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WEEKNUM Function

The WEEKNUM function is one of the date and time functions. It used to return the number of the week the specified date falls within the year.

The WEEKNUM function syntax is:

WEEKNUM(serial_number, [return_type])


serial_number is a number representing the date within the week, entered using the Date function or other date and time function.

return_type is a numeric value used to determine on which day the week begins. It can be one of the following:

Numeric value Week begins on System
1 or omitted 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

When return_type is set to 1-17, System 1 is used. This means that the first week in a year is the week that contains January 1.

When return_type is set to 21, System 2 is used. This means that the first week in a year is the week that contains the first Thursday of the year. System 2 is commonly used in Europe according to the ISO 8601 standard.

To apply the WEEKNUM function,

  1. select the cell where you wish to display the result,
  2. click the Insert function
    icon situated at the top toolbar,
    or right-click within a selected cell and select the Insert Function option from the menu,
    or click the
    icon situated at the formula bar,
  3. select the Date and time function group from the list,
  4. click the WEEKNUM function,
  5. enter the required arguments separating them by commas,
  6. press the Enter button.

The result will be displayed in the selected cell.

WEEKNUM Function

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