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
Enter the required date or time, adjust the options, then run the Week Number Calculator for a clear copyable result.
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.
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.