WEEKDAY

Function Reference: WEEKDAY

Syntax
=WEEKDAY(serial_number,[return_type])
Purpose / Description
Returns a number indicating the day of the week upon which a serial date number falls.  It has been updated in later versions of Excel to support all combinations of possible weekend or non-trading days of the week
Arguments
Name Type Description
serial_number number A constant, reference or nested expression which provides the serial date number for which the calculation is to be undertaken. Any decimal portion, assumed to represent time of day, is ignored.
[return_type] number An optional constant, reference or nested expression which indicates how the weekday number is t be calculated.  Defaults to 1, if omitted.
1 1 to 7 - numbering the days Sunday through Saturday
2 1 to 7 - numbering the days Monday through Sunday
3 0 to 6 - numbering the days Monday through Sunday (originally provided for Lotus 1-2-3 compatibility)
11 1 to 7 - numbering the days Monday through Sunday - same as return_type 2
12 1 to 7 - numbering the days Tuesday through Monday
13 1 to 7 - numbering the days Wednesday through Tuesday
14 1 to 7 - numbering the days Thursday through Wednesday
15 1 to 7 - numbering the days Friday through Thursday
16 1 to 7 - numbering the days Saturday through Friday
17 1 to 7 - numbering the days Sunday through Saturday - same as return_type 1
Return Values
Type Specific Value Description
number  0 - 7 The day of the week number based on the return_type specified.
error #VALUE! if serial_number or return_type is not a number and cannot be coerced to number.
error #NUM! If the number passed in serial_number is outside the range allowed
1900 date system 0 to 2,958,465
1904 date system 0 to 2,957,003
error   Any errors referenced by arguments are returned due to propagation of error values.
Notes / Comments / Advice / Warnings
Note: The return_type values 11 to 17 were added in Excel 2007 to better handle internationalisation and alternative week management requires, such as payroll weeks which don't end on a Friday or Saturday.
Examples: Open / download sample workbook: WEEKDAY, WORKDAY, WORKDAY.INTL.xlsx