Additional Payment Mortgage Calculator

A small extra payment on a mortgage does more than trim the balance by that amount. Every extra dollar goes to principal, so all later interest is charged on a smaller balance, and the saving compounds month after month. Enter your loan details and an extra monthly amount below to see the new payoff date, the time saved, the interest saved, and a year-by-year comparison of both scenarios.

Quick Answer

How to use the additional payment mortgage calculator

Five fields, one button, and the results stay hidden until you calculate.

1. Enter the loan amount: the amount borrowed, or the remaining balance for a loan you already hold. The worked example uses $300,000.
2. Enter the annual rate: the fixed rate, in percent. Zero is accepted and handled as a straight division of principal over the term.
3. Enter the term in years: the original term, or the remaining term if you entered a remaining balance.
4. Enter the extra monthly amount: the amount you will add every month on top of the scheduled payment. The worked example uses $200.
5. Add a first payment date only if you want calendar payoff dates: with a date entered, the results show a month and year as well as a payment count. Without one, they show payment counts only.
6. Click Calculate: the results box shows both payments, both payoff points, time saved, both interest totals, interest saved, a one-line interpretation, and the year-by-year table. Copy or share the result with the buttons in the results box.

Invalid inputs are rejected with an inline message and no results are shown: a blank or non-positive loan amount, a blank or negative rate, a blank or non-positive term, or a negative extra payment. A blank extra payment is treated as $0, which shows the standard loan with no saving.

The formula: standard payment, then month-by-month simulation

The standard payment comes from the amortization formula, where P is the loan amount, r is the monthly rate (annual rate divided by 12), and n is the total number of payments.

The simulation matters because a single multiplication cannot price an early payoff. Multiplying extra by 12 by the number of years overstates what you pay, since the loan ends early and the later years never happen. Simulating month by month, with the final payment trimmed to the exact remaining balance, is the only method that gives the true interest total and the true payoff month. The mortgage payment calculator covers the standard payment on its own if you only need that figure, and the remaining mortgage balance calculator gives the balance at any point for a loan you already hold.

Worked example: $300,000 at 6.5% over 30 years

The pre-filled values are a $300,000 loan, 6.5% fixed, 30 years, and $200 extra per month, with no start date. Running them gives a standard payment of $1,896.20 and a payment with extra of $2,096.20. The standard loan runs 360 payments with $382,633.47 of interest. With extra it runs 277 payments with $279,184.67 of interest. The saving is 83 payments, which is 6 years 11 months, and $103,448.79 of interest, which is 27.0% of the standard interest total.

The size of the extra payment changes the prize faster than most people expect, because each extra dollar also kills the interest that dollar would have carried for the rest of the loan. The table below runs the same $300,000 loan at 6.5% over 30 years at five extra amounts. Every row is a real run of the tool.

The first $100 buys $60,994.79 of saving. The next $100 buys $42,454.00 more. Returns diminish as the extra grows, because a loan that is already short has fewer future interest months left to kill. That is the honest shape of the trade, and it is why the tool shows the full table rather than a single headline number.

Monthly extra, lump sum, or biweekly: timing is the whole story

Money paid earlier saves more than the same money paid later, because it stops interest sooner. A lump sum paid in January beats the same total spread across the year in monthly pieces, and monthly pieces beat the same total paid as one lump sum in December. The pay off loan early calculator covers the general early-payoff case for other loan types, while the loan additional payment calculator models extra payments on a generic loan rather than a mortgage. If your servicer offers a biweekly plan, check what it actually does: a true biweekly plan collects half a monthly payment every two weeks, which adds up to 26 half payments, or 13 monthly payments, per year. That thirteenth payment is the saving, not the frequency itself, and you can reproduce it here by dividing one monthly payment by 12 and entering that as the extra amount.

What competing calculators miss

Extra-payment tools divide into a few camps, and each leaves something out:

• Remaining-term tools (Bankrate’s additional payment calculator): strong for borrowers already partway through a loan, because they ask for years remaining and the original term. What they do not give you is the year-by-year balance comparison that shows the gap compounding, and they frame the answer around an existing loan rather than a new one.
• Multi-mode payoff tools (Calculator.net’s mortgage payoff calculator): the broadest option set, with monthly extra, yearly extra, one-time payments, biweekly schedules, and a remaining-term mode. The breadth is real, but the output is a single payoff summary plus a full amortization table, not a compact side-by-side yearly comparison of the two balances.
• Full-payment tools with PITI and PMI: useful if you want the total monthly housing cost, including taxes, insurance, and private mortgage insurance. They answer a different question: what leaves your bank account each month, not how fast principal falls. Mixing escrow into a principal simulation muddies both answers.
• The gap this tool fills: a clean principal-and-interest simulation with an honest 0% rate path, a calendar payoff date when you supply a start date, and a year-by-year table that keeps both balances visible until the standard term ends, so you can see exactly when the extra-payment loan disappears.

Before you send extra principal: three checks

First, confirm the extra is applied to principal. The Consumer Financial Protection Bureau’s guidance on prepayment penalties notes that penalties do not normally apply to small extra principal payments made in chunks, but it also says to double-check with the lender, and some servicers treat an unlabelled extra payment as an advance on next month’s bill instead. Write “principal only” on the payment or set the instruction in the servicer’s portal, then verify on the next statement that the balance fell by the full extra amount.

Second, check for a prepayment penalty in your note. Most modern US residential mortgages carry none, and federal rules cap any penalty that does exist to the first three years of the loan, at 2% of the outstanding balance in the first two years and 1% in the third. A penalty that applies only to a full payoff or a large lump sum may never touch small monthly extras, but the only safe source is your own note.

Third, weigh the guaranteed return against your other uses for the cash. Paying extra earns a guaranteed return equal to your mortgage rate, before tax effects. Investing might earn more, but with risk and no guarantee, and an emergency fund or high-interest debt usually comes first. This tool shows the mortgage side of that decision; it is not financial advice, and a housing counselor can walk through the full picture for free.

One more honest limit: the tool assumes the rate never changes and the payment never changes. An adjustable-rate loan, a loan with a balloon payment, or a loan where the scheduled payment is recast will diverge from the simulation. The mortgage accelerator calculator takes a different angle on shortening a mortgage if you want a second view on the same goal.

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