Mortgage Payoff Calculator - Google Sheets

Everyone says “pay extra on your mortgage” like it’s obvious advice, but nobody shows you the math. How much would an extra $100 per payment actually save? What about switching to bi-weekly payments? Would throwing a tax refund at the principal make a meaningful dent? This Google Sheets mortgage payoff calculator answers all of those questions instantly, with the full amortization schedule to back it up.

Enter your loan details — original amount, annual interest rate, start date, loan term, and payment frequency (monthly, bi-weekly, or weekly). The calculator immediately shows your scheduled payment plan: monthly payment, total number of payments, payoff date, total interest paid, and total cost of the loan. That’s your baseline. Then you add extra payments in up to three ways: additional amount on every payment, extra amount every 12th payment (great for an annual bonus), or a one-time lump sum at a specific payment number. The Actual Payments section recalculates everything and shows you the new payoff date, new total interest, and — the numbers that’ll make you smile — years saved and total amount saved.

A dynamic chart plots your loan balance, cumulative principal paid, and cumulative interest over time. You can literally watch the interest curve flatten as you increase extra payments. The amortization schedule below breaks every single payment down month by month: payment number, beginning principal, scheduled payment, extra payment, actual payment, principal paid, interest paid, cumulative totals, and ending principal. Nothing hidden, nothing rounded — every dollar accounted for.

Since it’s a Google Sheets template, you can access it from any device and share it with your partner to explore scenarios together. It also includes the Excel version if you prefer working offline. No apps to install, no financial advisor fees — just a spreadsheet that turns “I should probably pay extra” into “here’s exactly how much that saves me.”