Week number
Pick a date: its week number appears, with the dates from Monday to Sunday. January 1, 2026, a Thursday, is in week 1.
- Checked on thousands of cases
- Sources: ISO
- Updated November 6, 2026
Week
From Monday, November 2, 2026 to Sunday, November 8, 2026
2026 has 53 weeks.
Dates of a week
From Monday, November 2, 2026 to Sunday, November 8, 2026
How it works
Formula: Week 1 = the week (Monday–Sunday) that contains January 4
The tool follows the ISO 8601 standard, used in Europe and in business: weeks start on Monday, and week 1 is the week with the year's first Thursday, so it always contains January 4. The first days of January can therefore belong to the last week of the previous year, and the last days of December to week 1 of the next. A year has 52 or 53 weeks.
Worked examples
November 6, 2026
Week 45, from November 2, 2026 to November 8, 2026.
January 1, 2027
Week 53 of 2026: this day still belongs to the last week of the previous year.
Number of weeks in 2026
53 weeks.
Common mistakes
Starting week 1 on January 1.
Week 1 is the week of the first Thursday: in 2026 it starts on December 29, 2025.
Thinking a year always has 52 weeks.
2026 has 53.
Mixing it up with US week numbering (weeks starting on Sunday).
ISO week numbers start on Monday; many US calendars count differently.
What the calculation leaves out
- ISO 8601 numbering. Many US calendars start weeks on Sunday and count week 1 from January 1, so their numbers can differ.
Number of weeks and start of week 1
| Year | Weeks | Start of week 1 |
|---|---|---|
| 2026 | 53 | December 29, 2025 |
| 2027 | 52 | January 4, 2027 |
| 2028 | 52 | January 3, 2028 |
| 2029 | 52 | January 1, 2029 |
| 2030 | 52 | December 31, 2029 |
| 2031 | 52 | December 30, 2030 |
Frequently asked questions
How many weeks are in a year?
52 or 53. A year has 53 weeks when it starts on a Thursday, or on a Wednesday in a leap year.
Why is January 1 sometimes in week 52 or 53?
Because week 1 is the week of the first Thursday: if January 1 falls on a Friday, Saturday or Sunday, it still belongs to the last week of the previous year.
Which standard do calendars use?
In Europe and in most business software, ISO 8601: weeks run Monday to Sunday. US wall calendars often start on Sunday.