Extra Mortgage Payment Calculator

Enter any extra monthly payment — see your new payoff date, total interest saved, and a side-by-side amortization comparison against your current schedule.

How Extra Principal Payments Work

  • Every dollar of extra principal you pay reduces your loan balance immediately — and that lower balance is what future interest is calculated on. The effect compounds over time, so extra payments made early in the loan save the most.
  • Even a small extra payment can have a dramatic impact on a long-term mortgage. An extra $200/month on a 30-year $300k loan at 6.5% can save over $80,000 in interest and cut roughly 6 years off the payoff.
  • Unlike refinancing, making extra payments has no closing costs, no new loan qualification, and no rate risk. It's the simplest way to accelerate payoff on any existing mortgage.

Calculation details

Methodology

The baseline and extra-payment scenarios use the same fixed monthly P&I payment. Each month, interest is calculated from the remaining balance, scheduled principal is applied, and the entered extra amount is added directly to principal. The schedules stop when the balance reaches zero.

Assumptions and limitations

  • Extra payments are applied to principal immediately every month.
  • The scheduled payment is not recast after principal reductions.
  • Payment rounding, escrow, fees, prepayment penalties, and opportunity cost are excluded.
  • The rate remains fixed and the loan is not refinanced or modified.
  • Borrowers should give their servicer instructions for applying extra principal.

Worked example: $200 extra each month

  • $300,000 loan
  • 6.5% fixed rate
  • 30-year term
  • $200 extra principal every month

The standard P&I payment is about $1,896. Paying about $2,096 total finishes the modeled loan in 277 months instead of 360 and saves about $103,449 in interest.

The model shortens payoff by about 83 months. Actual savings depend on the servicer applying the extra amount to principal as intended.

Official sources

Frequently Asked Questions

What happens when I make extra mortgage payments?

Extra principal payments reduce your outstanding loan balance immediately. Because your next month's interest charge is calculated on that lower balance, less of each future payment goes to interest — and more goes to principal. This snowballs over time: each extra payment makes subsequent extra payments even more effective.

Is it better to make extra mortgage payments or invest the money?

It depends on your mortgage rate vs. expected investment returns. If your mortgage rate is 7% and the market historically returns 8%–10%, investing may come out ahead mathematically — but comes with volatility risk. Paying down the mortgage is a guaranteed 7% after-tax return with zero risk. Many financial advisors suggest doing both: fund retirement accounts first (especially if your employer matches), then apply extra cash to the mortgage.

Do extra mortgage payments go to principal or interest?

Extra payments should always be designated as 'applied to principal.' Check your lender's payment portal to confirm this — some servicers apply extra funds to the next month's payment by default rather than reducing principal. Call your servicer or submit a written instruction if needed. Confirm on your next statement that your balance decreased by the extra amount.

How early in the loan should I make extra payments for maximum savings?

As early as possible. Extra payments made in year 1 save more than those made in year 20 because the loan balance is higher, so more future interest gets eliminated. However, extra payments always save money regardless of when you make them — the interest you avoid paying is always greater than zero. Even 10 years into a 30-year mortgage, extra payments can save $20,000–$40,000.

How to use this estimate

This calculator is an educational planning tool. Results are based on the figures and assumptions entered by the reader, use standard mortgage mathematics, and are not a loan offer, approval, or substitute for a lender's Loan Estimate. Taxes, insurance, fees, mortgage insurance, and available rates vary by borrower, property, lender, and location.

Review the assumptions, compare more than one scenario, and confirm the final numbers with a licensed mortgage professional before making a financial commitment.