Week Number Calculator
Calculate the ISO 8601 week number for any date, or find the date from a week number.
Week Number
Calculate the ISO 8601 week number
Result
Date:
04/05/2026
Monday
Week:
Week 19 of 2026
Day:
1. Monday
Weeks in Year:
53
Week Range:
04/05/2026 → 10/05/2026
ISO 8601 defines Week 1 as the week containing the first Thursday of the year. Weeks start on Monday.