Week numbers 2027: calendar weeks with dates
Week numbers 2027: every ISO calendar week of 2027 with its Monday and Sunday dates. 2027 has the usual 52 weeks, and because 1 January 2027 is a Friday, the year's first three days still count as week 53 of 2026.
With JavaScript on, this line names the week that contains today and marks it in the table.
Every week of 2027
ISO weeks run from Monday to Sunday. Week 1 of 2027 starts on Monday 4 January 2027 and week 52 ends on Sunday 2 January 2028. Dates outside 2027 show their year.
| Week | Monday | Sunday | Months |
|---|---|---|---|
| 1 | Mon 4 January | Sun 10 January | January |
| 2 | Mon 11 January | Sun 17 January | January |
| 3 | Mon 18 January | Sun 24 January | January |
| 4 | Mon 25 January | Sun 31 January | January |
| 5 | Mon 1 February | Sun 7 February | February |
| 6 | Mon 8 February | Sun 14 February | February |
| 7 | Mon 15 February | Sun 21 February | February |
| 8 | Mon 22 February | Sun 28 February | February |
| 9 | Mon 1 March | Sun 7 March | March |
| 10 | Mon 8 March | Sun 14 March | March |
| 11 | Mon 15 March | Sun 21 March | March |
| 12 | Mon 22 March | Sun 28 March | March |
| 13 | Mon 29 March | Sun 4 April | March and April |
| 14 | Mon 5 April | Sun 11 April | April |
| 15 | Mon 12 April | Sun 18 April | April |
| 16 | Mon 19 April | Sun 25 April | April |
| 17 | Mon 26 April | Sun 2 May | April and May |
| 18 | Mon 3 May | Sun 9 May | May |
| 19 | Mon 10 May | Sun 16 May | May |
| 20 | Mon 17 May | Sun 23 May | May |
| 21 | Mon 24 May | Sun 30 May | May |
| 22 | Mon 31 May | Sun 6 June | May and June |
| 23 | Mon 7 June | Sun 13 June | June |
| 24 | Mon 14 June | Sun 20 June | June |
| 25 | Mon 21 June | Sun 27 June | June |
| 26 | Mon 28 June | Sun 4 July | June and July |
| 27 | Mon 5 July | Sun 11 July | July |
| 28 | Mon 12 July | Sun 18 July | July |
| 29 | Mon 19 July | Sun 25 July | July |
| 30 | Mon 26 July | Sun 1 August | July and August |
| 31 | Mon 2 August | Sun 8 August | August |
| 32 | Mon 9 August | Sun 15 August | August |
| 33 | Mon 16 August | Sun 22 August | August |
| 34 | Mon 23 August | Sun 29 August | August |
| 35 | Mon 30 August | Sun 5 September | August and September |
| 36 | Mon 6 September | Sun 12 September | September |
| 37 | Mon 13 September | Sun 19 September | September |
| 38 | Mon 20 September | Sun 26 September | September |
| 39 | Mon 27 September | Sun 3 October | September and October |
| 40 | Mon 4 October | Sun 10 October | October |
| 41 | Mon 11 October | Sun 17 October | October |
| 42 | Mon 18 October | Sun 24 October | October |
| 43 | Mon 25 October | Sun 31 October | October |
| 44 | Mon 1 November | Sun 7 November | November |
| 45 | Mon 8 November | Sun 14 November | November |
| 46 | Mon 15 November | Sun 21 November | November |
| 47 | Mon 22 November | Sun 28 November | November |
| 48 | Mon 29 November | Sun 5 December | November and December |
| 49 | Mon 6 December | Sun 12 December | December |
| 50 | Mon 13 December | Sun 19 December | December |
| 51 | Mon 20 December | Sun 26 December | December |
| 52 | Mon 27 December | Sun 2 January 2028 | December and January |
Need the week for one date, or a date outside 2027? The week number calculator gives the ISO week, the US week and the day of the year for any date, and the dates of any week.
Why 2027 has 52 weeks
2027 has 52 numbered weeks, which is the normal case. A year only gets a 53rd week when it starts on a Thursday, or on a Wednesday in a leap year, and 2027 starts on a Friday. That Friday matters in another way: under the ISO rule a week belongs to the year that holds its Thursday, and the Thursday of the week containing 1 January 2027 is 31 December 2026. So Friday 1, Saturday 2 and Sunday 3 January 2027 are the tail of 2026's week 53, and week 1 of 2027 does not start until Monday 4 January 2027.
The same thing happens at the other end. Week 52 starts on Monday 27 December 2027 and ends on Sunday 2 January 2028, so the first two days of 2028 are counted as 2027 week 52. Anyone filing a report for "week 1" at the start of January 2027 should check which year's week 1 they mean.
ISO weeks and US (Sunday start) weeks in 2027
A calendar that starts its weeks on Sunday, as most US calendars and Excel's WEEKNUM do by default, numbers 2027 differently. Its week 1 is Sunday 27 December 2026 to Saturday 2 January 2027, the week with 1 January in it, and it has 53 numbered weeks, ending with a week 53 that is 26 to 31 December. From 4 January onwards the ISO numbers in the table run one behind the Sunday-start numbers, except on Sundays, when they are two behind. Use the week number calculator to see both numbers for a date.
Weeks that cross a month boundary
9 of the 52 weeks of 2027 begin in one month and end in the next. If your team reports by week and by month, decide once which month such a week belongs to: the month of its Monday, the month with four or more of its days, or the month of its Thursday. The straddling weeks in 2027 are numbers 13, 17, 22, 26, 30, 35, 39, 48, 52.
See also week numbers for 2026 and 2027, or go straight to week numbers 2026. For deadlines in working days, the business days calculator skips weekends and your own holidays.
Questions people ask
How many weeks are in 2027?
2027 has 52 ISO weeks. 1 January 2027 falls on a Friday, so the year does not qualify for a 53rd week; that only happens when a year starts on a Thursday, or on a Wednesday in a leap year.
What week is 1 January 2027?
Under ISO 8601, 1 January 2027 is in week 53 of 2026, because the week it sits in (28 December 2026 to 3 January 2027) has its Thursday in December 2026. Week 1 of 2027 begins on Monday 4 January 2027. Under the US (Sunday start) rule, 1 January 2027 is week 1.
Which is the last week of 2027?
Week 52, from Monday 27 December 2027 to Sunday 2 January 2028. It includes 1 and 2 January 2028, which belong to 2027's week 52 rather than to 2028.
How many weeks in 2027 cross from one month into the next?
9 weeks: numbers 13, 17, 22, 26, 30, 35, 39, 48, 52. Week 1 (4 January to 10 January 2027) sits entirely inside January, while week 52 runs from December 2027 into January 2028.