Week Number

Find the ISO week number for any date. Based on the ISO 8601 standard, this calculator helps with project planning, scheduling, and calendar management.

Select a date to find the ISO 8601 week number

Frequently Asked Questions

How is the week number determined?
Week numbers follow the ISO 8601 standard, which defines Monday as the first day of the week. Week 1 is the week containing the first Thursday of the year.
How many weeks are in a year?
Most years have 52 weeks, but some years have 53 weeks. The calculator also shows the total number of weeks for the selected year.
Do different countries use different week numbering systems?
Yes, some countries start the week on Sunday. This calculator uses the ISO 8601 international standard, which starts weeks on Monday.
2026 calendar data