| Week 1 | January 2 – January 8, 2012 |
| Week 2 | January 9 – January 15, 2012 |
| Week 3 | January 16 – January 22, 2012 |
| Week 4 | January 23 – January 29, 2012 |
| Week 5 | January 30 – February 5, 2012 |
| Week 6 | February 6 – February 12, 2012 |
| Week 7 | February 13 – February 19, 2012 |
| Week 8 | February 20 – February 26, 2012 |
| Week 9 | February 27 – March 4, 2012 |
| Week 10 | March 5 – March 11, 2012 |
| Week 11 | March 12 – March 18, 2012 |
| Week 12 | March 19 – March 25, 2012 |
| Week 13 | March 26 – April 1, 2012 |
| Week 14 | April 2 – April 8, 2012 |
| Week 15 | April 9 – April 15, 2012 |
| Week 16 | April 16 – April 22, 2012 |
| Week 17 | April 23 – April 29, 2012 |
| Week 18 | April 30 – May 6, 2012 |
| Week 19 | May 7 – May 13, 2012 |
| Week 20 | May 14 – May 20, 2012 |
| Week 21 | May 21 – May 27, 2012 |
| Week 22 | May 28 – June 3, 2012 |
| Week 23 | June 4 – June 10, 2012 |
| Week 24 | June 11 – June 17, 2012 |
| Week 25 | June 18 – June 24, 2012 |
| Week 26 | June 25 – July 1, 2012 |
| Week 27 | July 2 – July 8, 2012 |
| Week 28 | July 9 – July 15, 2012 |
| Week 29 | July 16 – July 22, 2012 |
| Week 30 | July 23 – July 29, 2012 |
| Week 31 | July 30 – August 5, 2012 |
| Week 32 | August 6 – August 12, 2012 |
| Week 33 | August 13 – August 19, 2012 |
| Week 34 | August 20 – August 26, 2012 |
| Week 35 | August 27 – September 2, 2012 |
| Week 36 | September 3 – September 9, 2012 |
| Week 37 | September 10 – September 16, 2012 |
| Week 38 | September 17 – September 23, 2012 |
| Week 39 | September 24 – September 30, 2012 |
| Week 40 | October 1 – October 7, 2012 |
| Week 41 | October 8 – October 14, 2012 |
| Week 42 | October 15 – October 21, 2012 |
| Week 43 | October 22 – October 28, 2012 |
| Week 44 | October 29 – November 4, 2012 |
| Week 45 | November 5 – November 11, 2012 |
| Week 46 | November 12 – November 18, 2012 |
| Week 47 | November 19 – November 25, 2012 |
| Week 48 | November 26 – December 2, 2012 |
| Week 49 | December 3 – December 9, 2012 |
| Week 50 | December 10 – December 16, 2012 |
| Week 51 | December 17 – December 23, 2012 |
| Week 52 | December 24 – December 30, 2012 |
2012 has 52 ISO weeks. Most years have 52; a year has 53 when it starts on a Thursday (or on a Wednesday in a leap year).
Week 1 of 2012 starts on Monday, January 2, 2012 — ISO week 1 is the week containing the year's first Thursday, so it can start in late December.
=ISOWEEKNUM(A1) returns the ISO week number of the date in A1 (the numbering used on this page); =WEEKNUM(A1) uses the US Sunday-start convention. Both work in Excel and Google Sheets.