Week Number (ISO 8601)
Pick a date to see its ISO 8601 week number, the week-year and the day of the year. Everything runs in your browser.
Uses the ISO 8601 standard (weeks start on Monday; week 1 contains the first Thursday). 🔒 Runs in your browser.
🔒 Tout se passe dans ton navigateur — rien n'est envoyé ni stocké.
Questions fréquentes
- How is the week number calculated?
- It uses the ISO 8601 standard: weeks start on Monday and week 1 is the week containing the first Thursday of the year.
- Why can early January be week 52 or 53?
- Under ISO 8601, the first days of January can belong to the last week of the previous year if they fall before that year's first Thursday.
- Is anything uploaded?
- No. The calculation runs entirely in your browser.