Here is a simpler function for you to consider...

Public Function LastDayInLastMo(TargDate As Date) As Date
'get the last day of the month prior to the date in the cell
LastDayInLastMo = DateSerial(Year(TargDate), Month(TargDate), 0)
End Function

Or, perhaps even simpler, using only one function and one arithmetic
operation.

==================
Public Function LastDayInLastMo(TargDate As Date) As Date
'get the last day of the month prior to the date in the cell
LastDayInLastMo = TargDate - Day(TargDate)
End Function
===================

Yep, that is definitely a better formula to use.

--
Rick (MVP - Excel)