Add or Subtract Days
Add or subtract days, weeks, months or years from any date and get the resulting date, with the weekday shown.
How it works
Adding days is a straight calendar walk — the tool moves forward or back the number you give and reports where it lands, including the weekday, which is usually what the question is really about.
Adding months is not the same as adding 30 days, and it can be ambiguous. 31 January plus one month has no 31 February to land on, so the result clamps to the last day of the month. Different systems resolve this differently; this one clamps, which is the common convention.
For deadlines counted in working days rather than calendar days, use the business days calculator instead — 30 days and 30 working days are six weeks apart.
The formula
Add days
result = start date + n days
Add weeks
result = start date + (n × 7) days
Add months
same day number in the target month
Clamped to the last day when that date does not exist.
Worked examples
| Scenario | Working | Result |
|---|---|---|
| 1 Jan 2025 plus 90 days | Calendar walk | 1 Apr 2025, a Tuesday |
| 31 Jan plus 1 month | No 31 Feb | 28 Feb (clamped) |
| Today minus 30 days | Backwards walk | The date a month ago |
When you'd use it
- Working out a payment or notice deadline
- Finding a date a fixed period after an event
- Checking what day of the week a future date falls on
- Backdating from a due date
Common 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 February (29 in a leap year). There is no universally right answer here — some systems roll over to 3 March instead — so check what your contract or system expects.
Is adding 30 days the same as adding a month?
Only in a 30-day month. Adding 30 days to 1 January gives 31 January; adding a month gives 1 February. Legal and financial deadlines usually mean one or the other specifically, so it is worth checking which.
Can I add working days instead?
Use the business days calculator for that. It skips weekends and any holidays you list, which is what most contractual deadlines actually mean.