I have a really nice Amortization Schedule built in Excel using the steps from this page: http://www.wikihow.com/Prepare-Amortization-Schedule-in-Excel It works really nicely, but I am planning to make some large payments and I would love to calculate how much interest I will save, over the life of the loan, for making these larger payment. E.g., if I pay $10k for one payment I will save $4000 in interest over the life of the loan, etc. Is there a way to calculate this?