Week Number Calculator
Find the current ISO 8601 week number, look up week numbers for any date, and find date ranges for any week of the year.
Current Week
Week 43
of 53 weeks in 2026
Week Starts (Monday)
2026-10-19
Sunday
Week Ends (Sunday)
2026-10-25
Saturday
Day of Year
292/365
Day of Week
Monday
Weeks in Year
53
Weeks Remaining
10
About ISO 8601 Week Numbers
ISO 8601 is the international standard for date and time representation. Under this standard, weeks start on Monday and end on Sunday.
Week 1 of a year is the week that contains the first Thursday of the year (equivalently, the week containing January 4). This means some years have days from late December counted as week 1 of the next year.
Most years have 52 weeks, but some years have 53. A year has 53 ISO weeks if it starts on a Thursday (common year) or Wednesday (leap year), or if it's a leap year starting on a Thursday.