How week number calculator works
The ISO 8601 standard numbers the weeks of a year from 1 to 52 (or 53). Week 1 is the week containing the first Thursday of the year, and weeks start on Monday. Because of this rule, dates near the turn of the year can belong to the last week of the previous year or the first week of the next.
This calculator finds the Thursday-nearest date for the input, counts the weeks from the first Thursday of that ISO year, and reports the ISO week and ISO year. It also reports the day of the week, the day of the year (1-366), and whether the year is a leap year.
Enter a date and the tool returns the ISO week number and ISO year, which together uniquely identify the week (written as 2024-W24). Use it for project planning, shift schedules, manufacturing week numbers, and European date conventions.