2027 has 52 ISO weeks
2027 contains 52 ISO weeks. Week 1 opens on Monday, January 4, 2027 and week 52 closes on Sunday, January 2, 2028. That is 364 days of week numbering laid over a calendar year of 365 days, which is why the first and last weeks reach outside 2027 itself.
How many weeks are in 2027?
52. A year holds 52 whole weeks and one spare day, or two spare days in a leap year, so most years number 52 weeks and the spare days are absorbed by the weeks at either end. A year gets a 53rd week when those spare days line up so that a full extra Monday-to-Sunday block belongs to it. The test is short: a year has 53 ISO weeks when 1 January is a Thursday, or when it is a leap year beginning on a Wednesday. 1 January 2027 is a Friday and the year is not a leap year, so 2027 stops at 52 weeks. The next 53-week year is 2032.
Why the count is not simply 365 divided by 7
Dividing 365 by seven gives 52.143, which is not a whole number, so week boundaries cannot line up with year boundaries. ISO 8601 resolves this by numbering complete weeks and assigning each one to the year that holds most of its days, which is the same as the rule that week 1 is the week containing the first Thursday. The consequence is visible at both ends of 2027: week 1 runs January 4 to January 10, entirely inside the year, and week 52 runs December 27 to January 2, so it ends in 2028.
Week counts for nearby years
| Year | 1 January | Leap year | ISO weeks |
|---|---|---|---|
| 2024 | Monday | yes | 52 |
| 2025 | Wednesday | no | 52 |
| 2026 | Thursday | no | 53 |
| 2027 | Friday | no | 52 |
| 2028 | Saturday | yes | 52 |
| 2029 | Monday | no | 52 |
| 2030 | Tuesday | no | 52 |
| 2031 | Wednesday | no | 52 |
Long years are rare and unevenly spaced. Counting every year in a full 400-year Gregorian cycle gives 71 years with 53 weeks out of 400, which works out at roughly one year in 5.6. The gaps between them run to five, six or eleven years rather than repeating on a fixed interval, which is why payroll and retail calendars that use 52-week or 53-week years have to be checked rather than assumed.
The first and last weeks of 2027
| Week | Monday | Sunday | Spans a year end |
|---|---|---|---|
| Week 1 | January 4, 2027 | January 10, 2027 | no |
| Week 52 | December 27, 2027 | January 2, 2028 | yes |
Questions
- How many weeks are in 2027?
- 52 ISO weeks, running from January 4, 2027 to January 2, 2028.
- Does 2027 have a week 53?
- No, 2027 stops at week 52. The next 53-week year is 2032.
- Which week does 1 January 2027 fall in?
- Week 53 of 2026. 1 January 2027 is a Friday.
- How many days are in 2027?
- 365, because 2027 is a common year.
Browse the weeks
Other years
Weeks left in 2026 · Day of the year · What day is any date? · Event countdowns · When is it?