ISO 8601 calendar

ISO Week Number Calculator

See which ISO week contains a date, including year-boundary dates.

✓ Your time and date calculations are not stored.

Result

Your result will appear here.

How it works

Find the ISO week number, week-year, start and end for any date. Inputs are validated and calculations use PHP’s calendar and IANA time-zone support.

Example

Choose realistic dates or zones, calculate, then copy or bookmark the resulting URL. The query values make a calculation easy to revisit without storing it in an account.

Frequently asked questions

Are my inputs saved?

No. Calculator inputs are processed for the immediate result and are not written to a user database.

Does this account for daylight saving time?

Time-zone calculations use named IANA zones, so the rules for the selected date are applied.