Week of Year Converter
Knowing the week number of a date powers sprint planning, payroll periods and reporting. This converter returns the year-week string (e.g. `2026-W33`) using the ISO week numbering that most business tools follow.
Paste any date and read off its week number, ISO year and the week's start/end dates — no more counting weeks on a calendar.
Week of Year Converter Quick Reference
| Format | Pattern / Description | Example 1 | Example 2 |
|---|---|---|---|
| Week of Year | ISO Week | 2026-W33 | 2026-W01 |
* Examples are rendered in UTC for the fixed sample instants above.
When to Use Week of Year
Sprint & milestone planning
Convert milestone dates to week numbers for team schedules and board labels (Sprint 33 → W33).
Payroll & billing periods
Assign expenses and timesheets to the correct week number across month boundaries.
Reporting buckets
Group analytics by ISO week number for consistent weekly reporting regardless of month start.
Frequently Asked Questions
What is the week number of a date?
The ISO week number (1–53) with its ISO year, written `YYYY-Www`. 2026-08-13 is week 33 of 2026 (`2026-W33`).
What day does the week start on?
ISO weeks run Monday to Sunday. US-style weeks start Sunday and yield different week numbers for the same date.
Which week is week 1?
The week containing the first Thursday of the year is week 1, which may start in the previous calendar year.
Why is my week number different from Excel's?
Excel has two systems: `WEEKNUM(...,21)` is ISO; the default is US-style. Use 21 for ISO week numbers.
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