## How to use the WEEKNUM function

The WEEKNUM function calculates a given date's week number based on a return_type parameter that determines which day the week begins.

Formula in cell D3:

=WEEKNUM(B3,C3)

You also have the option to choose which system to use, see the [return_type] argument.

System 1 |
Week 1 is the week that contains January 1. |

System 2 |
Week 1 is the week that contains the first Thursday of the year. (European week numbering system). |

### Excel Function Syntax

WEEKNUM(*serial_number,[return_type]*)

### Arguments

serial_number |
Required. A date. If you enter the date in the function then use the DATE function to calculate the correct serial_number. |

[return_type] |
Optional. A number determining which day the week begins. If omitted, 1 is used. |

The following table shows what the LOGEST function returns if [stats] argument is TRUE.

[return_type] |
Week starts on |
System |

1 |
Sunday | 1 |

2 |
Monday | 1 |

11 |
Monday | 1 |

12 |
Tuesday | 1 |

13 |
Wednesday | 1 |

14 |
Thursday | 1 |

15 |
Friday | 1 |

16 |
Saturday | 1 |

17 |
Sunday | 1 |

21 |
Monday | 2 |

### Comments

The WEEKNUM function returns #NUM! error if:

- serial_number is out of range.
- [return_type] is out of range.

### 'WEEKNUM' function examples

The following 4 articles contain the WEEKNUM function.

Count unique distinct values within same week, month or year

The array formula in cell E3 counts unique distinct items for all dates within the same week. Example, week 2 […]

The array formula in cell E3 counts unique distinct items for all dates within the same week. Example, week 2 […]

Filter duplicates within same date, week or month

The image above demonstrates a formula in cell E3 that extracts duplicate items if they are on the same date. […]

The image above demonstrates a formula in cell E3 that extracts duplicate items if they are on the same date. […]

Highlight a date occuring [Conditional formatting]

Excel has a built-in feature that allows you to highlight dates if a given condition is met. Section 1 below […]

Excel has a built-in feature that allows you to highlight dates if a given condition is met. Section 1 below […]

Time sheet for work

I have built a sheet to track time at work. It is very simple, there are 13 sheets, one for […]

I have built a sheet to track time at work. It is very simple, there are 13 sheets, one for […]

## Functions in this article

### Functions in 'Date and Time' category

The WEEKNUM function function is one of many functions in the 'Date and Time' category.

Returns a number that acts as a date in the Excel environment.

Returns the number of days, months, or years between two dates. The DATEDIF function exists in order to ensure compatibility with Louts 1-2-3.

Returns an Excel date value (serial number) based on a date stored as text.

Extracts the day as a number from an Excel date.

Calculates the number of days between two dates.

Returns a date determined by a start date and a number representing how many months.

Returns an Excel date for the last day of a given month using a number and a start date.

Returns an integer representing the hour of an Excel time value.

Returns a whole number representing the minute based on an Excel time value. The returned number is ranging from 0 to 59.

Extracts the month as a number from an Excel date.

Returns the number of working days between two dates, excluding weekends. It also allows you to ignore a list of holiday dates that you can specify.

Calculates the number of working days between two dates, excluding weekends.

Returns the current date and time.

Returns an integer representing the second based on an Excel time value

Returns a decimal value between 0 (zero) representing 12:00:00 AM and 0.99988426 representing 11:59:59 P.M.

Returns a decimal number based on a text string.

Returns the Excel date (serial number) of the current date.

Converts a date to a weekday number from 1 to 7.

Calculates a given date's week number based on a return_type parameter that determines which day the week begins.

Returns a date based on a start date and a given number of working days (nonweekend and nonholidays).

Converts a date to a number representing the year in the date.

Returns the fraction of the year based on the number of whole days between a start date and an end date.

### Excel function categories

Excel functions that let you resize, combine, and shape arrays.

Functions for backward compatibility with earlier Excel versions. Compatibility functions are replaced with newer functions with improved accuracy. Use the new functions if compatibility isn't required.

Perform basic operations to a database-like structure.

Functions that let you perform calculations to Excel date and time values.

Let's you manipulate binary numbers, convert values between different numeral systems, and calculate imaginary numbers.

Calculate present value, interest, accumulated interest, principal, accumulated principal, depreciation, payment, price, growth, yield for securities, and other financial calculations.

Functions that let you get information from a cell, formatting, formula, worksheet, workbook, filepath, and other entitites.

Functions that let you return and manipulate logical values, and also control formula calculations based on logical expressions.

These functions let you sort, lookup, get external data like stock quotes, filter values based a condition or criteria, and get the relative position of a given value in a specific cell range. They also let you calculate row, column, and other properties of cell references.

You will find functions in this category that calculates random values, round numerical values, create sequential numbers, trigonometry, and more.

Calculate distributions, binomial distributions, exponential distribution, probabilities, variance, covariance, confidence interval, frequency, geometric mean, standard deviation, average, median, and other statistical metrics.

Functions that let you manipulate text values, substitute strings, find string in value, extract a substring in a string, convert characters to ANSI code among other functions.

Get data from the internet, extract data from an XML string and more.

## Excel categories

Latest updated articles.

More than 300 Excel functions with detailed information including syntax, arguments, return values, and examples for most of the functions used in Excel formulas.

More than 1300 formulas organized in subcategories.

Excel Tables simplifies your work with data, adding or removing data, filtering, totals, sorting, enhance readability using cell formatting, cell references, formulas, and more.

Allows you to filter data based on selected value , a given text, or other criteria. It also lets you filter existing data or move filtered values to a new location.

Lets you control what a user can type into a cell. It allows you to specifiy conditions and show a custom message if entered data is not valid.

Lets the user work more efficiently by showing a list that the user can select a value from. This lets you control what is shown in the list and is faster than typing into a cell.

Lets you name one or more cells, this makes it easier to find cells using the Name box, read and understand formulas containing names instead of cell references.

The Excel Solver is a free add-in that uses objective cells, constraints based on formulas on a worksheet to perform what-if analysis and other decision problems like permutations and combinations.

An Excel feature that lets you visualize data in a graph.

Format cells or cell values based a condition or criteria, there a multiple built-in Conditional Formatting tools you can use or use a custom-made conditional formatting formula.

Lets you quickly summarize vast amounts of data in a very user-friendly way. This powerful Excel feature lets you then analyze, organize and categorize important data efficiently.

VBA stands for Visual Basic for Applications and is a computer programming language developed by Microsoft, it allows you to automate time-consuming tasks and create custom functions.

A program or subroutine built in VBA that anyone can create. Use the macro-recorder to quickly create your own VBA macros.

UDF stands for User Defined Functions and is custom built functions anyone can create.

A list of all published articles.

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