The WEEKNUM function in Excel is used to determine the week number of a given date. It helps you find out which week of the year a particular date falls in. This function can be especially useful in various scheduling and date-related tasks.

## Syntax

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

## Arguments

serial_number | The date for which you want to find the week number. It can be entered as a date in a recognized format, a reference to a cell containing a date, or a formula that results in a date. |

[return_type] | A number that specifies which day of the week is considered the first day of the week. This argument can take on values from 1 to 21, with different values representing different systems for determining the first day of the week. The default is 1, where Sunday is considered the first day. |

## How to Use

The WEEKNUM function is relatively simple to use. You provide it with a date, and it returns the week number for that date. Here’s the basic usage:

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=WEEKNUM(serial_number, [return_type]) |

Let’s look at a few examples:

**Example 1:**

If you want to find the week number for a date in cell A1, where Sunday is considered the first day of the week, you can use the following formula:

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=WEEKNUM(A1,1) |

This formula will return the week number for the date in cell A1 according to the system where Sunday is the first day of the week.

**Example 2:**

If you have a date like “2023-11-03” and want to find the week number, you can directly enter the date in the formula:

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=WEEKNUM("2023-11-03",1) |

This formula will return the week number for the given date, considering Sunday as the first day of the week.

**Example 3:**

If you don’t specify the return_type argument, it defaults to 1 (Sunday as the first day of the week). So, you can simply use the formula like this:

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=WEEKNUM(A1) |

It will return the week number with Sunday as the first day.

## Additional Information

The WEEKNUM function is versatile and can be helpful in various situations where you need to work with date-related data. Remember that the [return_type] argument is optional and can be adjusted according to your specific needs.

If you want to learn more about the [return_type] values and how they affect the result, you can check the official Microsoft Excel documentation or other reliable sources for a detailed explanation.