Is the week-of-year tool free?

Yes, completely free with no signup and no usage limits.

Does my data leave my device?

No. All calculations run in your browser. Nothing is sent to any server.

Yes. The tool is mobile-first and works on iPhone Safari and Android Chrome.

Look up ISO week numbers for any date, or enter a week number to see the Monday–Sunday date range. Also displays a full year week grid.

100% client-side · no upload

Pick a date

Year Week #

Year

Pick any date to instantly see its ISO week number, week start/end, and day of year.
Enter a year and week number to find the exact Monday–Sunday date range.
Use the full year grid to see all 52–53 weeks with their start dates at a glance.

Is the week-of-year tool free?: Yes, completely free with no signup and no usage limits.
Does my data leave my device?: No. All calculations run in your browser. Nothing is sent to any server.
Does it work on mobile?: Yes. The tool is mobile-first and works on iPhone Safari and Android Chrome.