I gather you are saying that you are paying a fixed amount plus interest
every period. So if, for example, you have a $100,000 loan, you pay $1000
plus interest every month. Is that correct?
If so, your amortization term is simply Principal/Payment.
If what you are asking for is a schedule of interest charges each period,
the easiet is to build it your self. Interest amount each period is:
=AmountOutstanding*IntRate/PaymentsPerYear
Regards,
Fred