modified following business day convention

[Don]

It's a businness day function where if using EDATE plus Sat/Sun->Mon takes
you into the next month, then it goes to the preceeding business day

 

[Ron Rosenfeld]

It's a businness day function where if using EDATE plus Sat/Sun->Mon takes
you into the next month, then it goes to the preceeding business day

Perhaps:

=IF(MONTH(WORKDAY(EDATE(A1,NumMnths)-1,1))=MONTH(EDATE(A1,NumMnths)),
WORKDAY(EDATE(A1,NumMnths)-1,1),WORKDAY(EDATE(A1,NumMnths),-1))

will work for you?
--ron