How it works
ISO 8601: Monday starts the week; week 1 contains January 4
Input definitions
- Date
- A complete Gregorian calendar date.
A worked example
- Date
- 2024-01-01
Assumptions & limits
Gregorian calendar dates at UTC midnight. Calendar-day arithmetic, not local elapsed hours. No holidays. End date excluded unless an inclusive option is selected.
Sources & review
Maintained by AnsRio. Methods and examples use automated checks; this does not imply independent professional certification.
Method updated 2026-10-17. Content checked against the stated method and examples. Our verification approach.
Common questions
Do daylight-saving changes affect calendar date results?
Date-only operations compare Gregorian calendar dates at UTC midnight. They do not count local elapsed hours. Timestamp operations require an explicit offset; individual tool assumptions state boundary rules.
How does the ISO week number tool work?
ISO 8601: Monday starts the week; week 1 contains January 4.
What are the assumptions and limits of ISO week number?
Gregorian calendar dates at UTC midnight. Calendar-day arithmetic, not local elapsed hours. No holidays. End date excluded unless an inclusive option is selected.