WEEK NUMBER
CALCULATOR

Calculate ISO week numbers for any date. Find which week of the year any date falls in with ISO 8601 standard compliance.

CURRENT WEEK

WEEK 0

2025

SELECT DATE

• Week 1 is the first week with at least 4 days in the new year

• Weeks start on Monday and end on Sunday

• A year can have 52 or 53 weeks

• January 1st can be in week 1 of the current year or week 52/53 of the previous year

New Year's DayWeek 1

Independence Day (US)Week 27

Christmas DayWeek 52

New Year's EveWeek 1

WEEK NUMBERCALCULATOR