NestMathMortgage Payoff Calculator
Enter your loan details and an extra monthly payment or lump sum to see the exact payoff date, months saved, and total interest avoided, with a year-by-year breakdown of the accelerated vs. standard repayment paths.
Parameters
Tax Advantage
In your first year, approximately $21,496 in mortgage interest may be tax-deductible. Accelerating payoff reduces this deduction over time as interest costs drop.
Time Saved
—
Add extra payments to see savings
Interest Saved
$0
Total Cost
$747,185
$747,185 without extra
Annual Interest Cost
Interest ViewInterest paid each year: standard schedule vs. accelerated payoff
A small lump sum now accelerates your payoff.
Mortgage interest compounds on your remaining balance. A single extra payment of $5,000 today eliminates far more than $5,000 in lifetime interest cost. Start with a lump sum, then layer in monthly extra payments to maximize savings.
If this helped you figure out your payoff strategy, ☕ a coffee seems fair.
| Year | Principal | Interest | Year-End Balance |
|---|---|---|---|
| 1 | $3,410 | $21,496 | $316,590 |
| 2 | $3,648 | $21,258 | $312,942 |
| 3 | $3,902 | $21,004 | $309,040 |
| 4 | $4,174 | $20,733 | $304,866 |
| 5 | $4,464 | $20,442 | $300,402 |
| 6 | $4,775 | $20,131 | $295,627 |
| 7 | $5,107 | $19,799 | $290,520 |
| 8 | $5,463 | $19,443 | $285,057 |
| 9 | $5,844 | $19,063 | $279,213 |
| 10 | $6,250 | $18,656 | $272,963 |
| 11 | $6,685 | $18,221 | $266,278 |
| 12 | $7,151 | $17,755 | $259,127 |
| 13 | $7,649 | $17,257 | $251,478 |
| 14 | $8,182 | $16,725 | $243,296 |
| 15 | $8,751 | $16,155 | $234,545 |
| 16 | $9,360 | $15,546 | $225,185 |
| 17 | $10,012 | $14,894 | $215,173 |
| 18 | $10,710 | $14,196 | $204,463 |
| 19 | $11,455 | $13,452 | $193,008 |
| 20 | $12,252 | $12,653 | $180,756 |
| 21 | $13,106 | $11,801 | $167,650 |
| 22 | $14,018 | $10,888 | $153,632 |
| 23 | $14,994 | $9,912 | $138,638 |
| 24 | $16,038 | $8,868 | $122,600 |
| 25 | $17,155 | $7,751 | $105,445 |
| 26 | $18,350 | $6,556 | $87,095 |
| 27 | $19,627 | $5,280 | $67,468 |
| 28 | $20,994 | $3,912 | $46,474 |
| 29 | $22,455 | $2,451 | $24,019 |
| 30 | $24,019 | $887 | — |
How the calculator works
The calculator runs two amortization schedules in parallel: your original loan as written, and an accelerated version with your extra payment added each month. For each monthly period, it applies the interest charge (balance × monthly rate), subtracts the total payment (standard + extra) from the balance, and repeats until the balance reaches zero. The month the accelerated balance hits zero is your new payoff date.
The optional lump-sum field applies a one-time principal reduction at the start of the loan. This immediately lowers the balance on which future interest is calculated. Because mortgage interest front-loads into the early years of a 30-year loan, an early lump sum has an outsized effect on total interest paid, more so than the same amount spread over many small extra payments later in the loan.
Both paths accumulate total interest paid, and the calculator shows the difference as "interest saved." The line chart plots remaining balance over time for both schedules. The point where the accelerated line hits zero is visually striking on longer loans, often cutting off years of the standard schedule.
Understanding your results
Months saved and interest saved are the two numbers that matter most. A 30-year mortgage at 6.75% on a $320,000 loan costs about $422,000 in total payments, including more than $100,000 in interest alone. Even modest extra payments chip away at that dramatically. The months-saved figure translates directly to months of your life where you're no longer writing a mortgage check, which has real value beyond the interest calculation.
The year-by-year table is useful for tracking equity milestones, particularly if you're planning to sell at a specific point and want to know your expected payoff versus market value. It also helps you see when the accelerated path crosses specific balance thresholds, like paying below the original purchase price or reaching 20% equity to cancel PMI.
Frequently asked questions
How much do extra mortgage payments actually save?
The savings depend on your loan balance, interest rate, and how early you start paying extra. On a $320,000 loan at 6.75%, an extra $200/month saves roughly $65,000 in interest and cuts about 5 years off the loan. The earlier in the loan term you make extra payments, the more impactful they are since more of your early payments go toward interest rather than principal.
Does paying extra principal reduce my monthly payment?
On a standard fixed-rate mortgage, paying extra principal does not reduce your required monthly payment it reduces your loan balance and therefore the number of payments remaining. Your scheduled monthly payment stays the same; you just pay off the loan sooner and skip the final months of payments. Some lenders offer loan recasting (reamortization) which can lower your payment for a fee, but that's a separate process.
Is it worth paying extra on my mortgage?
It depends on your other financial priorities. If you have high-interest debt (credit cards, personal loans), paying that off first almost always makes more sense than prepaying a 6–7% mortgage. If your only debt is the mortgage, prepaying gives you a guaranteed return equal to your interest rate. Compare that against your investment return expectations: if you expect 7%+ in the market and your mortgage rate is 6.5%, investing may produce better outcomes but prepaying the mortgage is risk-free.
How do I pay off my 30-year mortgage in 15 years?
The extra monthly payment required to halve a 30-year term is typically around 50–65% of your standard payment. On a $320,000 loan at 6.75%, the standard payment is about $2,076. To pay it off in 15 years you'd need to pay roughly $2,840/month an extra $764. The calculator shows the exact extra payment amount needed for any target payoff date.
What happens to a lump-sum payment applied at the start of a loan?
A lump sum applied at closing or early in the loan term reduces your principal balance from day one. All subsequent interest charges are calculated on the lower balance, so the savings compound throughout the remaining term. A $10,000 lump sum on a $320,000 loan at 6.75% saves approximately $23,000 in interest and shortens the term by about 18 months far more than applying the same $10,000 spread across many monthly extra payments later.
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