# Find the week number of any date, in the ISO and US systems. Last updated October 31, 2026FreeNo signupFormula shown Pick a date to see its week number, or type a week number to see its dates. Switch between the ISO system used in most of the world and the US system that Excel starts from, and print every week of the year with its start and end dates. Need the day of the year instead? Try the [Julian date calendar](https://www.teampredict.ai/tools/julian-date-calendar). Date Today Week numbering ISO (Monday start)US (Sunday start) Weeks run Monday to Sunday. Week 1 holds the first Thursday of the year. Find the dates of a week number Week Year Week 44 of 2026: Mon, Oct 26, 2026 to Sun, Nov 1, 2026 ISO week number of Mon, Nov 2, 2026 45of 53 Mon, Nov 2, 2026 to Sun, Nov 8, 2026 teampredict.ai/tools/week-number About this date Weekday Monday US week number Week 45 Day of the year 306 ISO week date 2026-W45-1 Weeks left in the year 8 Days left in the year 59 ‹2026 and 2027› Print the ISO week table Copy resultsCopy link ISO week numbers for 2026 and 2027 Weeks run Monday to Sunday. Week 1 holds the first Thursday of the year. teampredict.ai/tools/week-number ISO weeks of 2026 and 2027 Every ISO week of 2026 and 2027 with its first and last day Week 2026 2027 Monday Sunday Monday Sunday 1 Dec 29, 2025 Jan 4 Jan 4 Jan 10 2 Jan 5 Jan 11 Jan 11 Jan 17 3 Jan 12 Jan 18 Jan 18 Jan 24 4 Jan 19 Jan 25 Jan 25 Jan 31 5 Jan 26 Feb 1 Feb 1 Feb 7 6 Feb 2 Feb 8 Feb 8 Feb 14 7 Feb 9 Feb 15 Feb 15 Feb 21 8 Feb 16 Feb 22 Feb 22 Feb 28 9 Feb 23 Mar 1 Mar 1 Mar 7 10 Mar 2 Mar 8 Mar 8 Mar 14 11 Mar 9 Mar 15 Mar 15 Mar 21 12 Mar 16 Mar 22 Mar 22 Mar 28 13 Mar 23 Mar 29 Mar 29 Apr 4 14 Mar 30 Apr 5 Apr 5 Apr 11 15 Apr 6 Apr 12 Apr 12 Apr 18 16 Apr 13 Apr 19 Apr 19 Apr 25 17 Apr 20 Apr 26 Apr 26 May 2 18 Apr 27 May 3 May 3 May 9 19 May 4 May 10 May 10 May 16 20 May 11 May 17 May 17 May 23 21 May 18 May 24 May 24 May 30 22 May 25 May 31 May 31 Jun 6 23 Jun 1 Jun 7 Jun 7 Jun 13 24 Jun 8 Jun 14 Jun 14 Jun 20 25 Jun 15 Jun 21 Jun 21 Jun 27 26 Jun 22 Jun 28 Jun 28 Jul 4 27 Jun 29 Jul 5 Jul 5 Jul 11 28 Jul 6 Jul 12 Jul 12 Jul 18 29 Jul 13 Jul 19 Jul 19 Jul 25 30 Jul 20 Jul 26 Jul 26 Aug 1 31 Jul 27 Aug 2 Aug 2 Aug 8 32 Aug 3 Aug 9 Aug 9 Aug 15 33 Aug 10 Aug 16 Aug 16 Aug 22 34 Aug 17 Aug 23 Aug 23 Aug 29 35 Aug 24 Aug 30 Aug 30 Sep 5 36 Aug 31 Sep 6 Sep 6 Sep 12 37 Sep 7 Sep 13 Sep 13 Sep 19 38 Sep 14 Sep 20 Sep 20 Sep 26 39 Sep 21 Sep 27 Sep 27 Oct 3 40 Sep 28 Oct 4 Oct 4 Oct 10 41 Oct 5 Oct 11 Oct 11 Oct 17 42 Oct 12 Oct 18 Oct 18 Oct 24 43 Oct 19 Oct 25 Oct 25 Oct 31 44 Oct 26 Nov 1 Nov 1 Nov 7 45 Nov 2 Nov 8 Nov 8 Nov 14 46 Nov 9 Nov 15 Nov 15 Nov 21 47 Nov 16 Nov 22 Nov 22 Nov 28 48 Nov 23 Nov 29 Nov 29 Dec 5 49 Nov 30 Dec 6 Dec 6 Dec 12 50 Dec 7 Dec 13 Dec 13 Dec 19 51 Dec 14 Dec 20 Dec 20 Dec 26 52 Dec 21 Dec 27 Dec 27 Jan 2, 2028 53 Dec 28 Jan 3, 2027 2026 has 53 ISO weeks and 2027 has 52. US week numbers for 2026 and 2027 Weeks run Sunday to Saturday. Week 1 holds January 1. teampredict.ai/tools/week-number US weeks of 2026 and 2027 Every US week of 2026 and 2027 with its first and last day Week 2026 2027 Sunday Saturday Sunday Saturday 1 Dec 28, 2025 Jan 3 Dec 27, 2026 Jan 2 2 Jan 4 Jan 10 Jan 3 Jan 9 3 Jan 11 Jan 17 Jan 10 Jan 16 4 Jan 18 Jan 24 Jan 17 Jan 23 5 Jan 25 Jan 31 Jan 24 Jan 30 6 Feb 1 Feb 7 Jan 31 Feb 6 7 Feb 8 Feb 14 Feb 7 Feb 13 8 Feb 15 Feb 21 Feb 14 Feb 20 9 Feb 22 Feb 28 Feb 21 Feb 27 10 Mar 1 Mar 7 Feb 28 Mar 6 11 Mar 8 Mar 14 Mar 7 Mar 13 12 Mar 15 Mar 21 Mar 14 Mar 20 13 Mar 22 Mar 28 Mar 21 Mar 27 14 Mar 29 Apr 4 Mar 28 Apr 3 15 Apr 5 Apr 11 Apr 4 Apr 10 16 Apr 12 Apr 18 Apr 11 Apr 17 17 