Formualizer Docs
ReferenceFunctionsDate & Time Functions

WEEKNUM

WEEKNUM: Returns the week number of the year for a date serial.

Summary

Returns the week number of the year for a date serial.

Remarks

  • Default return_type is 1 (week starts on Sunday).
  • Supported return_type values are 1, 2, 11-17, and 21 (ISO week numbering).
  • Unsupported return_type values return #NUM!.
  • Input serials are interpreted using Excel 1900 date mapping rather than workbook 1904 interpretation.

Examples

Default week numbering
Grid
CellValue
No inputs on Sheet1.
Formula
=
Result
Not evaluated yet.
Expected
1
ISO week numbering
Grid
CellValue
No inputs on Sheet1.
Formula
=
Result
Not evaluated yet.
Expected
53

FAQ

What is special about return_type 21 in WEEKNUM?

return_type=21 switches to ISO week numbering, matching ISOWEEKNUM behavior.

Runtime metadata

Category

Date & Time

Signature

WEEKNUM(arg1: Number, arg2…: Number)

Arity

min 1, max variadic

Arguments

arg1

Number · Scalar · coercion NumberLenientText

arg2

Number · Scalar · coercion NumberLenientText

Caps

PURE

Source

crates/formualizer-eval/src/builtins/datetime/weekday_workday.rs

WEEKDAY

WEEKDAY: Returns the day-of-week index for a date serial with configurable numbering.

WORKDAY

WORKDAY: Returns the date serial that is a given number of weekdays from a start date.

On this page

SummaryRemarksExamplesRelated functionsFAQWhat is special about return_type 21 in WEEKNUM?Runtime metadata