Date Calculator

The Date Calculator adds or subtracts a span of time from a starting date to find a resulting date, letting you move forward or backward by days, weeks, months, or years. Enter a base date, choose to add or subtract, specify the amount and unit, and it returns the exact calendar date that lands at the end of that interval.

It performs the arithmetic using true calendar rules: adding months advances the month field and clamps to the last valid day when the original day does not exist (for example, January 31 plus one month resolves to the end of February), and adding years respects leap years. This avoids the errors that come from naively adding fixed day counts, and it can combine several units in a single operation.

People reach for this tool to find due dates, project deadlines, contract expirations, warranty end dates, rent and billing cycles, and prescription refill dates. It is equally useful for working backward, such as determining when to start a task that must finish on a fixed date.

For predictable results, decide whether you want calendar months (which vary in length) or a fixed number of days, since those give different answers over long spans. If you instead need the number of days between two known dates, use the Days Between Dates tool, and to count down to a fixed future date use Days Until.