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Week Numbers 1991
| Week # | Start date (Mon) | End date (Sun) |
|---|---|---|
| ▸ 1 | Mon, 31 Dec 1990 | Sun, 6 Jan 1991 |
| ▸ 2 | Mon, 7 Jan 1991 | Sun, 13 Jan 1991 |
| ▸ 3 | Mon, 14 Jan 1991 | Sun, 20 Jan 1991 |
| ▸ 4 | Mon, 21 Jan 1991 | Sun, 27 Jan 1991 |
| ▸ 5 | Mon, 28 Jan 1991 | Sun, 3 Feb 1991 |
| ▸ 6 | Mon, 4 Feb 1991 | Sun, 10 Feb 1991 |
| ▸ 7 | Mon, 11 Feb 1991 | Sun, 17 Feb 1991 |
| ▸ 8 | Mon, 18 Feb 1991 | Sun, 24 Feb 1991 |
| ▸ 9 | Mon, 25 Feb 1991 | Sun, 3 Mar 1991 |
| ▸ 10 | Mon, 4 Mar 1991 | Sun, 10 Mar 1991 |
| ▸ 11 | Mon, 11 Mar 1991 | Sun, 17 Mar 1991 |
| ▸ 12 | Mon, 18 Mar 1991 | Sun, 24 Mar 1991 |
| ▸ 13 | Mon, 25 Mar 1991 | Sun, 31 Mar 1991 |
| ▸ 14 | Mon, 1 Apr 1991 | Sun, 7 Apr 1991 |
| ▸ 15 | Mon, 8 Apr 1991 | Sun, 14 Apr 1991 |
| ▸ 16 | Mon, 15 Apr 1991 | Sun, 21 Apr 1991 |
| ▸ 17 | Mon, 22 Apr 1991 | Sun, 28 Apr 1991 |
| ▸ 18 | Mon, 29 Apr 1991 | Sun, 5 May 1991 |
| ▸ 19 | Mon, 6 May 1991 | Sun, 12 May 1991 |
| ▸ 20 | Mon, 13 May 1991 | Sun, 19 May 1991 |
| ▸ 21 | Mon, 20 May 1991 | Sun, 26 May 1991 |
| ▸ 22 | Mon, 27 May 1991 | Sun, 2 Jun 1991 |
| ▸ 23 | Mon, 3 Jun 1991 | Sun, 9 Jun 1991 |
| ▸ 24 | Mon, 10 Jun 1991 | Sun, 16 Jun 1991 |
| ▸ 25 | Mon, 17 Jun 1991 | Sun, 23 Jun 1991 |
| ▸ 26 | Mon, 24 Jun 1991 | Sun, 30 Jun 1991 |
| ▸ 27 | Mon, 1 Jul 1991 | Sun, 7 Jul 1991 |
| ▸ 28 | Mon, 8 Jul 1991 | Sun, 14 Jul 1991 |
| ▸ 29 | Mon, 15 Jul 1991 | Sun, 21 Jul 1991 |
| ▸ 30 | Mon, 22 Jul 1991 | Sun, 28 Jul 1991 |
| ▸ 31 | Mon, 29 Jul 1991 | Sun, 4 Aug 1991 |
| ▸ 32 | Mon, 5 Aug 1991 | Sun, 11 Aug 1991 |
| ▸ 33 | Mon, 12 Aug 1991 | Sun, 18 Aug 1991 |
| ▸ 34 | Mon, 19 Aug 1991 | Sun, 25 Aug 1991 |
| ▸ 35 | Mon, 26 Aug 1991 | Sun, 1 Sep 1991 |
| ▸ 36 | Mon, 2 Sep 1991 | Sun, 8 Sep 1991 |
| ▸ 37 | Mon, 9 Sep 1991 | Sun, 15 Sep 1991 |
| ▸ 38 | Mon, 16 Sep 1991 | Sun, 22 Sep 1991 |
| ▸ 39 | Mon, 23 Sep 1991 | Sun, 29 Sep 1991 |
| ▸ 40 | Mon, 30 Sep 1991 | Sun, 6 Oct 1991 |
| ▸ 41 | Mon, 7 Oct 1991 | Sun, 13 Oct 1991 |
| ▸ 42 | Mon, 14 Oct 1991 | Sun, 20 Oct 1991 |
| ▸ 43 | Mon, 21 Oct 1991 | Sun, 27 Oct 1991 |
| ▸ 44 | Mon, 28 Oct 1991 | Sun, 3 Nov 1991 |
| ▸ 45 | Mon, 4 Nov 1991 | Sun, 10 Nov 1991 |
| ▸ 46 | Mon, 11 Nov 1991 | Sun, 17 Nov 1991 |
| ▸ 47 | Mon, 18 Nov 1991 | Sun, 24 Nov 1991 |
| ▸ 48 | Mon, 25 Nov 1991 | Sun, 1 Dec 1991 |
| ▸ 49 | Mon, 2 Dec 1991 | Sun, 8 Dec 1991 |
| ▸ 50 | Mon, 9 Dec 1991 | Sun, 15 Dec 1991 |
| ▸ 51 | Mon, 16 Dec 1991 | Sun, 22 Dec 1991 |
| ▸ 52 | Mon, 23 Dec 1991 | Sun, 29 Dec 1991 |
About ISO 8601 Week Numbers
Under the ISO 8601 standard, weeks start on Monday and are numbered from 1 to 52 or 53. Week 1 is the week that contains the first Thursday of the year — equivalently, the week containing January 4th. As a result, the first few days of January can fall in the last week of the previous year, and the last days of December can fall in week 1 of the next year.
A year has 53 ISO weeks when it starts on a Thursday, or on a Wednesday in a leap year; otherwise it has 52. 1991 has 52 ISO weeks.