Mortgage Payoff Calculator

Where an extra payment actually lands

A mortgage payment is split in a fixed order: interest first, principal second.

monthly interest = remaining balance × (rate ÷ 12)
principal paid   = payment − interest

Interest is charged on whatever balance exists that month, so paying principal down early removes interest from every future month, not just the current one. That is why the effect compounds: each extra $100 lowers the balance, which lowers next month's interest, which makes more of the regular payment go to principal.

On the default example the regular payment is $2,025.62 and the first month's interest is $1,625.00 — only $400.62 of that payment touches principal. An extra $200 is therefore a 50% increase in principal reduction for that month, and it keeps paying.

Worked example: $200 a month

$300,000 balance, 6.5%, 25 years remaining, $200 extra each month:

1. Scheduled payment: $2,025.62 (principal and interest only)
2. Payoff without extras: 300 months (25 years), $307,686.45 of interest
3. Payoff with $200 extra: 243 months (20 years 3 months), $239,644.50 of interest
4. Time saved: 57 months — 4 years 9 months
5. Interest saved: $68,041.95
6. Total extra cash paid in: 200 × 243 = $48,600

The $48,600 is not a cost on top of the loan — it is principal you owed either way, paid earlier. The actual benefit is the $68,041.95 of interest you never pay.

A lump sum versus a bigger monthly payment

Same loan, two ways to attack it:

A $10,000 lump sum beats roughly four years of $200 monthly payments, because every dollar of it starts saving interest in month one. Monthly discipline wins over a longer horizon: $500 a month saves more than three times what the $10,000 lump does, but only if you keep it up for 16 years.

The savings are not linear

Doubling the extra payment does not double the saving, because the loan gets shorter and there are fewer months left to save interest on:

• $100 a month: $38,719 of interest saved over 268 months
• $250 a month: $80,245 saved over 232 months
• $500 a month: $125,588 saved over 191 months
• $1,000 a month: $176,305 saved over 143 months

Going from $500 to $1,000 adds about $50,700 of interest saving, not the $125,588 the first $500 produced. The first dollars are the most valuable, which is also why a lump sum early in the loan outperforms the same total spread over years.

Biweekly payments are the same trick

Paying half your monthly payment every two weeks gives 26 half-payments a year — 13 full payments instead of 12. On this loan that is an extra $2,025.62 a year, roughly equivalent to adding $169 a month to principal. Lenders often charge a setup fee for a "biweekly program" that just holds your money and pays monthly; you can get the same result for free by adding that amount to your regular payment.

Before you send extra money

• Check for a prepayment penalty. Rare on conventional US mortgages, common on some commercial and hard-money loans.
• Confirm the servicer applies extras to principal. Some hold them in a suspense account until the next due date, which removes the interest benefit.
• Keep your escrow current. Extra payments do not touch taxes and insurance, and a shortage in escrow is a separate bill.
• Compare against other uses of the money. At 6.5%, every extra dollar returns a guaranteed 6.5% before tax. A 4% savings account does not beat that; paying off higher-rate debt first does.

How to use this calculator

1. Enter the remaining principal from your latest statement — not the original loan amount.
2. Enter the interest rate and the years left on the loan.
3. Add the extra monthly principal you are considering.
4. Optionally add a one-time payment applied to principal in the first month.
5. Read the payoff time and the interest saved, then open the table to see what $100, $250, $500, and $1,000 a month would each do.

Frequently asked questions

Does paying extra on my mortgage really save interest?

Yes, and the effect compounds. Every dollar of extra principal removes interest from all remaining months. On $300,000 at 6.5% with 25 years left, $200 a month saves $68,042 of interest and shortens the loan by 4 years 9 months.

Is it better to pay extra monthly or in a lump sum?

A lump sum is better per dollar, because it starts saving interest immediately: $10,000 today saves $37,551. The same $10,000 paid as $200 a month arrives over four years, and each dollar only prevents interest from its own payment date onward — so it saves less. Monthly payments win on total amount paid in, not on efficiency.

What is the payoff on a $300,000 mortgage at 6.5%?

With 25 years remaining and no extra payments, the balance clears in 300 months and you pay $307,686 of interest on top of the $300,000. At $200 extra a month, it clears in 243 months with $239,645 of interest.

Will extra payments lower my required monthly payment?

No. Extra principal shortens the term but leaves the scheduled payment unchanged, unless you ask the servicer to reamortize — which most will not do on a fixed-rate loan without a modification. Only a refinance resets the payment.

Do biweekly payments pay off a mortgage faster?

Yes, because 26 half-payments equal 13 full payments a year. It is the same as adding about one-twelfth of your payment to principal every month — around $169 on a $2,025 payment. Skip paid biweekly programs and do it yourself for free.

Can I pay off my mortgage too fast?

There are only two real risks: a prepayment penalty, and tying up cash you may need for emergencies. Keep an emergency fund first, then compare the guaranteed return of extra principal against higher-rate debt and any tax deductions you would lose.

Data sources: Payments use the standard amortization formula, and the simulation applies extra principal in the month paid, which is how US servicers apply it when instructed. Interest is charged at rate ÷ 12 on the remaining balance each month. No prepayment penalties, escrow adjustments, or lender fees are modeled. All figures come from the calculator above and can be reproduced with the same inputs. For the month-by-month split, see the amortization schedule calculator; if your rate is well above the market, compare the refinance calculator before committing extra cash.