Add days to a date

Adding days to a date answers questions like "what date is 90 days from signing?" Pick a starting date, add days, weeks, months or years, and get the exact resulting date with its day of the week.

Worked example, counted on the calendar

Counting forward from Tuesday, 27 October 2026 — the day this site's examples were checked:

Each row is plain calendar counting: step forward one day at a time, rolling over month ends and leap days as they come. October has 31 days, so +30 days from 27 October crosses only four remaining October days before November begins — the tool does that bookkeeping for you.

Questions, answered

Is the starting day counted as day 1?

No — adding N days moves you N steps forward, so the starting day is day zero. "30 days from 27 October" is 26 November, the same answer a spreadsheet gives for date + 30. If a contract instead says "within 30 days, counting the day of signing", that is inclusive counting and the date falls one day earlier; the counting guide explains both.

What happens when I add months to the 31st?

The result clamps to the last day of the target month: 31 January + 1 month is 28 February (29 in a leap year). This matches how most contracts and billing systems treat monthly anniversaries, and it is stated here rather than hidden.

Can I add weeks or years instead?

Yes — switch the unit above. Weeks are exact multiples of 7 days; months and years use the clamping rule just described.