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WEEK NUMBER GUIDE

What Week Number Is It?

To find the current week number, use the week number calculator on this site — it shows the ISO 8601 week number updated in real time. You can also calculate it by hand using the rules below.

How to find the week number of any date

The ISO week number of any date can be found in 3 steps:

  1. Find the Thursday of the same week as your date (Monday = start of week)
  2. Count which Thursday it is in the year — that is the week number
  3. If the Thursday falls in January of the next year, the week belongs to the next year

Example: What week is April 10, 2026?
April 10, 2026 is a Friday. The Thursday of that week is April 9. April 9 is the 99th day of 2026 → Thursday number: ⌈99/7⌉ = 15. Week 15.

Quick reference: first week of each month 2025–2026

MonthFirst MondayISO WeekYear
January 202530 Dec 2024W012025
February 20253 FebW062025
March 20253 MarW102025
April 202531 MarW142025
May 20255 MayW192025
June 20252 JunW232025
July 202530 JunW272025
August 20254 AugW322025
September 20251 SepW362025
October 20256 OctW412025
November 20253 NovW452025
December 20251 DecW492025
January 202629 Dec 2025W012026

In Excel or Google Sheets

To get the ISO week number of any date cell (e.g. A1) in a spreadsheet:

  • Excel: =ISOWEEKNUM(A1)
  • Google Sheets: =ISOWEEKNUM(A1)

Both functions return the ISO 8601 week number directly.

FAQ

What is the current week number?

Use the week number tool on this site for a live answer. As a reference: week 1 of 2026 starts on December 29, 2025.

How do I find the week number in Excel?

Use the ISOWEEKNUM function: =ISOWEEKNUM(A1) where A1 contains your date. This returns the ISO 8601 week number.

What week number is my birthday in 2026?

Enter your birthday into the week number calculator on this site and it will show you the ISO week number for any date.

Is week 1 always January 1?

No. ISO week 1 is the week containing January 4. January 1 can fall in week 52 or 53 of the previous year if it lands on a Friday, Saturday, or Sunday.

Related: ISO week number explained · Week numbers 2025 — full calendar · How many weeks in a year?
Week Number Calculator — current week →