📆 Week Calculator
Need to know the date a certain number of weeks from now (or before a past date)? This calculator adds or subtracts weeks from any date, and also shows the ISO week number for both the original and resulting date.
Add or subtract weeks from a date, and see its ISO week number.
How the Week Calculator works
The calculator adds (or subtracts) the number of weeks you enter as whole 7-day blocks, then reports the resulting date along with its ISO 8601 week number.
Step-by-step calculation
- 1Pick the start date.
- 2Enter the number of weeks to add or subtract.
- 3Each week is 7 days.
- 4Read the date and its ISO week number.
Worked example
January 5, 2026 plus 12 weeks is Monday, March 30, 2026 — ISO week 14.
Week Calculator examples
| Weeks added | New date |
|---|---|
| 1 | January 12, 2026 |
| 2 | January 19, 2026 |
| 4 | February 2, 2026 |
| 12 | March 30, 2026 |
| 52 | January 4, 2027 |
Start date: Monday, January 5, 2026. Other inputs kept at the calculator's default values. Results calculated by this calculator.
Why use a Week Calculator?
Plan schedules, pregnancies, projects and pay periods by weeks.
Important factors that can affect your results
- ISO weeks start on Monday; some calendars start on Sunday.
- Week 1 is the week with the year's first Thursday.
- Holidays are not skipped.
Frequently asked questions
What is an ISO week number?
It's the standardized week-of-year numbering (ISO 8601) used internationally — week 1 is the week containing the year's first Thursday.
Can I subtract weeks, not just add them?
Yes — enter a negative number to go backward from the date.
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Last reviewed November 2026 · How we build and check our tools · Report a problem