ISO week dates
When Is Week 1? Dates & Calendar
Today: · Eastern Time (America/New_York)
Week 1 dates
Week 1 of 2026
Week 1 of 2026 runs from Monday, December 29, 2025 through Sunday, January 4, 2026.
- Relevant ISO year
- 2026
- Weeks in this ISO year
- 53
- Today’s ISO week / year
- 43 / 2026
Week 1 of 2026
Each of the seven selected dates is labeled Week 1.
December 2025
| Mon | Tue | Wed | Thu | Fri | Sat | Sun |
|---|---|---|---|---|---|---|
| Week 1 | Week 1 | Week 1 |
January 2026
| Mon | Tue | Wed | Thu | Fri | Sat | Sun |
|---|---|---|---|---|---|---|
| Week 1 | Week 1 | Week 1 | Week 1 | |||
Week 1 by ISO year
| ISO year | Monday — start | Sunday — end |
|---|---|---|
| 2024 | Mon, Jan 1, 2024 | Sun, Jan 7, 2024 |
| 2025 | Mon, Dec 30, 2024 | Sun, Jan 5, 2025 |
| 2026 | Mon, Dec 29, 2025 | Sun, Jan 4, 2026 |
| 2027 | Mon, Jan 4, 2027 | Sun, Jan 10, 2027 |
| 2028 | Mon, Jan 3, 2028 | Sun, Jan 9, 2028 |
| 2029 | Mon, Jan 1, 2029 | Sun, Jan 7, 2029 |
| 2030 | Mon, Dec 31, 2029 | Sun, Jan 6, 2030 |
| 2031 | Mon, Dec 30, 2030 | Sun, Jan 5, 2031 |
| 2032 | Mon, Dec 29, 2031 | Sun, Jan 4, 2032 |
| 2033 | Mon, Jan 3, 2033 | Sun, Jan 9, 2033 |
| 2034 | Mon, Jan 2, 2034 | Sun, Jan 8, 2034 |
Quick answers
- How many weeks are in 2026?
- 2026 has 53 ISO weeks. Week 53 does not occur every year.
- What week is it today?
- Today is in ISO week 43 of 2026.
How this is calculated
- ISO weeks run Monday through Sunday. Week 1 contains January 4 (the first Thursday of the year).
- The relevant year is the ISO week-year of today in Eastern Time (America/New_York). Near New Year, it can differ from the calendar year.
- An ISO year has 52 or 53 weeks. Week 53 exists only in applicable ISO years; it is never rolled into Week 1.