidays that apply to you from the result. For contractual deadlines, always check whether the agreement defines "business days" itself.
Why is adding one month to 31 January not 31 February?
There is no 31 February, so something has to give. This calculator follows the JavaScript date convention and rolls forward - 31 January plus one month gives 3 March in a non-leap year. Some systems clamp to the last day of the target month instead, giving 28 February. Neither is universally correct, so for legally significant dates prefer adding a fixed number of days.
Is the end date included in the count?
The day count is exclusive of the start and inclusive of the end - the interval between the two dates. From 1 March to 8 March is 7 days. The working-day count is inclusive of both endpoints, since it is answering "how many working days fall within this window".
Can I count backwards?
Yes. If the end date is earlier than the start date, the days-between mode reports the size of the interval and notes the reversal. For explicit backwards arithmetic use the subtract mode.
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