Week Number Calculator
Find the ISO week number for any date instantly. Also shows the week start and end dates, day of the week, and how many days remain in the week.
How to Use
- 1 Select any date using the date picker
- 2 Click Calculate to find the ISO week number
- 3 View the week number, year, week start (Monday), and week end (Sunday)
- 4 Use the copy button to share results
Use Cases
Many businesses report on a weekly basis using ISO week numbers — find the week number for any reporting period.
Reference sprint weeks or planning cycles by their ISO week number.
Determine which week number a pay period falls in.
Find the academic week number for any semester date.
FAQ
ISO 8601 defines weeks starting on Monday. Week 1 of a year is the week containing the first Thursday of the year, which means some days in early January may belong to the previous year's last week.
Because ISO week 1 is defined by the first Thursday rule, dates like December 29–31 may fall in week 1 of the next year, and January 1–3 may fall in the last week of the previous year.
Most years have 52 ISO weeks. Some years — called long years — have 53 weeks. This happens when January 1 or December 31 is a Thursday.
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