KW
Week Number Calculator
ISO calendar week of any date.
42
Week
2026
Year
Oct 12 – Oct 18, 2026
Week runs
53
Weeks in this year
Runs entirely in your browser. Nothing is sent anywhere.
How it works
- 1Enter your values.
- 2See the result update instantly as you type.
- 3Change any value to compare scenarios.
About this tool
Week Number Calculator: ISO calendar week of any date. Type your numbers and the result is calculated instantly — no button to press, nothing to install. All math runs locally in your browser, so the values you enter are never sent anywhere.
Example
| Input | |
|---|---|
| Date | 2026-10-13 |
| Result | |
| Week | 42 |
| Year | 2026 |
| Week runs | Oct 12 – Oct 18, 2026 |
| Weeks in this year | 53 |
How do I use the Week Number Calculator?
Enter your values. See the result update instantly as you type. Change any value to compare scenarios.
Is the Week Number Calculator free?
Yes. It is completely free with no sign-up, no usage limits and no watermark.
Is my data sent to a server?
No. Everything is calculated locally in your browser. Nothing you enter is uploaded, logged or stored.
Does it work on my phone?
Yes. It works in any modern browser on Android, iPhone, iPad, Windows, Mac and Linux — no app needed.