2027 has 52 ISO weeks. Week 1 starts on Monday, January 4, 2027, because that's the week containing the first Thursday of the year. January 1–3, 2027 (Friday to Sunday) still belong to week 53 of 2026. That's a quirk of the ISO 8601 standard that trips up a lot of spreadsheets.
Who uses week numbers?
Businesses across Europe, especially in Germany, Sweden and the Netherlands, plan everything in week numbers: 'see you in KW 12.' Retailers, factories and software teams use them too, because a week number is shorter and less ambiguous than a date range.
2027 week number table
| Week | Monday | Sunday |
|---|---|---|
| 1 | Jan 4 | Jan 10 |
| 2 | Jan 11 | Jan 17 |
| 3 | Jan 18 | Jan 24 |
| 4 | Jan 25 | Jan 31 |
| 5 | Feb 1 | Feb 7 |
| 6 | Feb 8 | Feb 14 |
| 7 | Feb 15 | Feb 21 |
| 8 | Feb 22 | Feb 28 |
| 9 | Mar 1 | Mar 7 |
| 10 | Mar 8 | Mar 14 |
| 11 | Mar 15 | Mar 21 |
| 12 | Mar 22 | Mar 28 |
| 13 | Mar 29 | Apr 4 |
| 14 | Apr 5 | Apr 11 |
| 15 | Apr 12 | Apr 18 |
| 16 | Apr 19 | Apr 25 |
| 17 | Apr 26 | May 2 |
| 18 | May 3 | May 9 |
| 19 | May 10 | May 16 |
| 20 | May 17 | May 23 |
| 21 | May 24 | May 30 |
| 22 | May 31 | Jun 6 |
| 23 | Jun 7 | Jun 13 |
| 24 | Jun 14 | Jun 20 |
| 25 | Jun 21 | Jun 27 |
| 26 | Jun 28 | Jul 4 |
| 27 | Jul 5 | Jul 11 |
| 28 | Jul 12 | Jul 18 |
| 29 | Jul 19 | Jul 25 |
| 30 | Jul 26 | Aug 1 |
| 31 | Aug 2 | Aug 8 |
| 32 | Aug 9 | Aug 15 |
| 33 | Aug 16 | Aug 22 |
| 34 | Aug 23 | Aug 29 |
| 35 | Aug 30 | Sep 5 |
| 36 | Sep 6 | Sep 12 |
| 37 | Sep 13 | Sep 19 |
| 38 | Sep 20 | Sep 26 |
| 39 | Sep 27 | Oct 3 |
| 40 | Oct 4 | Oct 10 |
| 41 | Oct 11 | Oct 17 |
| 42 | Oct 18 | Oct 24 |
| 43 | Oct 25 | Oct 31 |
| 44 | Nov 1 | Nov 7 |
| 45 | Nov 8 | Nov 14 |
| 46 | Nov 15 | Nov 21 |
| 47 | Nov 22 | Nov 28 |
| 48 | Nov 29 | Dec 5 |
| 49 | Dec 6 | Dec 12 |
| 50 | Dec 13 | Dec 19 |
| 51 | Dec 20 | Dec 26 |
| 52 | Dec 27 | Jan 2 |
Spreadsheet tips
In Excel and Google Sheets, use ISOWEEKNUM(date) rather than WEEKNUM, which uses a different system by default. In the US, some calendars start weeks on Sunday and call the week containing January 1 'week 1,' which gives different numbers. Always say which system you mean when sharing a plan.
Want today's week number? See what day is today, or read how many weeks are in a year.