2027 has 52 ISO weeks.
Week 1 runs January 4 to January 10, and week 52 ends January 2. Weeks run Monday to Sunday, following ISO 8601.
- Weeks
- 52
- Week 1 starts
- January 4
- Week 52 ends
- January 2
- Standard
- ISO 8601
| Week | Starts (Monday) | Ends (Sunday) |
|---|---|---|
| 1 | ||
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| 52 |
Why 2027 has 52 weeks
Under ISO 8601 a week belongs to the year that contains its Thursday. That gives every year either 52 or 53 whole weeks and never splits one across a year boundary. A year gets 53 when it starts on a Thursday, or on a Wednesday in a leap year.
It is also why week 52 runs to Sunday, January 2, 2028, ending in the following year.
ISO weeks versus US week numbering
The two conventions disagree. ISO weeks start on Monday, and week 1 is the week holding the first Thursday. The common North American convention starts weeks on Sunday and calls the week containing 1 January week 1, which can produce a short first week. Payroll, retail, and broadcast calendars often use the latter. If a week number here disagrees with one from another system, this is usually why.
Week numbers by month
Each month page shows the ISO weeks it spans:
- January2027
- February2027
- March2027
- April2027
- May2027
- June2027
- July2027
- August2027
- September2027
- October2027
- November2027
- December2027
Other years
- 2026 week numbers — 53 weeks
- 2028 week numbers — 52 weeks
- 2029 week numbers — 52 weeks
- 2030 week numbers — 52 weeks