Excel Formula Help

I am creating a spreadsheet to keep a running total on expenditures from different accounts and cannot figure out a formula to automatically show the balance. 

I have a column where I input the account number (3 different numbers), a column with the amount of the deduction, a cell with the overall budget total and of course a cell for the current balance. I have tried an IF/Then formula; =IF(A5:A500="xxxx.AA", SUM B2-I5:I500) 

Where A5:A500 are the range of cells in the column containing one of the three account numbers, B2 is the cell containing the overall account total and I5:I500 the range of cells with the input of the expenditure, and I was wanting the balance to show in cell B3. I can't get this formula to work. Am I missing something or is there a different formula or better way to keep a running balance for multiple cells and lines? Thanks in advacne for any and all help and suggestions.