How to use it
- Choose the start date (it starts as today).
- Choose Add or Subtract and enter any combination of years, months, weeks and days.
- Turn on business days if the days should skip Saturdays and Sundays, then read or copy the resulting date.
How it works
Years and months are added first, together, and then weeks and days. Months are calendar months, not 30-day blocks: 15 March + 1 month is 15 April. When the target month is too short for the start day, the date moves to the last day of that month, so 31 January + 1 month is 28 February (29 February in a leap year) and 29 February 2024 + 1 year is 28 February 2025. A note appears whenever this happens.
Because of this rule, adding 1 month twice can differ from adding 2 months once: 31 January + 1 month = 28 February, and + 1 more month = 28 March, while 31 January + 2 months = 31 March. Weeks are always exactly 7 days.
With business days on, the days field counts Monday to Friday only: from a Friday, 1 business day later is the following Monday. Weekends are skipped but public holidays are not, because they depend on the country and the organisation. Weeks still count as 7 calendar days.
The result is shown in your local date format, with the weekday and the ISO 8601 date (YYYY-MM-DD), which is unambiguous in any country.
Examples
90 days from today
From 22 October 2026, adding 90 days gives Wednesday 20 January 2027, ISO date 2027-01-20.
Payment terms in business days
An invoice dated Thursday 22 October 2026 with 10 business days to pay is due on Thursday 5 November 2026 (weekends skipped, holidays not).
End of month
A monthly subscription started on 31 January 2025. Adding 1 month gives 28 February 2025; adding 2 months to the start date gives 31 March 2025.
Frequently asked questions
What is 31 January plus one month?
28 February, or 29 February in a leap year. When the day does not exist in the target month, the last day of that month is used. Many spreadsheet programs (for example EDATE) follow the same rule.
Is adding 1 month the same as adding 30 days?
No. A month here is a calendar month, so its length depends on the dates (28 to 31 days). If you need exactly 30 days, put 30 in the Days field.
Does the business days option skip public holidays?
No, only Saturdays and Sundays are skipped. Holidays vary by country, region and employer, so add extra days for any that fall in the period.
Does the start date count as day 1?
No. Adding 1 day to Monday gives Tuesday. If your rule says the start day counts, subtract one day from the number you enter.
Privacy
The calculation runs entirely in your browser. Dates are not sent or stored.