The first formula I gave you doesn't seem to work across multiple years only
within a specific year, I don't know why so try this one instead:

=AVERAGE(IF((A1:A100>=DATE(YEAR(E4),MONTH(E4),1))*(A1:A100<=DATE(YEAR(F4),MONTH(F4),1)),B1:B100))
or
=AVERAGE(IF((A1:A100>=DATE(YEAR(E4),MONTH(E4),1))*(A1:A100<=DATE(YEAR(F4),MONTH(F4)+1,1)-1),B1:B100))
again enter using Ctrl+Shift+Enter

HTH
Jean-Guy

"Daniel9684" wrote:

> I have a simple spreadsheet, in columns A and B are months of the year (from
> Jan 90 to present) and the Annual Inflation Rates for those years...
>
> In cell E4, I enter Month X, and in F4 I enter Month Y
>
> I need to work out the average of the corresponding inflation rates BETWEEN
> those two months
>
> e.g. if X is Jan 90 and Y is March 90, I need to find out the average of the
> inflation rate for Jan Feb and Mar 90.
>
> Anyone think they might be able to help me? I'm completely stumped!
>
> Thanks
> Daniel
>