Week Number Calculator
Find the ISO week number of any date.
Input
This tool runs entirely in your browser. The data you paste or load is never uploaded.
Result
Enter your input, then run the tool.
About this tool
Returns the ISO 8601 week number of a date, the Monday and Sunday of that week, the day of the year and how many weeks the year has. Week 1 is the week containing the first Thursday of January.
How to use it
- Pick a date, or leave it empty for today.
- Read the week number and the dates of that week.
Frequently asked questions
Why is 1 January sometimes in week 52 or 53?
ISO weeks start on Monday and week 1 must contain a Thursday, so the first days of January can belong to the last week of the previous year.
Do all years have 52 weeks?
No. Years starting on a Thursday, and leap years starting on a Wednesday, have 53 ISO weeks.
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