Date calculator — add or subtract days from a date
Add or subtract days, weeks, months and years from any date and get the exact result, with an optional business-days-only mode that skips weekends.
- Runs in your browser
- Nothing you enter is sent
- Free, no account
Pick a start date to see the resulting date.
How to add or subtract time from a date
- Set the start date — it defaults to today.
- Choose Add to date or Subtract from date.
- Fill in any mix of years, months, weeks and days, or tap a preset such as 30 days or 6 months.
- Switch on Business days mode when the offset should skip weekends — useful for "10 working days from receipt" style deadlines.
The step-by-step panel shows each intermediate date, so you can see exactly where a month-end clamp or a weekend skip changed the result.
The order of operations matters
Units are applied largest first: years, then months, then weeks, then days. That is the standard convention, and it matters at month boundaries. Starting from 31 January:
- Plus 1 month, then plus 1 day, gives 1 March (28 February, then one day).
- Plus 1 day, then plus 1 month, gives 1 March as well — but only by coincidence.
- Starting from 30 January the two orders diverge: 28 February plus a day is 1 March, while 31 January plus a month is 28 February.
Date arithmetic is not associative around month ends, so always state the order. This tool applies the standard order and prints it.
Month-end clamping
When the target month is too short for the day number, the result is clamped to the last day of that month. This is the behaviour of essentially every date library, spreadsheet and contract drafting convention.
| Start date | Operation | Result |
|---|---|---|
| 31 January 2027 | + 1 month | 28 February 2027 |
| 31 January 2028 | + 1 month | 29 February 2028 (leap year) |
| 31 March 2026 | − 1 month | 28 February 2026 |
| 29 February 2028 | + 1 year | 28 February 2029 |
| 31 May 2026 | + 3 months | 31 August 2026 |
Note the asymmetry: 31 January plus one month is 28 February, but 28 February minus one month is 28 January, not 31 January. Clamping is not reversible, which is why long chains of month arithmetic should always be computed from the original start date rather than step by step.
Business days mode
In business-days mode only Monday to Friday are counted. The start day itself is never counted, so "3 business days from Monday" is Thursday. If the start date lands on a weekend the count begins from the following Monday. Public holidays are not applied here — the business days calculator handles those, with a holiday list you can maintain.
Frequently needed offsets
| Offset | Where it shows up |
|---|---|
| 14 days | EU consumer right to cancel an online order |
| 30 days | Standard invoice payment terms, notice periods |
| 45 and 180 days | US 1031 exchange identification and closing windows |
| 90 days | Schengen and many visa-free stay limits, probation periods |
| 180 days | Passport validity commonly required for entry |
| 280 days | Estimated due date from the last menstrual period |
Rules that are quoted in days are almost always counted excluding the start date. Where a rule says "within X days of", read the source carefully — some count clear days, some count business days.
Questions
What does "31 January plus one month" give?
28 February (29 in a leap year). When the target month has no matching day number the result is clamped to the last day of that month, which is the standard convention in contracts and in every major date library.
In what order are the units applied?
Years first, then months, then weeks, then days. Order matters at month ends, so the tool shows each intermediate date in the working-out panel.
What does business-days mode do?
It counts only Monday to Friday, so "10 business days from Thursday" lands two weeks later on the Thursday. From a Saturday or Sunday, the first business day counted is the Monday.
Can I count backwards?
Yes — choose Subtract, or enter negative numbers. Both give the same result and the working-out panel spells out the direction.