---
title: "WEEKNUM function in Excel: syntax and examples | PracticeExcel"
description: "How to use WEEKNUM in Excel and Google Sheets: US and ISO week numbers, and why Jan 1 can fall in week 53."
canonical_url: "https://practiceexcelonline.com/functions/weeknum"
locale: en
meta:
  "og:description": "How to use WEEKNUM in Excel and Google Sheets: US and ISO week numbers, and why Jan 1 can fall in week 53."
  "og:image": "https://practiceexcelonline.com/_og/d/c_Page%2Ctitle_~V0VFS05VTSBmdW5jdGlvbiBpbiBFeGNlbDogc3ludGF4IGFuZCBleGFtcGxlcw%2Cdescription_~SG93IHRvIHVzZSBXRUVLTlVNIGluIEV4Y2VsIGFuZCBHb29nbGUgU2hlZXRzOiBVUyBhbmQgSVNPIHdlZWsgbnVtYmVycywgYW5kIHdoeSBKYW4gMSBjYW4gZmFsbCBpbiB3ZWVrIDUzLg%2Ceyebrow_Excel%2Bfunctions%2Csite_practiceexcel%2Ccode_~V0VFS05VTShzZXJpYWxfbnVtYmVyLCBbcmV0dXJuX3R5cGVdKQ%2Cp_Ii9mdW5jdGlvbnMvd2Vla251bSI%2Cs_e4IWYnPSELGn2YF1.png"
  "og:image:height": "600"
  "og:image:type": image/png
  "og:image:width": "1200"
  "og:title": "WEEKNUM function in Excel: syntax and examples | PracticeExcel"
  "twitter:image": "https://practiceexcelonline.com/_og/d/c_Page%2Ctitle_~V0VFS05VTSBmdW5jdGlvbiBpbiBFeGNlbDogc3ludGF4IGFuZCBleGFtcGxlcw%2Cdescription_~SG93IHRvIHVzZSBXRUVLTlVNIGluIEV4Y2VsIGFuZCBHb29nbGUgU2hlZXRzOiBVUyBhbmQgSVNPIHdlZWsgbnVtYmVycywgYW5kIHdoeSBKYW4gMSBjYW4gZmFsbCBpbiB3ZWVrIDUzLg%2Ceyebrow_Excel%2Bfunctions%2Csite_practiceexcel%2Ccode_~V0VFS05VTShzZXJpYWxfbnVtYmVyLCBbcmV0dXJuX3R5cGVdKQ%2Cp_Ii9mdW5jdGlvbnMvd2Vla251bSI%2Cs_e4IWYnPSELGn2YF1.png"
---

> Index of every page on this site: [llms.txt](https://practiceexcelonline.com/llms.txt)

# **The WEEKNUM function**

Returns the week number of a date. By default weeks start on Sunday and week 1 is the week with Jan 1 in it; return type 21 gives ISO week numbers, as used in Europe.

=

WEEKNUM(

## **Syntax**

```
WEEKNUM(serial_number, [return_type])
```

<dl><dt>**serial_number **</dt>
<dd>The date to check.</dd>
<dt>**return_type **(optional)</dt>
<dd>1 or left out for weeks starting on Sunday, 2 for weeks starting on Monday, 21 for ISO weeks (Monday start, week 1 holds the first Thursday).</dd></dl>

## **Examples**

B1=WEEKNUM(DATE(2024,3,15))

|  | A | B |
| --- | --- | --- |
| 1 |  | **11** |

B1=WEEKNUM(DATE(2021,1,1))

|  | A | B |
| --- | --- | --- |
| 1 |  | **1** |

B1`=WEEKNUM(<sup>1</sup>DATE(2021,1,1),<sup>2</sup>21)`

|  | A | B |
| --- | --- | --- |
| 1 |  | **53** |

**In plain words:** The week number of <sup>1</sup>Jan 1, 2021, <sup>2</sup>counted the ISO way.

## **Questions**

<details>

<summary>

### How do I get ISO week numbers in Excel?

</summary>

Use =WEEKNUM(A2,21) or =ISOWEEKNUM(A2). ISO weeks start on Monday, and week 1 is the week that holds the first Thursday of the year.

