Create automatic loan amortization schedule table with PMT, IPMT, PPMT formulas in Microsoft Excel 1. Download the amortization schedule from Microsoft. 2.Open the template in Excel. 3. The tutorial shows how to build an amortization schedule in Excel to detail periodic payments on an amortizing loan or mortgage. How to find a loan payment amount and build an amortization schedule. Does anyone know how to calculate the principal and interest payments after a one time extra principal payment on a mortgage in excel? Fill in the column titled "Period" with your payment dates. Input the month and year for the first payment loan within cell A8. Loan amortization schedule. 3. 4, Enter values, Loan summary.