It is actually quite simple. You just need to make a table in excel showing Opening Balance, adding interest and reducing through payments.Here is the link to my spreadsheet where you can calculate a loan over x years to be paid back monthly. It will give you the amortized payment amount. Step 1: Set up your amortization table. Open a new Excel sheet and create input cells for the known components of your loan. Loan Amortization Schedule outlines the interest and principal payments owed on a mortgage, including the outstanding balance.