Apr 19 Apr 25 Apr 18 Apr 24 18 Apr 26 May 2 Apr 25 May 1 19 May 3 May 9 May 2 May 8 20 May 10 May 16 May 9 May 15 21 May 17 May 23 May 16 May 22 22 May 24 May 30 May 23 May 29 23 May 31 Jun 6 May 30 Jun 5 24 Jun 7 Jun 13 Jun 6 Jun 12 25 Jun 14 Jun 20 Jun 13 Jun 19 26 Jun 21 Jun 27 Jun 20 Jun 26 27 Jun 28 Jul 4 Jun 27 Jul 3 28 Jul 5 Jul 11 Jul 4 Jul 10 29 Jul 12 Jul 18 Jul 11 Jul 17 30 Jul 19 Jul 25 Jul 18 Jul 24 31 Jul 26 Aug 1 Jul 25 Jul 31 32 Aug 2 Aug 8 Aug 1 Aug 7 33 Aug 9 Aug 15 Aug 8 Aug 14 34 Aug 16 Aug 22 Aug 15 Aug 21 35 Aug 23 Aug 29 Aug 22 Aug 28 36 Aug 30 Sep 5 Aug 29 Sep 4 37 Sep 6 Sep 12 Sep 5 Sep 11 38 Sep 13 Sep 19 Sep 12 Sep 18 39 Sep 20 Sep 26 Sep 19 Sep 25 40 Sep 27 Oct 3 Sep 26 Oct 2 41 Oct 4 Oct 10 Oct 3 Oct 9 42 Oct 11 Oct 17 Oct 10 Oct 16 43 Oct 18 Oct 24 Oct 17 Oct 23 44 Oct 25 Oct 31 Oct 24 Oct 30 45 Nov 1 Nov 7 Oct 31 Nov 6 46 Nov 8 Nov 14 Nov 7 Nov 13 47 Nov 15 Nov 21 Nov 14 Nov 20 48 Nov 22 Nov 28 Nov 21 Nov 27 49 Nov 29 Dec 5 Nov 28 Dec 4 50 Dec 6 Dec 12 Dec 5 Dec 11 51 Dec 13 Dec 19 Dec 12 Dec 18 52 Dec 20 Dec 26 Dec 19 Dec 25 53 Dec 27 Jan 2, 2027 Dec 26 Jan 1, 2028 2026 has 53 US week numbers and 2027 has 53. The week that holds January 1 is the last week of the old year and week 1 of the new one. See which of your own people may be leaving, before they hand in notice. [Start 30-Day Free Trial](https://app.teampredict.ai/signup) ## ISO week 1 is the week that holds the first Thursday of the year, and weeks run Monday to Sunday. ISO week 1 = the Monday to Sunday week that contains January 4 That rule is the whole system, set out in ISO 8601 and described in the [ISO week date](https://en.wikipedia.org/wiki/ISO_week_date) article. A week belongs to the year that holds most of its days, so the Thursday decides. In 2026, January 1 is a Thursday, so the week of Monday, December 29, 2025 is week 1 even though three of its days are in 2025. _Figure: Three weeks around New Year 2026, Monday to Sunday. The week of December 22 is week 52. The week of December 29 is week 1, because it holds Thursday, January 1, 2026, the first Thursday of the year. The week of January 5 is week 2._ The first Thursday of the year is in week 1, so a week that holds January 1 only counts as week 1 when January 1 is Monday to Thursday. ISO writes a day as a year, a week and a weekday number from 1 for Monday to 7 for Sunday. Monday, November 2, 2026 is 2026-W45-1. The calculator shows that form under the week number, which is handy for filenames and for systems that sort dates as text. ## A 53-week year happens about every five or six years, and 2026 is one. A normal year is 52 weeks and 1 day, so the calendar slides by a day every year, or by two in a leap year. When the slide pushes a Thursday into the last days of December, the year gets a 53rd week. The years with 53 weeks are those that start on a Thursday, plus leap years that start on a Wednesday. From 2020 to 2032 that is 2020, 2026 and 2032. _Figure: The number of ISO weeks in each year from 2020 to 2032. 2020 has 53, 2021 has 52, 2022 has 52, 2023 has 52, 2024 has 52, 2025 has 52, 2026 has 53, 2027 has 52, 2028 has 52, 2029 has 52, 2030 has 52, 2031 has 52, 2032 has 53. The years with a 53rd week are 2020, 2026, 2032._ Years with 53 weeks are marked in amber: 2020, 2026, 2032. So the ISO year 2026 has 53 weeks. Its week 1 starts on Monday, December 29, 2025, and its week 53 ends on Sunday, January 3, 2027. The ISO year 2027 has 52 weeks and starts on Monday, January 4, 2027. Anyone who reports by week should expect a week 53 in 2026 and none in 2027, and check any weekly total that is compared with the same week a year earlier. ## The