ISO week number
Pick a date — get ISO week number, ISO week-year, and day of week.
Why ISO weeks are used
ISO week numbers are common in planning systems, manufacturing reports, and sprint schedules because they create a stable week count across years. That is helpful when a project is tracked as 2026-W22 instead of a month-based label that can move around.
Edge cases around New Year
The first few days of January do not always belong to week 1, and the last few days of December may belong to the next week-year. That edge case is exactly why this tool is useful when calendar dates and reporting weeks do not line up neatly.
Planning with ISO weeks
Manufacturing and enterprise reporting often label releases as 2026-W22 instead of calendar months — ISO weeks align weeks cleanly for sprint planning.
ISO rules
Week one contains the first Thursday of the Gregorian year — early January dates may belong to prior week-year.
Reporting cycles
Finance and operations teams label weeks as 2026-W14 instead of mid-April dates to align reports across regions. ISO week numbers remove ambiguity when month boundaries split a work sprint.
Quick start
- Pick a date — Select any calendar date you need to map to an ISO week.
- Read ISO week number — See week number, ISO week-year, and weekday — note early-January edge cases.
- Compare with calendar week — Remember ISO week 1 contains the year's first Thursday, not always January 1.