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Mortgage Extra Payment Calculator

Find out how much sooner you'd pay off your mortgage, and how much interest you'd save, by adding extra principal payments. Compare extra monthly amounts, a one-time lump sum, or switching to biweekly payments against your standard schedule.

Your original loan amount, or your current remaining balance if you're partway through an existing mortgage.

Defaults to the current national average 30-year fixed rate. Replace it with your actual loan rate for an accurate result.

Use your original term, or the years remaining on your loan if you entered your current balance above.

Used only when Acceleration Method is set to Extra amount every month.

Used only when Acceleration Method is set to One-time lump sum.

Which payment number the lump sum is applied to, for example 12 for the one-year mark. Used only with the lump sum method.

Interest Saved
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Paid Off
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New Payoff Date
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Monthly Payment (P&I)
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Total Interest (Standard Schedule)
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Total Interest (With Extra Payments)
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Original Payoff Date
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Outstanding balance over time

Months Balance

Rates and figures last updated: July 23, 2026

Assumptions

Sources

Why extra principal payments save more than they cost

A mortgage payment is mostly interest early on and mostly principal near the end, because interest is charged each month on whatever balance is still outstanding. Every extra dollar you put toward principal removes that dollar from every remaining month's interest calculation for the rest of the loan, not just the current one. That's why an extra payment made in year 2 saves far more total interest than the same dollar amount paid in year 25: it has more remaining months left to keep saving on.

Choosing between extra monthly, lump sum, and biweekly

Extra monthly principal works best if you can sustain the habit every month; it produces the steadiest reduction because it starts compounding immediately. A lump sum is a good fit for a bonus, tax refund, or other windfall, and matters most when applied early, while the balance and remaining term are still large. Biweekly payments automate one extra payment a year without you having to pick an amount, but confirm your servicer applies each half-payment to principal right away and doesn't charge a setup or per-payment fee, since paid third-party biweekly programs have drawn regulatory scrutiny for overstating their savings.

Worked example

A $350,000 loan at 6.55% for 30 years, with an extra $200 applied to principal every month.

The standard monthly payment (principal and interest) works out to $2,223.76. Left alone, the loan pays off in 360 months with $450,553 in total interest. Adding $200 extra to principal every month pays it off in 286 months instead, 6 years 2 months early, cutting total interest to $341,100, a savings of about $109,453.

Frequently asked questions

How does an extra payment actually shorten a mortgage?

Your regular payment already splits between interest and principal each month. An extra amount you add goes entirely to principal, which lowers the balance interest gets calculated on for every month that follows, so the loan reaches zero sooner and skips all the interest it would otherwise have accrued in those final months.

Is a lump sum or steady extra payments better for paying off a mortgage early?

Both reduce principal, so the real difference is timing: a lump sum applied early in the loan removes a large amount of principal while the most future interest is still ahead of it, which can outperform smaller recurring payments spread over the same period. Steady monthly amounts are easier to sustain without a windfall. Try both modes above with your own numbers to compare.

How much do biweekly mortgage payments actually save?

A biweekly plan collects half your normal payment every two weeks, which adds up to 26 half-payments, the equivalent of 13 full monthly payments instead of 12, over a year. That one extra payment a year is what drives the savings, and this calculator simulates it on its own biweekly schedule rather than treating it as a rough monthly estimate.

Can I use this if I'm partway through my mortgage instead of just starting one?

Yes. Enter your current outstanding balance as the loan amount and the years you have left, not the original loan term, along with your actual interest rate. The math is identical either way: it's just amortizing forward from whatever principal and remaining term you give it.

What amortization method does this calculator use?

It uses the standard fixed-rate amortization formula to set the monthly payment, then rebuilds the full schedule month by month, tracking interest and principal separately for every payment. It runs that simulation twice, once as your standard schedule and once with your chosen extra payments, and compares the two directly rather than estimating the difference from a formula shortcut.

How is the new payoff date calculated?

The calculator counts how many payments it takes each schedule to reach a zero balance, then adds that many months to today's date, assuming your first payment starts this month. If you're starting from a current balance partway through an existing loan, the resulting date reflects payments counted from now, not from your original loan's start.

Does this include my escrow payment for taxes and insurance?

No. Escrow is a separate account your lender uses to pay property taxes and homeowners insurance on your behalf, and it isn't part of your loan principal, so it plays no role in the payoff date or interest savings calculated here. Only the principal and interest portion of your payment, and any extra principal you add, affects those numbers.