How much can an extra $100 mortgage payment save?
For a new $300,000, 30-year mortgage at a fixed 6.5% rate, adding $100 to principal every month from the first payment saves approximately $60,995 in interest and pays off the loan in 312 months instead of 360. This monthly model excludes taxes, insurance, fees, and penalties. Your loan balance, rate, payment timing, and servicer’s rules change the result.
Below: the calculation method, a comparison of three extra-payment amounts, and the Roof & Ratio calculator for trying your own assumptions.
Try the example with your own assumptions using our free MyLoanTable amortization calculator with extra payments. No signup is required, and you can print or download the schedule.
You make the payment every month, but your mortgage balance seems to move slowly. An amortization schedule shows why: each payment is divided between interest and the principal you still owe.
A mortgage amortization calculator with extra payments lets you compare the regular schedule with a different plan. You can see how additional principal changes the interest cost and payoff time before deciding what fits your budget.
How mortgage amortization works
For a standard fully amortizing fixed-rate mortgage, the scheduled principal-and-interest payment stays level. The interest portion generally falls as the balance declines, leaving more of each payment to reduce principal. Your total housing payment can still change if taxes, insurance, or other charges change.
In a monthly model, interest for the month = beginning loan balance × annual interest rate ÷ 12. Subtract that interest from the scheduled principal-and-interest payment to find the principal paid.
A $300,000 mortgage example
Assume a new $300,000 mortgage with a fixed 6.5% annual interest rate, a 30-year term, and payments made monthly. The calculated principal-and-interest payment is approximately $1,896.20.
- First-month interest: $300,000 × 6.5% ÷ 12 = $1,625.
- First-month principal: approximately $271.20.
- Total scheduled interest over 360 payments: approximately $382,633.
These figures exclude taxes, insurance, PMI, HOA dues, loan fees, and penalties. The interest rate is an illustrative assumption, not a current rate quote.
What an extra $100, $200, or $300 can change
The following calculation assumes the same loan and an extra principal payment made with every monthly payment, starting with the first payment. It keeps the regular principal-and-interest payment unchanged, reduces the final payment to the amount still due, and uses unrounded internal calculations.
| Extra principal each month | Payments to payoff | Estimated interest saved |
|---|---|---|
| $0 | 360 months · 30 years | $0 |
| $100 | 312 months · 26 years | $60,995 |
| $200 | 277 months · 23 years, 1 month | $103,449 |
| $300 | 250 months · 20 years, 10 months | $135,115 |
For this example, an extra $100 a month shortens repayment by about four years. Starting later, using a different interest rate, or making irregular extra payments changes the savings. Servicer rounding and payment timing can also produce small differences.
Use the mortgage amortization calculator with extra payments
The Roof & Ratio Mortgage Amortization & Extra Payment Calculator compares regular and accelerated payoff schedules, separates principal and interest, and displays an interactive loan-balance chart. It includes monthly and yearly schedules, a printable view, and CSV export.
- Enter the loan amount, annual interest rate, term, and timing requested by the calculator.
- Review the regular payment and the principal-versus-interest breakdown.
- Try an extra monthly principal amount that fits your budget and compare the results.
- Print the schedule, save a PDF through your browser, or export the CSV.
If you are already partway through a loan, use inputs that reflect your current balance and remaining repayment period when modeling from today. Compare the modeled payment with your statement; a difference means the assumptions need review.
The paid tool is a downloadable interactive HTML file that opens in a modern browser on a phone, tablet, or computer. It does not require Excel or Google Sheets. See the calculator’s features and preview.
Check how your servicer applies extra payments
Ask your servicer how to designate an additional payment toward principal and confirm its application on your statement. Review your loan terms for prepayment restrictions or penalties. The CFPB explains that small extra principal payments do not normally trigger prepayment penalties, but borrowers should check with their lender.
Extra principal generally shortens the repayment timeline in this model; it does not automatically lower your required monthly payment. Consider your cash reserve and other financial obligations before committing money you may need soon. Your loan servicer or financial professional can help evaluate your circumstances.
Connect the payment to your full property budget
Keep taxes, insurance, PMI, HOA fees, maintenance, and other costs in your housing budget even though they are separate from principal and interest. If the property is a rental, use our rental property cash flow guide to see how debt service fits with rent and operating expenses.
For additional background, see the CFPB’s mortgage servicing guidance.
By Marchelle Cook. Educational planning information only; not individualized financial, tax, or lending advice. Figures are estimates for the stated assumptions.
Common extra-payment questions
Will extra principal lower my required monthly payment?
In the fixed-payment model used here, extra principal shortens repayment. It does not automatically reduce the required monthly payment. Ask your servicer about its rules if your goal is a lower required payment.
Is the 6.5% example a current mortgage offer?
No. It is a fixed illustrative assumption so you can follow the arithmetic. Enter your own loan’s rate and balance when comparing scenarios.
Can I open the calculator in Excel?
The working calculator is a downloadable HTML file that opens in a modern browser. Its exported CSV schedule can be opened in compatible spreadsheet software.