A factorial expression, e.g. 5! is evaluated 5*4*3*2*1.

In Excel, this can be expressed as =FACT(5)

I want to do something similar, but a little different: 5+4+3+2+1

E.g. Year to date could be results for June + May + April + March + February
+ January, where Month(TODAY) gives 06 as June and then simply recalculates
the month sensitive formulas based on each month below this number, returning
the total of all evaluations.

Ideally I'd like to manage this within a formula, without resorting to VBA.
Any ideas?

Tom.

P.S. Many thanks for any attempts - regardless of whether they solve my
problem!