Debt Ageing using if in excel

I want to create an excel sheet of our customers balances which will automatically calculate how much is due based on the credit terms and when they are due.

in one sheet i have the data, with the customers balances each month and credit terms. and in the other sheet should be the analysis of when the balance is due (monthly basis). using IF in excel, how can i automatically put how much is due on a specific month for each customer.. anybody pls help...