Find the week number in a few simple steps.
Input the date you want to check.
Click calculate to find the week number.
Review the ISO week number and year.
ISO week numbers follow the ISO 8601 standard, where week 1 is the first week with at least 4 days in the new year, and weeks start on Monday.
Under ISO 8601, if January 1st falls late in the week, those days may belong to the last week of the previous year.
Yes, some systems start weeks on Sunday or define week 1 differently. This calculator uses the internationally recognized ISO 8601 standard.