</details>

<details>

<summary>

### Why is Jan 1 in week 53?

</summary>

With ISO weeks, the first days of January can belong to the last week of the year before. Jan 1, 2021 was a Friday, so it is in week 53 of 2020.

</details>

## **Related functions**

- [**WEEKDAY**](https://practiceexcelonline.com/functions/weekday)
- [**DATE**](https://practiceexcelonline.com/functions/date)
- [**TODAY**](https://practiceexcelonline.com/functions/today)

```json
{"@context":"https://schema.org","@graph":[{"@id":"https://practiceexcelonline.com/#identity","@type":"Organization","name":"PracticeExcel","url":"https://practiceexcelonline.com/","logo":{"@id":"https://practiceexcelonline.com/#logo"}},{"@id":"https://practiceexcelonline.com/#website","@type":"WebSite","inLanguage":"en-US","name":"PracticeExcel","url":"https://practiceexcelonline.com/","alternateName":["Practice Excel Online","PracticeExcelOnline.com"],"publisher":{"@id":"https://practiceexcelonline.com/#identity"},"workTranslation":{"@id":"https://excelopgaver.dk/#website"}},{"@id":"https://practiceexcelonline.com/functions/weeknum#webpage","description":"How to use WEEKNUM in Excel and Google Sheets: US and ISO week numbers, and why Jan 1 can fall in week 53.","name":"WEEKNUM function in Excel: syntax and examples","url":"https://practiceexcelonline.com/functions/weeknum","@type":["WebPage","FAQPage"],"breadcrumb":{"@id":"https://practiceexcelonline.com/functions/weeknum#breadcrumb"},"isPartOf":{"@id":"https://practiceexcelonline.com/#website"},"mainEntity":[{"@id":"https://practiceexcelonline.com/functions/weeknum#/schema/question/1"},{"@id":"https://practiceexcelonline.com/functions/weeknum#/schema/question/2"}],"potentialAction":[{"@type":"ReadAction","target":["https://practiceexcelonline.com/functions/weeknum"]}],"primaryImageOfPage":{"@id":"https://practiceexcelonline.com/#logo"}},{"@id":"https://practiceexcelonline.com/functions/weeknum#breadcrumb","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","name":"Home","item":"https://practiceexcelonline.com","position":1},{"@type":"ListItem","name":"Excel functions","item":"https://practiceexcelonline.com/functions","position":2},{"@type":"ListItem","name":"WEEKNUM function in Excel: syntax and examples","position":3}]},{"@id":"https://practiceexcelonline.com/functions/weeknum#article","description":"How to use WEEKNUM in Excel and Google Sheets: US and ISO week numbers, and why Jan 1 can fall in week 53.","headline":"WEEKNUM function in Excel: syntax and