US system starts the week on Sunday and counts the week with January 1 as week 1. Excel's [WEEKNUM](https://support.microsoft.com/en-us/excel/functions/weeknum-function) function, with its default setting, works this way: the week begins on Sunday, and the week that contains January 1 is week 1, whatever day of the week that is. Microsoft's separate [ISOWEEKNUM](https://support.microsoft.com/en-us/excel/functions/isoweeknum-function) function returns the ISO number instead. The US numbering restarts on January 1, so the week that crosses New Year gets two numbers: December 27, 2026 to January 2, 2027 is week 53 for the days in 2026 and week 1 for January 1 and 2 in 2027. The US table in the tool lists that week as week 53 under 2026 and as week 1 under 2027. _Figure: Four dates and their week numbers. Thursday, January 1, 2026: ISO week 1 of 2026, US week 1 of 2026. Sunday, November 1, 2026: ISO week 44 of 2026, US week 45 of 2026. Thursday, December 31, 2026: ISO week 53 of 2026, US week 53 of 2026. Friday, January 1, 2027: ISO week 53 of 2026, US week 1 of 2027._ The systems agree on most days of the year and part ways around New Year and on Sundays. In 2026 the two systems give the same number from Monday to Saturday, and a Sunday is one higher in the US system, because the US week starts a day before the ISO one. Near New Year they part ways: January 1, 2027 is in week 53 for ISO and week 1 for the US system. Pick the system your report, your payroll or your supplier uses, and keep using it all year. A table that mixes the two is a week out on some days. In Excel or Google Sheets With the date in A1, `=ISOWEEKNUM(A1)` returns the ISO week number and `=WEEKNUM(A1)` the US one. To get the ISO number from WEEKNUM, give it return type 21: `=WEEKNUM(A1,21)`. ## Use the tables to find the dates of any week number before you plan around it. The week table under the tool lists every week of two years, with the first and last day of each. It opens on 2026 and 2027, jumps to the years of a date you pick, and the Earlier years and Later years buttons move it by two. Weekly production plans, sprint calendars, delivery windows and holiday rotas are all written as “week 44”, and the table turns that into a start date and an end date without counting on a calendar. - For the days between two dates, use the [days between dates calculator](https://www.teampredict.ai/tools/days-between-dates-calculator). - To step a date forward by whole weeks, use the [date calculator](https://www.teampredict.ai/tools/date-calculator). - To count only working days in a stretch of weeks, use the [business days calculator](https://www.teampredict.ai/tools/business-days-calculator). - For overtime inside a workweek, the [time card calculator](https://www.teampredict.ai/tools/time-card-calculator) totals the hours. ## A week number tells you when the work is due, not who will still be there to do it. Plans written in weeks assume the same people turn up in week 12 as in week 1. TeamPredict reads public LinkedIn signals to flag resignation risk early, so a gap in a plan shows up as a warning while there is still time to talk. ## Methodology & sources The formula this calculator uses is shown in full above, and every assumption is an input you control. There are no hidden industry presets. All math runs in your browser; nothing you enter is stored or sent to a server. For the reasoning behind the formula and its edge cases, see: - [Microsoft: WEEKNUM function (Excel)](https://support.microsoft.com/en-us/excel/functions/weeknum-function) - [Microsoft: ISOWEEKNUM function (Excel)](https://support.microsoft.com/en-us/excel/functions/isoweeknum-function) - [ISO