Calculateur de Numéro de Semaine Gratuit en Ligne

ISO 8601 defines week 1 as the week containing the year's first Thursday. Weeks run Monday–Sunday. This means January 1 might be in week 52 or 53 of the previous year if it falls on a Friday, Saturday, or Sunday.

If January 1 falls on a Saturday or Sunday, the Thursday of that week is in December. So that week belongs to the previous ISO year. January 1, 2022 was a Saturday — so it was in ISO week 52 of 2021.

Most years have 52 ISO weeks. Years where January 1 or December 31 is a Thursday have 53 ISO weeks (this happens roughly 5-6 times per decade).

Not always. US businesses often count week 1 as the week of January 1 (regardless of day), starting Sundays. This differs from ISO 8601. Always clarify which standard is being used when scheduling across regions.

Open the tool and click Today to see the current ISO week number. Week numbers change on Monday UTC.

Yes, the Calculateur de Numéro de Semaine on Allio Tools is completely free with no sign-up or registration required. It works directly in your browser.

Trouvez le numéro de semaine ISO de n'importe quelle date de l'année. No data is sent to a server — everything runs locally in your browser for maximum privacy and speed.

No installation needed. The Calculateur de Numéro de Semaine runs entirely in your web browser on any device — desktop, tablet, or mobile.

Completely safe. The Calculateur de Numéro de Semaine processes everything locally in your browser. No input data, results, or usage information is ever transmitted to or stored on any server.

After the page loads for the first time, the Calculateur de Numéro de Semaine works without an internet connection for all client-side processing. Tools that fetch live external data (such as DNS or network lookups) require an active connection.

Yes. The Calculateur de Numéro de Semaine uses your browser's built-in time zone data, which includes daylight saving time rules for all supported time zones, keeping results accurate year-round.

The Calculateur de Numéro de Semaine uses your browser's built-in Intl and Date APIs, which automatically account for daylight saving time transitions, leap years, and regional time zone rules. You do not need to make any manual adjustments for these calendar events.

Yes. The Calculateur de Numéro de Semaine is built with standard browser APIs and works on all modern browsers including Chrome, Firefox, Safari, and Edge — on both desktop and mobile. No plugins, extensions, or third-party software are required.

Select and copy the result text to paste into any document or app. For image tools, a Download button saves the file directly to your device. Your browser's built-in screenshot function also captures results quickly. No account or login is required.