The tutorial shows how to build an amortization schedule in Excel to detail periodic payments on an amortizing loan or mortgage. 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. I would like to be able to calculate the remaining amount of loan due after each payment on a loan with irregular payment dates and irregular amounts. Adding extra principal payments in order to pay off the loan earlier than the loan contract calls for. In this tutorial we will add this feature. This calculator will help you determine the balance of a loan when payments have been different than the negotiated terms. This Excel spreadsheet makes it easy to view the amortization of a home loan with optional extra monthly payments. No. Due Date, Due Payment, Extra Payment (Recurring), Extra Payment (Irregular), Interest Paid, Principal Paid, Balance.