Assuming the your sheet has each month's value in a the columns B:M then:

=LOOKUP(10^10,B2:M2)-INDEX(B2:M2,COUNT(B2:M2)-1)

or

=INDEX(B2:M2,COUNT(B2:M2))-INDEX(B2:M2,COUNT(B2:M2)-1)

will return the last value minus the second last value

--
HTH

Sandy
In Perth, the ancient capital of Scotland
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"GJP" wrote in message
...
I've got a spreadsheet that tracks a number of inventory categories &
values
by month. The last column calculates the Monthly Change for each row -
this
month's inventory minus last month's inventory. Rather than change the
formula each month I thought I could use a nested IF based on the month
number, but ran into the limitation of 7 nested IFs, which is a problem
given
that there are 12 months. Anyone have a good way to do a subtraction
calculation in a cell that will have varying column references each month?
Thanks