What is an ISO week number?

The ISO week number is defined by the ISO 8601 standard. Each week starts on Monday, and week 1 is the week with the year's first Thursday.

Why does the ISO week-year differ from the calendar year?

The ISO week-year can differ from the calendar year when a week spans across two years. For example, Dec 31 may fall into week 1 of the next ISO week-year.

Is this calculator timezone safe?

Yes. The tool uses timezone-safe calculations so results remain consistent regardless of your location.

Can I find the start and end dates of a week?

Yes. The tool shows the full Monday–Sunday date range for the chosen week.

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