Microsoft Excel can help you manage your finances. Use Excel formulas to calculate interest on loans, savings plans, down payments, and more.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. One way is to download Microsoft's Amortization Schedule template and replace the sample data with your own. Calculating Interest and Principal in a Single Payment. PMT (Payment Function): It calculates the fixed monthly payment for a loan based on the interest rate, loan term, and loan amount. What is an Amortization Schedule? Create a Loan Amortization Schedule in Excel and include optional extra payments.