About this calculator
Months and years are added on the calendar, so 31 January plus one month gives 28 or 29 February.
How to use it
- Enter the start date.
- Choose add or subtract.
- Enter the number and choose days, weeks, months or years.
The formula
Result = start date ± n days (or weeks, months, years)
- weeks
- 7 days each
- months
- calendar months, clamped to the month’s last day
Worked example
90 days after 3 October 2026
- 3 October 2026 + 90 days = 1 January 2027, a Friday.
What the result means
For working days only, use the business days calculator.
Assumptions
- Gregorian calendar.
Limitations
- Public holidays are not skipped.
Frequently asked questions
What is 90 days from today?
Enter today and 90 days; the calculator shows the date and weekday.
Does a 30-day notice include the first day?
It depends on the contract; this calculator counts the start date as day 0.
What happens with 31st plus one month?
You get the last day of the next month.
Last reviewed on 3 October 2026. Found a mistake? Tell us.