Could you explain your question in more detail? I would like to help but I'm not sure I understand. Are you asking how to amortize the interest on the amount of payments of installments on credit line payments? I'm afraid it is a fixed amount, but the rate is always variable tied to prime and always variable based on a number of factors such as how much other outstanding credit is on your line; how much is accrued on "months same as cash" that you have in forebearance, etc. and it is not as simple as you are trying to make it. (Trust me I used to be a banker and I had a hard time explaining it to people who had finance degrees). Did I capture a little bit of what you are asking??