Date → week
Enter any date.
Free calculator
Week number calculator
Convert a date to ISO and US-style week numbers, or convert an ISO week back to a date range.
ISO week → date
Enter an ISO week number and week-year.
Why ISO and calendar years can differ
Around New Year, a date can belong to an ISO week-year different from its calendar year. The calculator applies the ISO 8601 rules automatically and also shows the simplified Sunday-start US-style comparison for date inputs.
Read the ISO guide →