Add or Subtract Days
Find the date a number of days, weeks or months before or after another date.
Processing: This tool runs entirely in your browser. Your input and any file you open stay on your device — nothing is uploaded to a server.
How to use the add or subtract days
- Fill in the fields — they start with a worked example.
- Read the answer, and the arithmetic shown beneath it.
- Copy the results, or adjust the inputs to compare scenarios.
About this tool
Adding days is exact arithmetic. Adding months is not, because months have different lengths: one month after 31 January has no obvious answer. The convention used here — and by most calendar software — is to clamp to the last valid day, so 31 January plus one month gives 28 or 29 February rather than spilling into March.
The resulting weekday is shown, since a deadline that lands on a Saturday usually needs moving.
Common uses
- Setting a deadline a number of days out.
- Working out a contract end date.
- Finding the date a notice period expires.
Frequently asked questions
- What happens when I add a month to the 31st?
- It clamps to the last day of the target month, so 31 January plus one month is 28 or 29 February. That matches how most calendar software behaves.
- Can I go backwards?
- Yes — enter a negative number, or switch the direction.
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