Mortgage Payoff Calculator

At its core, this calculator compares two amortization schedules side by side: your original loan schedule with the standard monthly payment, and a revised schedule that applies your extra payment directly to the principal balance each month. Because mortgage interest is calculated on the remaining principal, every dollar you send early reduces the base on which future interest is charged. This compounding effect means that even a modest extra payment — say $100 or $200 per month — can eliminate years of payments and save tens of thousands of dollars in interest over the life of a typical 30-year mortgage.

The key inputs are your current loan balance, your interest rate, the remaining term, and the extra monthly amount you plan to add. The calculator first reconstructs your standard amortization table so it knows your baseline monthly payment and payoff date. It then rebuilds the table with the extra payment applied to principal each period, tracking how the accelerated principal reduction shortens the schedule. The difference in total interest paid between the two schedules is your interest savings figure — the single most compelling number for most homeowners considering early payoff.

Several factors have an outsized effect on how powerful extra payments are. Your interest rate is the biggest lever: at 7% a 30-year loan accrues far more interest per month than at 4%, so extra payments buy more relief at higher rates. Timing also matters enormously — extra payments made early in the loan's life attack the balance when the interest-to-principal ratio in each payment is at its highest, producing the largest savings. Extra payments made in the final years of a loan, when most of each payment is already principal, return comparatively little. This is why the calculator is most valuable when you run it at the start of homeownership or after a refinance rather than year 25.

A common mistake homeowners make is assuming their lender automatically applies extra funds to principal. In reality, many servicers hold excess funds in a suspense account or apply them toward next month's payment instead. To ensure your extra payment reduces principal immediately, always specify 'apply to principal' in writing or via your lender's online portal, and verify it on your next statement. Another mistake is overlooking mortgage prepayment penalties, which some older loan contracts include. Always confirm your loan is penalty-free before committing to an extra-payment strategy — the calculator's interest savings number assumes zero penalty costs.