examples","inLanguage":"en-US","thumbnailUrl":"https://practiceexcelonline.com/_og/d/c_Page%2Ctitle_~V0VFS05VTSBmdW5jdGlvbiBpbiBFeGNlbDogc3ludGF4IGFuZCBleGFtcGxlcw%2Cdescription_~SG93IHRvIHVzZSBXRUVLTlVNIGluIEV4Y2VsIGFuZCBHb29nbGUgU2hlZXRzOiBVUyBhbmQgSVNPIHdlZWsgbnVtYmVycywgYW5kIHdoeSBKYW4gMSBjYW4gZmFsbCBpbiB3ZWVrIDUzLg%2Ceyebrow_Excel%2Bfunctions%2Csite_practiceexcel%2Ccode_~V0VFS05VTShzZXJpYWxfbnVtYmVyLCBbcmV0dXJuX3R5cGVdKQ%2Cp_Ii9mdW5jdGlvbnMvd2Vla251bSI%2Cs_e4IWYnPSELGn2YF1.png","@type":["Article","TechArticle"],"author":{"@id":"https://practiceexcelonline.com/#identity"},"image":{"@id":"https://practiceexcelonline.com/#/schema/image/1"},"isPartOf":{"@id":"https://practiceexcelonline.com/functions/weeknum#webpage"},"mainEntityOfPage":{"@id":"https://practiceexcelonline.com/functions/weeknum#webpage"},"publisher":{"@id":"https://practiceexcelonline.com/#identity"}},{"@id":"https://practiceexcelonline.com/functions/weeknum#/schema/question/1","@type":"Question","inLanguage":"en-US","name":"How do I get ISO week numbers in Excel?","acceptedAnswer":{"@type":"Answer","text":"Use =WEEKNUM(A2,21) or =ISOWEEKNUM(A2). ISO weeks start on Monday, and week 1 is the week that holds the first Thursday of the year."}},{"@id":"https://practiceexcelonline.com/functions/weeknum#/schema/question/2","@type":"Question","inLanguage":"en-US","name":"Why is Jan 1 in week 53?","acceptedAnswer":{"@type":"Answer","text":"With ISO weeks, the first days of January can belong to the last week of the year before. Jan 1, 2021 was a Friday, so it is in week 53 of 2020."}},{"@id":"https://practiceexcelonline.com/#logo","@type":"ImageObject","caption":"PracticeExcel","contentUrl":"https://practiceexcelonline.com/brand/practiceexcel/icon-512.png","inLanguage":"en-US","url":"https://practiceexcelonline.com/brand/practiceexcel/icon-512.png"},{"@id":"https://practiceexcelonline.com/#/schema/image/1","@type":"ImageObject","contentUrl":"https://practiceexcelonline.com/_og/d/c_Page%2Ctitle_~V0VFS05VTSBmdW5jdGlvbiBpbiBFeGNlbDogc3ludGF4IGFuZCBleGFtcGxlcw%2Cdescription_~SG93IHRvIHVzZSBXRUVLTlVNIGluIEV4Y2VsIGFuZCBHb29nbGUgU2hlZXRzOiBVUyBhbmQgSVNPIHdlZWsgbnVtYmVycywgYW5kIHdoeSBKYW4gMSBjYW4gZmFsbCBpbiB3ZWVrIDUzLg%2Ceyebrow_Excel%2Bfunctions%2Csite_practiceexcel%2Ccode_~V0VFS05VTShzZXJpYWxfbnVtYmVyLCBbcmV0dXJuX3R5cGVdKQ%2Cp_Ii9mdW5jdGlvbnMvd2Vla251bSI%2Cs_e4IWYnPSELGn2YF1.png","inLanguage":"en-US","url":"https://practiceexcelonline.com/_og/d/c_Page%2Ctitle_~V0VFS05VTSBmdW5jdGlvbiBpbiBFeGNlbDogc3ludGF4IGFuZCBleGFtcGxlcw%2Cdescription_~SG93IHRvIHVzZSBXRUVLTlVNIGluIEV4Y2VsIGFuZCBHb29nbGUgU2hlZXRzOiBVUyBhbmQgSVNPIHdlZWsgbnVtYmVycywgYW5kIHdoeSBKYW4gMSBjYW4gZmFsbCBpbiB3ZWVrIDUzLg%2Ceyebrow_Excel%2Bfunctions%2Csite_practiceexcel%2Ccode_~V0VFS05VTShzZXJpYWxfbnVtYmVyLCBbcmV0dXJuX3R5cGVdKQ%2Cp_Ii9mdW5jdGlvbnMvd2Vla251bSI%2Cs_e4IWYnPSELGn2YF1.png"}]}
```

## Sitemap

See the full [sitemap](https://practiceexcelonline.com/sitemap.md) for all pages.