Date calculator
Add or subtract days, weeks, months, years or working days to a date, and count the working days between two dates.
How to use
Choose A date plus or minus a period to add or subtract days, weeks, months, years or working days, or Working days between two dates to count them. The result updates as you change anything: the date with its weekday, how many calendar days away it is and its ISO week, or the working days, calendar days and weekend days of the period.
Months and years keep the day of the month: 15 March plus one month is 15 April. When that day does not exist, the result is the last day of the month, so 31 January 2026 plus one month is 28 February 2026, and 29 February in a leap year such as 2028. Adding one month to 31 January by moving the month number alone, as plain JavaScript dates do, overflows into 3 March instead.
Adding working days does not count the start date and skips the weekend and any holidays you list, as the WORKDAY function of spreadsheets does: 10 working days after Friday 6 November 2026 is Friday 20 November. Counting the working days between two dates includes both of them, as NETWORKDAYS does, and is negative when the end comes before the start. The weekend can be Saturday and Sunday, Friday and Saturday, Sunday only, or none.
Public holidays differ by country and often by region, so the calculator has none built in: type them one per line as YYYY-MM-DD or pick them with Add a holiday. They stay on this page and are not saved. Dates are counted as calendar days, so clock changes never shift a result. In Excel the same calculations are WORKDAY, NETWORKDAYS and EDATE.
Example
31 January 2026 + 1 month28 February 2026: February has no 31st, so the result is its last day. From 31 January 2028 it is 29 February 2028, a leap year.10 working days after Friday 6 November 2026Friday 20 November 2026: the start date does not count and two weekends are skipped.Working days from 1 October 2012 to 1 March 2013110, counting both dates, and 107 with 22 November 2012, 4 December 2012 and 21 January 2013 as holidays: the figures of Microsoft’s NETWORKDAYS example.2 November 2026 + 90 daysSunday 31 January 2027, in ISO week 4 of 2027.
Frequently asked questions
Does the start date count?
When adding, no: one day after Friday is Saturday, and one working day after Friday is Monday. When counting the working days between two dates, both dates count. If a contract or a law sets a deadline, check how it counts: some rules start the next day, others exclude the last day.
What is 31 January plus one month?
The last day of February: 28 February, or 29 in a leap year. The calculator never moves into the next month, which is what happens if the day is simply kept and the month number increased.
Does it know public holidays?
No. Holidays depend on the country and often the region, so add your own; each one only counts when it falls on a working day.
Which weekend should I choose?
Saturday and Sunday in most of the world. Choose Friday and Saturday or Sunday only where the working week is different, or No weekend to count every day.
How do I do this in Excel?
=WORKDAY(start, days, holidays) adds working days, =NETWORKDAYS(start, end, holidays) counts them with both dates included, and =EDATE(start, months) adds months.