Week Number Calculator

Select Date

Week Number

Year

Calculation Standard

ISO 8601 (International)
Weeks start on Monday. First week has Thursday. US / North America
Weeks start on Sunday. First week has Jan 1st.

Week

Starts

Ends

Day of Year

%

Year Completed

Is Leap Year?

Date & Time

Calculate week numbers instantly. Find the ISO or US week number for any date, or determine the start and end dates for a specific week number.

Instant Calculation Private & Secure

Quick Tip

The ISO 8601 standard dictates that weeks start on Monday, and the first week of the year is the one containing the first Thursday.