See how an extra monthly payment shortens your loan.
n_new = −ln(1 − (r × P₀) / (M + E)) / ln(1 + r)
To find the new number of months to pay off the mortgage when making extra payments, we use the standard amortization payoff-period formula but substitute P + E (regular payment plus extra payment) for the payment amount:
First, calculate the standard monthly payment (if not already known):
M = P₀ × [r(1+r)ⁿ] / [(1+r)ⁿ − 1]
Then calculate the new number of months to payoff using the extra-payment amount:
n_new = −ln(1 − (r × P₀) / (M + E)) / ln(1 + r)
The interest saved is:
Savings = (M × n) − ((M + E) × n_new)
All calculations assume a fixed interest rate and that extra payments are applied directly to the principal.
Step 1 – Calculate required monthly payment M: M = 250,000 × [0.005 × (1.005)^360] / [(1.005)^360 − 1] (1.005)^360 ≈ 6.02258 M = 250,000 × [0.005 × 6.02258] / [6.02258 − 1] M = 250,000 × 0.030113 / 5.02258 M = 250,000 × 0.005996 ≈ $1,498.88 Step 2 – Calculate new payoff period with E = $200: n_new = −ln(1 − (0.005 × 250,000) / (1,498.88 + 200)) / ln(1.005) = −ln(1 − 1,250 / 1,698.88) / ln(1.005) = −ln(1 − 0.73578) / 0.0049875 = −ln(0.26422) / 0.0049875 = −(−1.33076) / 0.0049875 = 1.33076 / 0.0049875 ≈ 266.8 months → 267 months Step 3 – Calculate interest saved: Original total paid = $1,498.88 × 360 = $539,596.80 New total paid = $1,698.88 × 267 = $453,601.96 Savings = $539,596.80 − $453,601.96 ≈ $85,995
Result: New payoff time: ~267 months (22 years, 3 months) instead of 360 months (30 years). Time saved: ~93 months (7 years, 9 months). Total interest saved: approximately $85,995.
By adding just $200 per month to a $250,000 mortgage at 6%, you would pay off the loan nearly 8 years early and save roughly $86,000 in interest. The earlier in the loan term you start making extra payments, the greater your savings — because more of your early payments would otherwise go toward interest rather than principal. Results are estimates and may differ from your actual lender statement due to escrow, PMI, rounding conventions, or rate adjustments on variable-rate loans.
Every mortgage payment you make consists of two parts: interest and principal. In the early years of a 30-year mortgage, the vast majority of each payment goes toward interest. This is called amortization — the gradual reduction of a loan through scheduled payments.
When you make an extra payment applied to principal, you reduce the balance on which future interest is calculated. That means your next month's interest charge is slightly lower, so more of your regular payment chips away at principal. This compounding effect snowballs over time, cutting years off your loan.
Not necessarily. Compare the guaranteed return of paying off a 6% mortgage (equivalent to a 6% after-tax return) against alternative uses of that money: investing in index funds, paying off higher-interest debt, or building an emergency fund. For many homeowners, a balanced approach — contributing extra to the mortgage while still investing — is optimal.
Note: This calculator provides estimates only. Actual payoff dates and interest savings may vary based on your lender's exact amortization schedule, escrow requirements, any applicable prepayment fees, and whether your loan has a variable rate.
On a $300,000 mortgage at 6%, you would pay approximately $347,515 in interest over 30 years but only about $155,683 over 15 years — a savings of roughly $191,832. The extra monthly payment needed to achieve this is about $878 on top of your standard payment.
Refinancing to a 15-year mortgage locks in a lower rate and a higher required payment, often saving more total interest. However, it removes flexibility — you must make the higher payment. Extra payments on a 30-year loan offer the same potential savings with the flexibility to stop if finances change.
No. Only the mortgage interest portion of your payments is potentially tax-deductible (subject to IRS limits and itemizing requirements). Principal payments, including extra ones, are not tax-deductible.
When you pay off your mortgage, your lender is required to close your escrow account and refund any remaining balance, typically within 20 business days under federal RESPA guidelines. You then become responsible for paying property taxes and homeowners insurance directly.
This is a personal finance decision. Paying off your mortgage offers a guaranteed, risk-free return equal to your interest rate. Investing historically returns more over long periods but carries market risk. Many advisors suggest paying off high-interest debt first, building an emergency fund, maximizing tax-advantaged retirement accounts, then considering extra mortgage payments.
It depends on your loan balance, interest rate, and remaining term. As a rough guide, on a $300,000, 30-year mortgage at 6.5%, paying roughly $350–$400 extra per month will cut about 5 years off your term. Use the calculator above with your specific numbers to get a precise answer.
No. This calculator models a consistent extra payment for simplicity. In practice, you can vary the amount — any extra principal payment helps. For irregular lump sums, recalculate after each extra payment using your updated balance.
Not always. You should explicitly instruct your lender (on the check memo or in your online payment portal) to apply the excess to principal. Without this instruction, some servicers apply it as a future payment, which does not save interest the same way.
Generally, no. On a standard fixed-rate mortgage, your required monthly payment stays the same even as you pay ahead. The payoff date moves closer, but your contractual payment amount does not decrease (unless you formally recast the loan).
This calculator assumes a fixed interest rate. For an ARM, results are only accurate for the fixed-rate period. After that, your rate — and therefore your savings — will change based on market conditions.
Biweekly payments (half your monthly payment every two weeks) result in 13 full monthly payments per year instead of 12, effectively adding one extra full payment annually. A dedicated extra monthly payment gives you more control over the amount and timing but achieves a similar goal of reducing principal faster.
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