About the Date Add/Subtract Calculator
The Date Calculator finds the date a set period before or after a starting date. Enter a start date, choose to add or subtract, and specify any combination of years, months, weeks and days. It is ideal for working out deadlines, contract end dates, due dates, notice periods, return-by dates and "what date will it be in N days" questions.
How date arithmetic works
Years and months are applied as calendar units first, then weeks and days are added as fixed 7-day and 1-day steps. Because months vary in length, adding one month to 31 January lands on the last valid day of February. The calculator handles month-end roll-over and leap years for you.
Business-days mode
Tick business days only to count the days field in working days — Monday to Friday — skipping weekends. This is useful for shipping estimates, SLA windows and notice periods stated in working days. Note that it does not subtract public holidays, which vary by country.
Example
Adding 90 days to 2 June 2026 gives 31 August 2026, a Monday. In business-days mode, 90 working days from the same start lands much later because weekends are skipped.
Frequently Asked Questions
How do I add days to a date? Enter the start date, keep the operation on "Add", type the number of days and press calculate.
What happens when I add a month to the 31st? If the target month has fewer days, the result rolls to that month's last day, then continues normally.
Does business-day mode remove holidays? No — it removes weekends only. Public holidays differ by country and are not deducted.
Related Calculators
- Date Difference Calculator — Exact gap between two dates.
- Days Until Calculator — Countdown of days to a future date.
- Age Calculator — Exact age in years, months and days.
- Time Duration Calculator — Duration between two times, plus add and subtract hours, minutes and seconds. Decimal-hours output for timesheets.