What Week Is It?
See what week it is today: the box at the top shows the ISO 8601 week number for today’s date on your device, in your time zone, with the Monday and Sunday of the week. Pick any date to get its ISO week, its week-year (1 January 2027, for example, is still in week 53 of 2026) and the dates of that week. Below it is the full table of ISO week numbers for 2027, from week 1 (Monday 4 January) to week 52 (ending Sunday 2 January 2028), or for any year from 2026 to 2030; download it as a PDF on US Letter or A4, or as a CSV for a spreadsheet. ISO weeks run Monday to Sunday and week 1 is the week with the year’s first Thursday. If you need US-style numbering instead (Sunday start, week 1 contains 1 January), switch the system: it is labelled, because the numbers can differ by one.
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This week (ISO 8601)
Week
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Week table
Everything runs in your browser: the week numbers are calculated on your device from your clock and time zone, and only the year, system and paper you pick are remembered in this browser. ISO 8601 weeks run Monday to Sunday and week 1 is the week with the year’s first Thursday; US-style numbering (Sunday start, week 1 contains 1 January) is a different system and is labelled wherever it is shown. PDF export uses jsPDF and svg2pdf.js (MIT licence); print at 100% (actual size).
How to find a week number
- Read today’s week number in the box at the top.
- Pick a date to see its ISO week, week-year and Monday to Sunday dates.
- Choose a year from 2026 to 2030 for the full week table.
- Switch to US style only if your workplace numbers weeks from Sunday with week 1 containing 1 January.
- Download the table as a PDF (US Letter or A4) or a CSV.
What you can use it for
- Quoting week numbers in project plans, sprints and timesheets
- Payroll, shipping and production schedules that run on ISO weeks
- Booking school or office weeks in Europe, where ISO weeks are standard
- A printed week-number sheet next to the 2027 calendar
- Checking which week-year a date at the turn of the year belongs to
ISO week numbers 2027
| Week | Monday | Sunday |
|---|---|---|
| W01 | Jan 4, 2027 | Jan 10, 2027 |
| W02 | Jan 11, 2027 | Jan 17, 2027 |
| W03 | Jan 18, 2027 | Jan 24, 2027 |
| W04 | Jan 25, 2027 | Jan 31, 2027 |
| W05 | Feb 1, 2027 | Feb 7, 2027 |
| W06 | Feb 8, 2027 | Feb 14, 2027 |
| W07 | Feb 15, 2027 | Feb 21, 2027 |
| W08 | Feb 22, 2027 | Feb 28, 2027 |
| W09 | Mar 1, 2027 | Mar 7, 2027 |
| W10 | Mar 8, 2027 | Mar 14, 2027 |
| W11 | Mar 15, 2027 | Mar 21, 2027 |
| W12 | Mar 22, 2027 | Mar 28, 2027 |
| W13 | Mar 29, 2027 | Apr 4, 2027 |
| W14 | Apr 5, 2027 | Apr 11, 2027 |
| W15 | Apr 12, 2027 | Apr 18, 2027 |
| W16 | Apr 19, 2027 | Apr 25, 2027 |
| W17 | Apr 26, 2027 | May 2, 2027 |
| W18 | May 3, 2027 | May 9, 2027 |
| W19 | May 10, 2027 | May 16, 2027 |
| W20 | May 17, 2027 | May 23, 2027 |
| W21 | May 24, 2027 | May 30, 2027 |
| W22 | May 31, 2027 | Jun 6, 2027 |
| W23 | Jun 7, 2027 | Jun 13, 2027 |
| W24 | Jun 14, 2027 | Jun 20, 2027 |
| W25 | Jun 21, 2027 | Jun 27, 2027 |
| W26 | Jun 28, 2027 | Jul 4, 2027 |
| W27 | Jul 5, 2027 | Jul 11, 2027 |
| W28 | Jul 12, 2027 | Jul 18, 2027 |
| W29 | Jul 19, 2027 | Jul 25, 2027 |
| W30 | Jul 26, 2027 | Aug 1, 2027 |
| W31 | Aug 2, 2027 | Aug 8, 2027 |
| W32 | Aug 9, 2027 | Aug 15, 2027 |
| W33 | Aug 16, 2027 | Aug 22, 2027 |
| W34 | Aug 23, 2027 | Aug 29, 2027 |
| W35 | Aug 30, 2027 | Sep 5, 2027 |
| W36 | Sep 6, 2027 | Sep 12, 2027 |
| W37 | Sep 13, 2027 | Sep 19, 2027 |
| W38 | Sep 20, 2027 | Sep 26, 2027 |
| W39 | Sep 27, 2027 | Oct 3, 2027 |
| W40 | Oct 4, 2027 | Oct 10, 2027 |
| W41 | Oct 11, 2027 | Oct 17, 2027 |
| W42 | Oct 18, 2027 | Oct 24, 2027 |
| W43 | Oct 25, 2027 | Oct 31, 2027 |
| W44 | Nov 1, 2027 | Nov 7, 2027 |
| W45 | Nov 8, 2027 | Nov 14, 2027 |
| W46 | Nov 15, 2027 | Nov 21, 2027 |
| W47 | Nov 22, 2027 | Nov 28, 2027 |
| W48 | Nov 29, 2027 | Dec 5, 2027 |
| W49 | Dec 6, 2027 | Dec 12, 2027 |
| W50 | Dec 13, 2027 | Dec 19, 2027 |
| W51 | Dec 20, 2027 | Dec 26, 2027 |
| W52 | Dec 27, 2027 | Jan 2, 2028 |
2027 has 52 ISO weeks. 1–3 January 2027 belong to week 53 of 2026; 1–2 January 2028 belong to week 52 of 2027.
