Is a one-time extra payment the same as this calculator?

No — this models a recurring extra amount added every month. A single one-time extra payment would save less overall since it only reduces the balance once rather than every month for the life of the loan.

Should I pay extra on my mortgage or invest the money instead?

It depends on your mortgage rate versus your expected investment return, and your tolerance for risk versus a guaranteed return (interest saved is effectively a guaranteed, risk-free return equal to your mortgage rate). This calculator only shows the mortgage-side savings, not an investment comparison.

What if my extra payment amount is large enough to pay off the loan almost immediately?

The simulation still runs correctly — it caps the final month's payment at whatever balance remains rather than overpaying, and stops as soon as the balance reaches zero.

Why does a small extra payment save a disproportionately large amount of interest?

Because it reduces principal starting immediately, and that reduction compounds — every future month's interest is calculated on a smaller balance than it otherwise would have been, for every remaining month of the loan.

Does this work for a fixed-rate mortgage only, or also adjustable-rate?

It assumes a constant interest rate for the remaining term, which matches a fixed-rate mortgage. For an adjustable-rate mortgage, treat the result as a snapshot based on today's rate — actual savings will shift if your rate changes.

What happens if I enter a 0% interest rate?

The calculator switches to a straight-line payoff — balance divided evenly by the number of months — since the amortization formula's usual denominator would be undefined at exactly 0%.

Can extra payments ever not save any interest?

Only if you enter $0 as the extra payment, in which case the 'with extra' schedule is identical to the original and savings show as $0 — any amount above $0 always saves some interest under this model.

Is refinancing to a shorter term better than paying extra on my current loan?

A shorter-term refinance guarantees a faster payoff but locks you into a higher required payment; extra payments on your current loan achieve a similar effect while keeping the lower required payment as a fallback if your finances change. The Mortgage Refinance Calculator can help compare the refinance path directly.

Mortgage Payoff / Extra Payment Calculator

About the Mortgage Payoff / Extra Payment Calculator

Shows how much time and interest you'd save by adding an extra amount to your regular monthly mortgage payment — comparing your current payoff schedule against one with the extra payment applied every month.

100% Free Runs in Your Browser No Sign-Up Required

How to use it

Enter your Remaining mortgage balance and current Interest rate.
Enter the Remaining term — how many years are left on your loan as it stands today.
Enter an Extra payment amount you'd add to every monthly payment.
Read the interest and time saved instantly in the result panel.

Formula

The calculator first derives your regular monthly payment from the standard amortizing-loan formula (remaining balance, rate, and remaining term). It then simulates two schedules month by month: the original one at the regular payment, and a second one where your extra amount is added to principal every month, tracking how many months each takes to reach a zero balance and how much total interest each accrues. The difference between the two is what's shown as saved.

Worked example

A $300,000 balance at 6.5% with 25 years remaining, paying an extra $200 every month, saves about $68,042 in interest and pays the loan off roughly 4 years 9 months early — cutting the term from 25 years to about 20 years 3 months.

Interest saved by extra payment amount (same $300,000 / 6.5% / 25-year example)

Interest saved by extra payment amount (same $300,000 / 6.5% / 25-year example)
Extra per month	Interest saved	Time saved
$100	$38,719	2 yr 8 mo
$200	$68,042	4 yr 9 mo
$300	$91,174	6 yr 5 mo
$500	$125,588	9 yr 1 mo

Interpreting your result

This assumes every extra dollar goes straight to principal reduction, applied consistently every month for the life of the loan. Confirm with your servicer that extra payments are actually applied that way by default — some servicers apply an extra payment toward your next due date instead of principal unless you specifically instruct otherwise, which would not produce these savings.

Recommendations

• Even a modest, sustainable extra payment compounds meaningfully over a 15-30 year term — the savings scale faster than the extra amount itself, since every dollar of avoided interest is a dollar that also stops compounding for the rest of the loan.
• Making an extra payment earlier in the loan saves more than the same extra payment made later, since more of each regular payment is going to interest early on — if you can start extra payments sooner, do.
• Check your loan for a prepayment penalty before committing to a large extra-payment strategy — most conventional US mortgages originated in recent years don't have one, but it's worth confirming with your servicer.

Frequently asked questions

No — it's an estimate using the standard amortization formula based on what you enter. Your actual schedule may differ slightly due to rounding, fees, or how your specific servicer applies payments; check your loan statement for exact figures.

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