How to Use the Week Number Calculator
Enter any date, and the calculator returns its ISO 8601 week number (1 through 52 or 53), along with the year that week number belongs to — which can differ from the calendar year of the entered date for dates near the very start or end of the year.
The Week Number Calculator applies the ISO 8601 standard — here's what to enter and how to read the result.
Entering a date
Select any date, and the calculator returns its ISO week number instantly — useful for business planning, manufacturing schedules, or any context using week-based rather than date-based references.
Understanding the week-year
For dates in very late December or very early January, the displayed week's associated year can differ from the calendar year of the entered date, as covered in the ISO week guide — this is expected, correct behavior under the ISO standard, not an error.