# What is ISO week?

An ISO week is a week numbering system that starts on Monday. Week 1 is the week with the first Thursday of the calendar year. The format is YYYY-Www.

Every ScrollLaunch launch is filed under an ISO week such as 2026-W39. Year archive pages use that week year.

| Field | Value |
| --- | --- |
| term | ISO week |
| canonical | https://www.scrolllaunch.com/glossary/iso-week |
| kind | defined term |

## On ScrollLaunch

- [Week archive](https://www.scrolllaunch.com/week)
- [ISO week tool](https://www.scrolllaunch.com/tools/iso-week)