About this tool
Date Add / Subtract is a date calculator that shifts a start date forward or backward by a whole number of days, weeks, months, or years and returns the resulting calendar date together with its weekday. It runs entirely in your browser — no uploads, no accounts, no tracking — and works offline.
Pick a start date, type an amount, choose the unit, and set the operation to add or subtract. The calculation uses native JavaScript date arithmetic: a week counts as seven days, while month and year shifts follow the language's built-in rules, so a day that does not exist in the target month rolls into the following one. The answer is formatted in the page's language with the full weekday name.
The amount is read as an integer, so fractional values are truncated. To subtract you can either select the subtract operation or enter a negative amount — the two are equivalent. The start date is treated as a plain calendar date, with no time of day or time-zone conversion involved.