Week Numbers 2027
2027 has 52 numbered weeks under ISO 8601 and 53 under the US convention. Week 1 starts on Monday 4 January 2027 and week 52 ends on Sunday 2 January 2028.
Today in UTC.
Weeks run Monday to Sunday. Week 1 holds the first Thursday.
Week number now
of 52 in 2027 · ISO 8601 numbering
Monday 4 January 2027 is in week 1 of 2027 under ISO 8601 numbering. That week runs from Monday 4 January 2027 to Sunday 10 January 2027.
The two conventions disagree on this date. US numbering makes it week 2 of 2027. Check which one the system you are filling in uses, because a week number without its convention is not a complete answer.
Show the working
| Date | 2027-01-04 |
|---|---|
| Weekday | Monday |
| ISO week 1 starts | 2027-01-04 |
| US week 1 starts | 2026-12-27 |
| This week runs | 2027-01-04 to 2027-01-10 |
| Weeks in 2027 | 52 weeks |
Every week of 2027
ISO 8601 weeks, running Monday to Sunday. Week 1 is the week holding the first Thursday of the year, which is why it can start in the previous December.
| Week | Starts | Ends | ISO dates |
|---|---|---|---|
| Week 1 | 4 January 2027 | 10 January 2027 | 2027-01-04 to 2027-01-10 |
| Week 2 | 11 January 2027 | 17 January 2027 | 2027-01-11 to 2027-01-17 |
| Week 3 | 18 January 2027 | 24 January 2027 | 2027-01-18 to 2027-01-24 |
| Week 4 | 25 January 2027 | 31 January 2027 | 2027-01-25 to 2027-01-31 |
| Week 5 | 1 February 2027 | 7 February 2027 | 2027-02-01 to 2027-02-07 |
| Week 6 | 8 February 2027 | 14 February 2027 | 2027-02-08 to 2027-02-14 |
| Week 7 | 15 February 2027 | 21 February 2027 | 2027-02-15 to 2027-02-21 |
| Week 8 | 22 February 2027 | 28 February 2027 | 2027-02-22 to 2027-02-28 |
| Week 9 | 1 March 2027 | 7 March 2027 | 2027-03-01 to 2027-03-07 |
| Week 10 | 8 March 2027 | 14 March 2027 | 2027-03-08 to 2027-03-14 |
| Week 11 | 15 March 2027 | 21 March 2027 | 2027-03-15 to 2027-03-21 |
| Week 12 | 22 March 2027 | 28 March 2027 | 2027-03-22 to 2027-03-28 |
| Week 13 | 29 March 2027 | 4 April 2027 | 2027-03-29 to 2027-04-04 |
| Week 14 | 5 April 2027 | 11 April 2027 | 2027-04-05 to 2027-04-11 |
| Week 15 | 12 April 2027 | 18 April 2027 | 2027-04-12 to 2027-04-18 |
| Week 16 | 19 April 2027 | 25 April 2027 | 2027-04-19 to 2027-04-25 |
| Week 17 | 26 April 2027 | 2 May 2027 | 2027-04-26 to 2027-05-02 |
| Week 18 | 3 May 2027 | 9 May 2027 | 2027-05-03 to 2027-05-09 |
| Week 19 | 10 May 2027 | 16 May 2027 | 2027-05-10 to 2027-05-16 |
| Week 20 | 17 May 2027 | 23 May 2027 | 2027-05-17 to 2027-05-23 |
| Week 21 | 24 May 2027 | 30 May 2027 | 2027-05-24 to 2027-05-30 |
| Week 22 | 31 May 2027 | 6 June 2027 | 2027-05-31 to 2027-06-06 |
| Week 23 | 7 June 2027 | 13 June 2027 | 2027-06-07 to 2027-06-13 |
| Week 24 | 14 June 2027 | 20 June 2027 | 2027-06-14 to 2027-06-20 |
| Week 25 | 21 June 2027 | 27 June 2027 | 2027-06-21 to 2027-06-27 |
| Week 26 | 28 June 2027 | 4 July 2027 | 2027-06-28 to 2027-07-04 |
| Week 27 | 5 July 2027 | 11 July 2027 | 2027-07-05 to 2027-07-11 |
| Week 28 | 12 July 2027 | 18 July 2027 | 2027-07-12 to 2027-07-18 |
