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Week Number Calculator
Find the week number.
Get the ISO week number for any date, or find the date range for a given week and year.
Date to Week
Find which ISO week number any date falls in.
Week to Date Range
Find the Monday-to-Sunday date range for a given week number.
Free & Unlimited
No signup, no watermarks, no limits. Use it as many times as you like.
What is a Week Number Calculator?
A week number calculator tells you which numbered week of the year a date falls in, using the ISO 8601 standard (weeks start on Monday, and week 1 is the first week with at least 4 days in the new year). It also works in reverse, converting a week number and year into the actual Monday–Sunday date range.
Frequently Asked Questions
The ISO 8601 standard defines Monday as the first day of the week and week 1 as the week containing the year's first Thursday, ensuring every week has a majority of its days in the correct year.
Yes. Depending on which day of the week January 1st falls on and whether it's a leap year, a year can have either 52 or 53 ISO weeks.
Yes. 100% free — no account required, no watermarks, no usage limits.