ISO Week Calculator
Calculate ISO 8601 week numbers and convert between dates and ISO week format.
Date to ISO Week
ISO Week to Date
Week 1, 2026
Dec 29, 2025 - Jan 4, 2026
About ISO Weeks
ISO 8601 defines weeks as starting on Monday. Week 1 is the week containing the first Thursday of the year. This means a year can have 52 or 53 weeks.
Thursday, May 28, 2026
W22
2026-W22-4
ISO Week Details
ISO Year2026
ISO Week22
ISO Day of Week4 (Thu)
Week RangeMay 25 - May 31
Weeks in 202653
Day Names (ISO)
Mon
1
Tue
2
Wed
3
Thu
4
Fri
5
Sat
6
Sun
7
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Editorial Note
MyCalcBuddy Editorial Team
This page is maintained as an educational calculator reference.
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Formula Source: Standard Mathematical References
by Various
🔄Last reviewed: May 2026
✓Formula checks are based on standard references and internal QA review.