Mortgage Extra Payment Simulator
Simulate extra monthly principal payments on your mortgage to see exactly how much interest and time you'd save, month by month.
New payoff time
20 years, 3 months
Time saved
4 years, 9 months
Interest saved
$68,042
Total interest with extra payments
$239,645
Compares your regular payment schedule against the same schedule plus your extra monthly amount, both applied entirely to principal — this assumes your lender applies extra payments to principal immediately with no prepayment penalty, which isn't universal, so confirm with your loan servicer.
About this tool
How to use it
- Enter your current remaining loan balance, interest rate, and remaining term (not the original loan amount or original term — the current numbers from your latest statement).
- Enter an extra amount you'd pay every month on top of your regular payment.
- Read the new payoff time, the time saved, and the interest saved compared to your current schedule with no extra payments.
- Click Simulate Payoff, or just keep typing — everything updates live.
Why it matters
Extra payments toward a mortgage go entirely toward principal, which means every dollar of extra payment stops accruing interest for the rest of the loan — even a modest extra amount can save years and tens of thousands in interest, because mortgage interest compounds on a shrinking balance for decades. Seeing the actual number makes it concrete instead of an abstract 'you should pay extra' suggestion.
When to use it
Deciding whether to direct spare cash toward extra mortgage payments versus another use (investing, other debt). Comparing a few different extra-payment amounts to find one that fits the budget while still meaningfully shortening the loan. Understanding how much a specific extra payment amount actually changes the payoff timeline before committing to it.
Good to know
This simulates a full month-by-month amortization twice — once with your regular payment only, once with the extra amount added every month — and compares the two, rather than using an approximation formula. It assumes every extra dollar goes to principal immediately with no prepayment penalty, which is standard for most modern mortgages but not universal — some loans have prepayment penalties or apply extra payments differently, so confirm with your loan servicer before relying on this for a specific payoff date. It also assumes the extra payment amount stays constant every month for the life of the loan.
Common questions
Do extra payments always go straight to principal?
For most modern mortgages, yes — but not universally. Some loans have prepayment penalties, or a servicer might apply an extra payment to next month's payment instead of current principal unless you specifically instruct otherwise. Always confirm how your specific lender handles extra payments.
Why does a relatively small extra payment save so much interest?
Because mortgage interest is calculated on the remaining balance every month for potentially decades — reducing that balance sooner means every one of the following months accrues interest on a smaller number, and those small reductions compound over the life of a long loan.
Should I pay extra on my mortgage or invest the money instead?
This depends on your mortgage rate versus your expected investment return, your risk tolerance, and other factors like an emergency fund and higher-interest debt — this tool only shows what extra mortgage payments do to your loan, it doesn't compare that against other uses of the same money.
What if I want to pay a one-time lump sum instead of a recurring extra amount?
This calculator only models a fixed extra amount paid every month for the rest of the loan, not a one-time lump-sum payment — a lump sum would have a similar but smaller effect (front-loaded rather than spread across every remaining payment).
Is this financial advice?
No — this is a mortgage amortization calculation based on the numbers you enter. It doesn't account for your full financial situation, tax implications, or whether paying down this specific debt is the best use of extra money for you.