EOMONTH is part of the Analysis Toolpak add-in, which you need to
activate by means of Tools|Add-Ins.

Othwerwise, invoke the equivalent:

=DATE(YEAR(A1),MONTH(A1)+1,0)

David wrote:
I am building a spreadsheet that requires it to automatically generate the
last day of the month (for any month). I found the EOMonth function and every
time I use it all it returns is the "#NAME?" error message. I even tried hard
coding the function (=EOMonth("01/01/2006",0)), which should return
"01/31/2006" but just returns the error message "#NAME?".

Does anyone know how to get this to work?