Week Number Calculator
Use the Week Number Calculator to find the ISO week number and week-year for a date quickly on mobile or desktop.
Week Number Calculator
Tool inputs are not stored, and private values stay out of analytics.
Result
How it works
The tool works by using the ISO 8601 rule where weeks begin Monday and week one contains the first Thursday. Processing stays in the browser, and entered date or time values are not stored or sent to analytics.
Helpful details
Quick guide for better results
Use this focused page to complete one everyday task quickly and clearly.
When this page is useful
Week Number Calculator is built for one clear task, so you can get a result without leaving the page or creating an account.
- Finish a common task without sign-up.
- Get a clear copyable result.
- Use examples and FAQs to check the outcome.
How to get a clearer result
Enter only the values needed by the tool and review the output before relying on it.
- Check your inputs.
- Review units or formats.
- Use examples when unsure.
Common mistakes before relying on the result
Relying on a result without reviewing the entered values can cause mistakes.
- Review values first.
- Do not use it alone for critical decisions.
- Copy the result only after checking it.
What happens to your input
Inputs are processed in the browser whenever possible and private values are not stored.
- No account is required.
- Private values are not saved.
- Analytics do not store tool inputs.
Examples
Practical example
January 1, 2026 is in ISO week 1 of 2026.
Accuracy note
Check the time zone and date format when comparing a result with another system.
FAQ
How do I use the Week Number Calculator?
Enter the requested values, review the options, then calculate and read the result.
Are entered dates or times stored?
No. The calculation runs in the browser and input values are not stored.
Does it work on mobile?
Yes. The controls and results are designed for phones and desktop browsers.