Loan Amortization Formula ; 1. This Microsoft Excel template illustrates how to create a loan amortization schedule, as well as dealing with additional payments and variable interest rates.This example teaches you how to create a loan amortization schedule in Excel. 1. We use the PMT function to calculate the monthly payment on a loan. This free Roth IRA calculator estimates your account balance at retirement and determines how much you are eligible to contribute in 2024.