week date (Wikipedia)](https://en.wikipedia.org/wiki/ISO_week_date) ## Frequently asked questions What week number is it today? The calculator above opens on today's date and shows the week number right away, in the system you have chosen. As an example, Monday, November 2, 2026 is week 45 in both the ISO and the US system, and the week runs from Monday, November 2 to Sunday, November 8 in ISO terms. How is the ISO week number calculated? ISO 8601 weeks run from Monday to Sunday, and week 1 is the week that holds the year's first Thursday, which is the same as the week that holds January 4. Every later week adds one. A year has 52 or 53 weeks, and the days at the very start or end of a calendar year can belong to the neighbouring year's week. How many weeks are in a year? 52 or 53 in the ISO system. 2026 has 53 weeks, and week 53 ends on Sunday, January 3, 2027. 2027 has 52. Of the years from 2020 to 2032, only 2020, 2026 and 2032 have 53. A plain year is 52 weeks and 1 day, or 2 days in a leap year, and that extra day is why a 53rd week turns up about every five or six years. What is the difference between the ISO and the US week number? The week starts on a different day and week 1 is defined differently. In the ISO system the week starts on Monday and week 1 holds the first Thursday. In the US system, which Excel's WEEKNUM uses by default, the week starts on Sunday and week 1 is the week that holds January 1. In 2026 they agree from Monday to Saturday, and a Sunday is one higher in the US system. Why is January 1 sometimes in week 52 or 53 of the last year? Because ISO week 1 is the week with the first Thursday. January 1, 2027 is a Friday, so its week has only three days of 2027 and belongs to ISO week 53 of 2026. Week 1 of 2027 starts on Monday, January 4. January 1, 2026 is a Thursday, so week 1 of 2026 starts back on Monday, December 29, 2025. How do I get the week number in Excel or Google Sheets? With the date in A1, =ISOWEEKNUM(A1) gives the ISO week number. =WEEKNUM(A1) gives the US number, with weeks starting on Sunday, and =WEEKNUM(A1,21) gives the ISO number too. Google Sheets has the same functions. What dates are in week 44 of 2026? Type 44 into the Week box under Find the dates of a week number, choose the year and read the answer. In the ISO system week 44 of 2026 runs from Monday, October 26 to Sunday, November 1. The tables below the tool list every week of 2026 and 2027 the same way, with the start and end dates. Can I print the week numbers for the year? Yes. Press Print the ISO week table (or Print the US week table) under the tool, and only the table prints, with two years side by side and the current week marked. The Earlier years and Later years buttons move it to any other pair of years. ## Turnover is cheaper to prevent than to calculate. TeamPredict flags resignation risk early from public LinkedIn signals, giving you lead time to retain your best people before they hand in notice. [Start 30-Day Free Trial](https://app.teampredict.ai/signup) No charge today · Cancel anytime ## Keep reading [Julian Date Calendar The day of the year for any date, 001 to 366, with the year as a printable table. Read more](https://www.teampredict.ai/tools/julian-date-calendar) [Date Calculator Add or subtract days, weeks, months or years from any date and see the weekday it lands on. Read more](https://www.teampredict.ai/tools/date-calculator) [Business Days Calculator Working days between two dates, or a date plus business days, skipping weekends and US federal holidays. Read more](https://www.teampredict.ai/tools/business-days-calculator)