ISO Week Number Pro

Convert dates to ISO week numbers and back. Find which week of the year any date falls in, per ISO 8601.

Date

Year

ISO week number (for reverse lookup)

Enter a date or a year + week number.

How to use

Enter a date to get its ISO week, or a year + week to get the dates.

What is an ISO week number?

ISO 8601 numbers each week of the year from 1 to 52 (or 53). Week 1 is the week containing the first Thursday of the year, and weeks start on Monday.

How do I convert a week number to a date?

Enter a year and ISO week number and the tool returns the Monday and Sunday dates of that week.

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