| Week 29 | 19 July 2027 | 25 July 2027 | 2027-07-19 to 2027-07-25 |
| Week 30 | 26 July 2027 | 1 August 2027 | 2027-07-26 to 2027-08-01 |
| Week 31 | 2 August 2027 | 8 August 2027 | 2027-08-02 to 2027-08-08 |
| Week 32 | 9 August 2027 | 15 August 2027 | 2027-08-09 to 2027-08-15 |
| Week 33 | 16 August 2027 | 22 August 2027 | 2027-08-16 to 2027-08-22 |
| Week 34 | 23 August 2027 | 29 August 2027 | 2027-08-23 to 2027-08-29 |
| Week 35 | 30 August 2027 | 5 September 2027 | 2027-08-30 to 2027-09-05 |
| Week 36 | 6 September 2027 | 12 September 2027 | 2027-09-06 to 2027-09-12 |
| Week 37 | 13 September 2027 | 19 September 2027 | 2027-09-13 to 2027-09-19 |
| Week 38 | 20 September 2027 | 26 September 2027 | 2027-09-20 to 2027-09-26 |
| Week 39 | 27 September 2027 | 3 October 2027 | 2027-09-27 to 2027-10-03 |
| Week 40 | 4 October 2027 | 10 October 2027 | 2027-10-04 to 2027-10-10 |
| Week 41 | 11 October 2027 | 17 October 2027 | 2027-10-11 to 2027-10-17 |
| Week 42 | 18 October 2027 | 24 October 2027 | 2027-10-18 to 2027-10-24 |
| Week 43 | 25 October 2027 | 31 October 2027 | 2027-10-25 to 2027-10-31 |
| Week 44 | 1 November 2027 | 7 November 2027 | 2027-11-01 to 2027-11-07 |
| Week 45 | 8 November 2027 | 14 November 2027 | 2027-11-08 to 2027-11-14 |
| Week 46 | 15 November 2027 | 21 November 2027 | 2027-11-15 to 2027-11-21 |
| Week 47 | 22 November 2027 | 28 November 2027 | 2027-11-22 to 2027-11-28 |
| Week 48 | 29 November 2027 | 5 December 2027 | 2027-11-29 to 2027-12-05 |
| Week 49 | 6 December 2027 | 12 December 2027 | 2027-12-06 to 2027-12-12 |
| Week 50 | 13 December 2027 | 19 December 2027 | 2027-12-13 to 2027-12-19 |
| Week 51 | 20 December 2027 | 26 December 2027 | 2027-12-20 to 2027-12-26 |
| Week 52 | 27 December 2027 | 2 January 2028 | 2027-12-27 to 2028-01-02 |
2027 at a glance
| ISO 8601 weeks | 52 |
|---|---|
| US weeks | 53 |
| Days in the year | 365 |
| Leap year | No |
| 1 January falls on | Friday |
| 31 December falls on | Friday |
Why the first week can start in December
Week 1 of 2027 starts on Monday 4 January 2027. If that date is in December it is not a mistake. ISO 8601 assigns a whole week to the year holding most of its days, so a week straddling New Year belongs to one year or the other rather than being split in half.
The same rule at the other end means the last days of 2027 can fall in week 1 of 2028. Both are correct, and both are shown by the tool above when you enter a date near the boundary.
Frequently asked questions
How many weeks are in 2027?
52 under ISO 8601 numbering, and 53 under the US convention. 2027 is a common year of 365 days, which is 52 weeks and one day over.
When does week 1 of 2027 start?
Monday 4 January 2027 under ISO 8601, which runs Monday to Sunday. Under the US convention it starts on Sunday 27 December 2026. Both can begin in the previous December, which is normal.
Does 2027 have 53 weeks?
No. 2027 has 52 ISO weeks. A year only has 53 when it starts on a Thursday, or on a Wednesday in a leap year, and 1 January 2027 is a Friday.