| Week 1 | December 31, 2018 – January 6, 2019 |
| Week 2 | January 7 – January 13, 2019 |
| Week 3 | January 14 – January 20, 2019 |
| Week 4 | January 21 – January 27, 2019 |
| Week 5 | January 28 – February 3, 2019 |
| Week 6 | February 4 – February 10, 2019 |
| Week 7 | February 11 – February 17, 2019 |
| Week 8 | February 18 – February 24, 2019 |
| Week 9 | February 25 – March 3, 2019 |
| Week 10 | March 4 – March 10, 2019 |
| Week 11 | March 11 – March 17, 2019 |
| Week 12 | March 18 – March 24, 2019 |
| Week 13 | March 25 – March 31, 2019 |
| Week 14 | April 1 – April 7, 2019 |
| Week 15 | April 8 – April 14, 2019 |
| Week 16 | April 15 – April 21, 2019 |
| Week 17 | April 22 – April 28, 2019 |
| Week 18 | April 29 – May 5, 2019 |
| Week 19 | May 6 – May 12, 2019 |
| Week 20 | May 13 – May 19, 2019 |
| Week 21 | May 20 – May 26, 2019 |
| Week 22 | May 27 – June 2, 2019 |
| Week 23 | June 3 – June 9, 2019 |
| Week 24 | June 10 – June 16, 2019 |
| Week 25 | June 17 – June 23, 2019 |
| Week 26 | June 24 – June 30, 2019 |
| Week 27 | July 1 – July 7, 2019 |
| Week 28 | July 8 – July 14, 2019 |
| Week 29 | July 15 – July 21, 2019 |
| Week 30 | July 22 – July 28, 2019 |
| Week 31 | July 29 – August 4, 2019 |
| Week 32 | August 5 – August 11, 2019 |
| Week 33 | August 12 – August 18, 2019 |
| Week 34 | August 19 – August 25, 2019 |
| Week 35 | August 26 – September 1, 2019 |
| Week 36 | September 2 – September 8, 2019 |
| Week 37 | September 9 – September 15, 2019 |
| Week 38 | September 16 – September 22, 2019 |
| Week 39 | September 23 – September 29, 2019 |
| Week 40 | September 30 – October 6, 2019 |
| Week 41 | October 7 – October 13, 2019 |
| Week 42 | October 14 – October 20, 2019 |
| Week 43 | October 21 – October 27, 2019 |
| Week 44 | October 28 – November 3, 2019 |
| Week 45 | November 4 – November 10, 2019 |
| Week 46 | November 11 – November 17, 2019 |
| Week 47 | November 18 – November 24, 2019 |
| Week 48 | November 25 – December 1, 2019 |
| Week 49 | December 2 – December 8, 2019 |
| Week 50 | December 9 – December 15, 2019 |
| Week 51 | December 16 – December 22, 2019 |
| Week 52 | December 23 – December 29, 2019 |
2019 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 2019 starts on Monday, December 31, 2018 — 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.