Week numbers 2027
All 52 ISO weeks of 2027 with their date ranges, alongside the US numbering for the same weeks. Under ISO 8601, week 1 of 2027 begins on 4 Jan 2027.
| Week | ISO 8601 (Monday start) | US (Sunday start) |
|---|---|---|
| 1 | 4 Jan to 10 Jan | 27 Dec to 2 Jan |
| 2 | 11 Jan to 17 Jan | 3 Jan to 9 Jan |
| 3 | 18 Jan to 24 Jan | 10 Jan to 16 Jan |
| 4 | 25 Jan to 31 Jan | 17 Jan to 23 Jan |
| 5 | 1 Feb to 7 Feb | 24 Jan to 30 Jan |
| 6 | 8 Feb to 14 Feb | 31 Jan to 6 Feb |
| 7 | 15 Feb to 21 Feb | 7 Feb to 13 Feb |
| 8 | 22 Feb to 28 Feb | 14 Feb to 20 Feb |
| 9 | 1 Mar to 7 Mar | 21 Feb to 27 Feb |
| 10 | 8 Mar to 14 Mar | 28 Feb to 6 Mar |
| 11 | 15 Mar to 21 Mar | 7 Mar to 13 Mar |
| 12 | 22 Mar to 28 Mar | 14 Mar to 20 Mar |
| 13 | 29 Mar to 4 Apr | 21 Mar to 27 Mar |
| 14 | 5 Apr to 11 Apr | 28 Mar to 3 Apr |
| 15 | 12 Apr to 18 Apr | 4 Apr to 10 Apr |
| 16 | 19 Apr to 25 Apr | 11 Apr to 17 Apr |
| 17 | 26 Apr to 2 May | 18 Apr to 24 Apr |
| 18 | 3 May to 9 May | 25 Apr to 1 May |
| 19 | 10 May to 16 May | 2 May to 8 May |
| 20 | 17 May to 23 May | 9 May to 15 May |
| 21 | 24 May to 30 May | 16 May to 22 May |
| 22 | 31 May to 6 Jun | 23 May to 29 May |
| 23 | 7 Jun to 13 Jun | 30 May to 5 Jun |
| 24 | 14 Jun to 20 Jun | 6 Jun to 12 Jun |
| 25 | 21 Jun to 27 Jun | 13 Jun to 19 Jun |
| 26 | 28 Jun to 4 Jul | 20 Jun to 26 Jun |
| 27 | 5 Jul to 11 Jul | 27 Jun to 3 Jul |
| 28 | 12 Jul to 18 Jul | 4 Jul to 10 Jul |
| 29 | 19 Jul to 25 Jul | 11 Jul to 17 Jul |
| 30 | 26 Jul to 1 Aug | 18 Jul to 24 Jul |
| 31 | 2 Aug to 8 Aug | 25 Jul to 31 Jul |
| 32 | 9 Aug to 15 Aug | 1 Aug to 7 Aug |
| 33 | 16 Aug to 22 Aug | 8 Aug to 14 Aug |
| 34 | 23 Aug to 29 Aug | 15 Aug to 21 Aug |
| 35 | 30 Aug to 5 Sep | 22 Aug to 28 Aug |
| 36 | 6 Sep to 12 Sep | 29 Aug to 4 Sep |
| 37 | 13 Sep to 19 Sep | 5 Sep to 11 Sep |
| 38 | 20 Sep to 26 Sep | 12 Sep to 18 Sep |
| 39 | 27 Sep to 3 Oct | 19 Sep to 25 Sep |
| 40 | 4 Oct to 10 Oct | 26 Sep to 2 Oct |
| 41 | 11 Oct to 17 Oct | 3 Oct to 9 Oct |
| 42 | 18 Oct to 24 Oct | 10 Oct to 16 Oct |
| 43 | 25 Oct to 31 Oct | 17 Oct to 23 Oct |
| 44 | 1 Nov to 7 Nov | 24 Oct to 30 Oct |
| 45 | 8 Nov to 14 Nov | 31 Oct to 6 Nov |
| 46 | 15 Nov to 21 Nov | 7 Nov to 13 Nov |
| 47 | 22 Nov to 28 Nov | 14 Nov to 20 Nov |
| 48 | 29 Nov to 5 Dec | 21 Nov to 27 Nov |
| 49 | 6 Dec to 12 Dec | 28 Nov to 4 Dec |
| 50 | 13 Dec to 19 Dec | 5 Dec to 11 Dec |
| 51 | 20 Dec to 26 Dec | 12 Dec to 18 Dec |
| 52 | 27 Dec to 2 Jan | 19 Dec to 25 Dec |
See it on a calendar. Open the week calendar for three years of week rows side by side, with your own leave, travel and deadlines marked on them. Free, no sign-up.
Why two systems disagree
Everyone agrees a year has weeks. Nobody agrees which one is week 1, and that is where the two numbers come from.
ISO 8601, used across Europe and by most software, starts weeks on Monday and gives week 1 to the first week with four or more of its days in the new year. That is usually described as "the week containing the first Thursday", which is the same rule said differently: Thursday is the fourth day of a Monday-start week.
The US convention starts weeks on Sunday and gives week 1 to whatever week holds 1 January. It is easier to explain and it produces a 53rd week far more often.
The two can differ by a full week for the same date, which is exactly the sort of thing that goes unnoticed until two reports disagree at a year end.
Other years: 2024 · 2025 · 2026 · 2028 · 2029 · what week is it now