Excel 2007 : Monthly Average Formula

Hello Everyone,

I am trying to find a formula that will allow me to calculate monthly averages from my daily data.

My spreadsheet is set out as follows:

A--B
Date--Value
01/01/2000--2.18
02/01/2000--4.26
.
.
.

I have many years of data to process and have looked at other people's questions about similar problems but can't seem to apply the solutions to mine. I am not sure that pivot tables are the best option too as I want to process the monthly averages following this calculation.

Any help would be fantastic.

David