Calendar Week
Choose a date to see its ISO calendar-week details, calculated locally without a server timezone.
Choose a date to calculate its calendar details.
Monday–Sunday week view
| Weekday | Date |
|---|
ISO 8601: weeks run Monday–Sunday. Week 1 contains January 4 (the year’s first Thursday). The ISO week-year can differ from the calendar year. Date-only UTC calendar arithmetic avoids timezone and daylight-saving shifts.
A QUICK WALKTHROUGH
How to use this tool
- Choose a calendar date.
- Calculate the ISO week and date details.
- Review the week-year and the full Monday–Sunday week.
ISO week convention
Weeks begin on Monday; week 1 contains January 4. The week-year follows the Thursday of the selected week, so year boundaries can differ from the calendar year.
Date-only calculation
The tool treats your selected date as calendar fields and performs UTC arithmetic locally. It does not convert the date into a server or device timezone.
GOOD TO KNOW
Common questions
Why does January sometimes show the previous year?
Early January can belong to the previous ISO week-year; late December can belong to the next one.
Is Sunday the first day?
No. This tool consistently uses the ISO Monday–Sunday convention.