Add / Subtract Days, Weeks & Months

Add or subtract days, weeks, months, or years from any date to find exactly what date you land on.

Adding or subtracting a span of time from a date sounds like it should be simple counting, and for days, it mostly is — but the moment you're adding months or years instead, the calculation stops being simple arithmetic, because months don't all have the same number of days, and adding "one month" to January 31st doesn't have an obviously correct answer, since February doesn't have 31 days.

That ambiguity is exactly why this kind of calculation benefits from software handling it consistently rather than everyone applying their own ad hoc rule for edge cases like month-end dates or leap years — a date library resolves the February 31st problem the same way every time, which matters if you're relying on the answer to be predictable rather than just "reasonable."

This tool handles the addition and subtraction directly across days, weeks, months, or years: pick a starting date, choose an amount and a unit, and it calculates the resulting date using consistent date arithmetic that correctly handles different month lengths and leap years — useful for anything from "what date is 90 days from now" to "what was the date exactly six months before this one."

1. Pick a starting date.
2. Enter an amount and choose the unit.
3. Choose add or subtract, then press Calculate.