What function/formula can I use to return the previous month. Let's say cell
A1 contains just the word August. What can I put in the next cell to
return July. But will also give December if January is in A1. I am
currently doing it with the following convoluted vlookup & I'm sure there
must be an easier way.

ColG ColH ColI

12 December 12
11 November 11
10 October 10
9 September 9
8 August 8
7 July 7
6 June 6
5 May 5
4 April 4
3 March 3
2 February 2
1 January 1
0 December 0
-1 November -1
-2 October -2

Above is my vlookup range (columns G,H,I rows 3 to 17) and my formula is:

=VLOOKUP((VLOOKUP(A1,$H$3:$I$17,2,FALSE)-1),$G$3:$H$17,2,FALSE)

It works fine but I'm sure I must be missing something *really* obvious.(and
simpler:-)

Many thanks

-Jay-