Years with 53 ISO weeks
| Year | ISO weeks | Week 1 starts | Last week ends |
|---|---|---|---|
| 2026 | 53 | Dec 29, 2025 | Jan 3, 2027 |
| 2027 | 52 | Jan 4, 2027 | Jan 2, 2028 |
| 2028 | 52 | Jan 3, 2028 | Dec 31, 2028 |
| 2029 | 52 | Jan 1, 2029 | Dec 30, 2029 |
| 2030 | 52 | Dec 31, 2029 | Dec 29, 2030 |
A year has 53 ISO weeks when it starts on a Thursday, or is a leap year that starts on a Wednesday. Between 2000 and 2040: 2004, 2009, 2015, 2020, 2026, 2032 and 2037.
How ISO week numbers work
ISO 8601 numbers weeks from Monday to Sunday. Week 1 of a year is the first week that contains a Thursday, so it always contains 4 January, and a week belongs to the year that holds its Thursday. Source: the ISO calendar as described for date.isocalendar() in the Python datetime documentation (read 13 November 2026); every date in the tool and on this page is checked against it.
US-style week numbers are a different system: weeks run Sunday to Saturday and week 1 is the week that contains 1 January. The tool offers them as an option and labels them.
More for planning by the week
- A dated page for every week of 2027: 2027 Weekly Planner.
- The year on one page: 2027 Calendar.
- Any month of any year: Calendar Maker.
More free calendars and planners
Planning ahead?
Calendars, planners and trackers you can print at home: free, private, no sign-up.
See all free tools →Frequently asked questions
What week is it today?
The box at the top of this page shows it: today’s ISO week number, calculated from your device’s date in your time zone, with the Monday and Sunday of the week. It updates when the date changes.
How many weeks are in 2027?
52 ISO weeks. Week 1 starts on Monday 4 January 2027 and week 52 ends on Sunday 2 January 2028.
What week is 1 January 2027?
Week 53 of 2026. 1 January 2027 is a Friday, so that week’s Thursday falls in 2026; ISO week 1 of 2027 starts on Monday 4 January.
Does 2026 have 53 weeks?
Yes. 2026 starts on a Thursday, so it has 53 ISO weeks; week 53 runs from Monday 28 December 2026 to Sunday 3 January 2027. Between 2000 and 2040 the years with 53 ISO weeks are 2004, 2009, 2015, 2020, 2026, 2032 and 2037.
How are ISO week numbers worked out?
ISO 8601 weeks start on Monday and end on Sunday. Week 1 is the week that contains the year’s first Thursday, which is also the week that contains 4 January. A date near New Year can therefore belong to the previous or the next week-year.
What is the difference between ISO and US week numbers?
US-style numbering starts weeks on Sunday and calls the week that contains 1 January week 1, even if it is mostly in December. For 2027 that gives 53 US weeks, the first starting Sunday 27 December 2026, while ISO gives 52. The tool labels whichever system you pick.
Which week is 31 December 2029?
Week 1 of 2030 (2030-W01): 31 December 2029 is a Monday, and that week’s Thursday is 3 January 2030.
Can I print the week numbers?
Yes. Download the table for any year from 2026 to 2030 as a one-page PDF on US Letter or A4, or as a CSV with the week, its Monday and its Sunday.
Is my information uploaded?
No. Your dates and settings stay in this browser, and the PDF and images are made on your device.