Is ISO Week Calculator free?

Yes, ISO Week Calculator is completely free to use with no signup required.

Does ISO Week Calculator send my data to a server?

No. ISO Week Calculator runs entirely in your browser using client-side JavaScript. Your data never leaves your device.

Determine standard ISO-8601 week formats and calendar years for dates. Operates offline in your browser.

DevTab

Never leaves your browser

Determine the standard ISO-8601 week number and year for any selected date client-side.

Select Calendar Date

ISO Week String Output

2026-W35

Week Number: 35

ISO Year: 2026

ISO Week ComputedISO representation: 2026-W35