Time Zones & Calendar Suite

High-precision astronomical, religious, business, and standardization calendar converters.

ISO 8601 Week Number Calculator

ISO 8601 is the global standard for representing dates and times. It defines week 01 of any year as the week containing the first Thursday of that year, ensuring consistent week indices across business, logistics, and planning.

ISO Week Date String: 2026-W38-4
Bidirectional
Enter ISO 8601 ValuesTotal weeks in 2026: 52
Week Start: Sep 14, 2026Week End: Sep 20, 2026

Dynamic Conversion Output

ISO week date format (Y-W##-D)
2026-W38-4
Weekly Range Details
Week Starts (Mon)Sep 14, 2026
Week Ends (Sun)Sep 20, 2026
Total weeks in ISO year 2026:52 Weeks

Calendar Insights

  • • **ISO 8601** prevents "split weeks" at the start of a year. Week 01 always has a minimum of 4 days in the new calendar year.
  • • **First day**: The ISO week starts strictly on **Monday** and ends on **Sunday**.

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