Add or Subtract Dates Calculator
Add or subtract days, weeks, months or years from a date.
Assumptions used in this calculation
- Calendar: Uses the Gregorian calendar; month and year arithmetic accounts for variable month lengths and leap years.
About this calculator
Figuring out "90 days from now" or "6 months before this deadline" by counting forward on a calendar is tedious and easy to miscount, especially once the span crosses a month with a different number of days or a leap year. This calculator adds or subtracts a chosen number of days, weeks, months or years from a starting date, using proper calendar arithmetic that correctly handles variable month lengths and month-end rollovers, and returns the resulting date along with its day of the week. It's useful for calculating a payment or contract due date, a return-by or expiry date, a follow-up appointment, or any deadline defined as a fixed offset from a known date, without the risk of a manual counting error creeping into something that matters.
Worked example
Add 30 days to 1 Jan 2026
Result: 31 Jan 2026
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