Extra Payment Mortgage Calculator

How the calculator works

Enter five inputs: original loan amount, original mortgage term in years, years remaining on your mortgage, the extra monthly payment you want to model, and your interest rate. The calculator first computes your scheduled monthly principal-and-interest payment using standard amortization math. It then builds the full amortization schedule, switching from your scheduled payment to your accelerated payment (scheduled plus extra) at the point in the schedule that matches where you currently sit. The summary at the top shows scheduled vs. accelerated totals and the difference between them — your savings.

Why extra payments save so much interest

Mortgages amortize on a curve. In the early years, most of your monthly payment goes to interest; only a small slice reduces principal. As the loan ages, that ratio flips. Every extra dollar you apply to principal eliminates all future interest that would have accrued on that dollar for the remaining life of the loan. On a 30-year loan in its first decade, an extra dollar of principal can prevent two or three dollars of future interest. That compounding effect is why extra payments deliver larger savings than the dollar amounts suggest at first glance.

Estimating an early payoff without extra payments

The calculator also works for estimating a basic early payoff. Enter '0' as your additional payment, fill in years remaining, and the Total Scheduled Payments line shows your remaining obligation if you continue making scheduled payments only. This is useful when planning a refinance, a sale, or a lump-sum payoff in the future and you want to see what the total cost looks like under different scenarios.

What this calculator does not include

The amounts shown are principal and interest only. They do not include property taxes, homeowners insurance, mortgage insurance, HOA dues, or any escrow components. Your actual monthly mortgage payment is usually higher than the scheduled principal-and-interest figure shown here. The savings figure is also pre-tax — if you currently deduct mortgage interest on your federal return, paying off faster reduces that deduction. Consult a tax advisor to model the after-tax savings for your specific situation.

Where to send the extra payment

When you make extra payments, make sure your servicer applies the extra to principal — not to the next month's regular payment or to an escrow account. Most servicers have a specific field on their payment portal for principal-only payments, or a separate mailing instruction. If you simply add the extra amount to your normal payment without specifying, some servicers will treat it as a partial advance payment of the following month, which does not reduce principal faster. Always confirm with your servicer how to direct the extra dollars.

Other ways to accelerate payoff

Adding a fixed monthly extra is just one strategy. Other approaches include making one extra full mortgage payment per year (often achieved through biweekly payments — 26 half-payments equals 13 monthly payments), applying tax refunds or bonuses as lump-sum principal payments, or refinancing into a shorter term such as a 15-year loan that forces faster amortization. Each has different cash-flow implications. The right strategy depends on your stability of income, your other financial goals, and your interest rate environment.