๐ ISO Week Date Converter
Convert between the ISO 8601 week date format (ISO year-week number-weekday, e.g. 2024-W01-1) and standard Gregorian calendar dates. Correctly handles week-spanning years, including years with a 53rd week.
How to use
- Choose "Date โ ISO week" or "ISO week โ Date".
- Enter a date, or an ISO year, week number, and weekday.
- The converted result is shown automatically.
FAQ
What is an ISO week date?
A date format defined by ISO 8601, where weeks start on Monday and week 1 is the week containing the year's first Thursday. A date is expressed as year-week-weekday (1=Monday to 7=Sunday), e.g. "2024-W01-1".
Why do some years have a 53rd week and others don't?
An ISO week-numbering year is either 364 days (52 weeks) or 371 days (53 weeks) long, depending on which weekday January 1st and December 31st fall on. Since this doesn't align exactly with the 365/366-day Gregorian year, some years end up with 53 ISO weeks.
Is the ISO week number the same as other week numbering systems?
Often close, but not necessarily identical. ISO 8601 has a precisely defined rule (Monday start, week 1 contains the first Thursday), while other regions or conventions may use different rules (e.g. Sunday start), so always check which system you need.