ISO Week Number Calculator
Identify the week index of any date. Select a date below to view week number, day of year, and day name.
Processed locally in your browser — nothing is uploaded.
How to Use
- Select a date.
- Click Calculate Week Details.
- Review the ISO week number and day index.
FAQ
What is an ISO week?
The ISO-8601 week starts on Monday, and Week 1 is defined as the week containing the first Thursday of the year.
How many weeks are in a year?
Most calendar years have 52 weeks, but some years (leap week years) have 53 weeks.