How this calculator works
This calculator compares standard mortgage amortization with an accelerated schedule when you add a fixed extra payment every month. Enter remaining loan balance, annual interest rate, remaining term in years, and extra monthly payment amount.
The standard path uses the regular monthly payment computed from balance, rate, and term, paying down principal over the full remaining schedule. The accelerated path applies the same base payment plus your extra amount each month, with extras directed to principal after interest is satisfied.
Outputs include interest saved, standard monthly payment, standard payoff time in months, accelerated payoff time, and months saved. Interest saved equals total interest on the standard schedule minus total interest on the accelerated schedule.
The model assumes extra payments apply to principal consistently, no prepayment penalties, and no changes to rate or escrow. It focuses on principal and interest only—not property tax, insurance, or HOA.
What affects the result
Four inputs drive the comparison. Extra payments matter most on longer terms and higher rates because more interest accrues over time.
- Remaining loan balance is what you owe today. Larger balances produce larger absolute interest savings from the same extra payment.
- Interest rate sets monthly interest charges. Higher rates mean more of each standard payment goes to interest, so principal-reducing extras often save more.
- Remaining term affects how many months interest can accrue. Longer remaining terms amplify savings from early principal reduction.
- Extra monthly payment is the additional amount beyond the required payment. Even $100 to $200 per month on a 30-year loan often saves tens of thousands in interest and cuts years off the term.
Early in a loan, a larger share of each payment is interest. Extras during those years reduce balance faster and compound savings over remaining months.
Real-world examples
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$320,000 balance at 6.5% with 30 years left, $200 extra. Standard payment near $2,022; $200 extra may save roughly $80,000+ in interest and shorten payoff by several years depending on exact amortization—run your numbers for precise results.
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15 years remaining on a lower-rate loan. A 3.5% rate produces less interest overall, so extras save fewer dollars than the same extra on a 6.5% loan—but freeing cash flow sooner may still be worthwhile.
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Zero extra baseline. Enter $0 extra to see standard payoff timeline and interest, then increment extras in $50 steps to find a sustainable amount with meaningful savings.
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Comparing to refinance. If refinance lowers rate from 7% to 6%, interest savings apply to the whole balance. Extras attack principal on your current loan. Use the refinance break-even calculator alongside this tool when both options are on the table.
Common mistakes
- Using original loan amount instead of current balance. Enter today's remaining balance from your statement.
- Using original 30-year term when 22 years remain. Remaining term must reflect time left, not initial term.
- Assuming prepayment without confirming servicer application. Ensure extras apply to principal, not next month's bill.
- Ignoring prepayment penalties on older loans. Rare on modern mortgages but possible.
- Prioritizing mortgage prepayment while carrying high-rate credit card debt. Avalanche logic often favors cards first.
- Draining emergency savings for extras. Maintain liquidity before aggressive prepayment.
When to use this calculator
Use this calculator when you have cash flow for consistent extra payments and want to quantify interest savings and earlier payoff. It fits evaluating raises, bonuses applied monthly, or budget cuts redirected to the mortgage.
Read the pay off mortgage or car loan early guide for when prepayment beats investing or other goals. Pair with understanding amortization to see why early payments are interest-heavy. Use the loan payment calculator when estimating payments on a new loan rather than prepaying an existing one.
Frequently asked questions
Does every mortgage allow extra principal payments without penalty? Most mortgages originated since 2014 cannot carry prepayment penalties under Consumer Financial Protection Bureau qualified mortgage rules. Older loans, some portfolio loans, and certain state-specific products may still include them. Check your loan agreement or call your servicer before making large extra payments if your mortgage predates 2014 or is a non-standard product. For most standard 15- or 30-year fixed mortgages today, prepayment is unrestricted.
How do I make sure extra payments actually reduce principal? Contact your servicer or log into your loan portal before your first extra payment. Some servicers automatically apply extra funds to your next billing cycle rather than current principal, which delays the benefit. Look for an option labeled "apply to principal" when making online payments, or include a written note on paper checks. Confirm in your next statement that the principal balance fell by the expected extra amount.
Is it better to make extra payments monthly or make one large annual lump sum? Both reduce total interest compared to the standard schedule, but timing matters. Monthly extra payments reduce the principal balance sooner, so interest accrues on a lower balance throughout the year. An annual lump sum applied at the start of the year produces a larger one-time reduction. Monthly extras are often easier to budget consistently, while annual prepayments may work better when income is variable or bonus-based.
Should I pay extra on my mortgage or invest the money instead? Compare your mortgage interest rate to your expected after-tax investment return. At higher mortgage rates — above 6% to 7% — extra payments offer a guaranteed return equal to the rate, often competitive with stock returns adjusted for risk and taxes. At lower legacy rates below 4%, long-term investment returns have historically exceeded the guaranteed mortgage savings. There is no universal answer — also consider your emergency fund, high-rate debt, and risk tolerance. Read the pay off mortgage or car loan early guide for a fuller framework.
Does refinancing make more sense than extra payments? Refinancing lowers the rate on your entire remaining balance, reducing every future payment from that point forward. Extra payments attack principal at your current rate. If available refinance rates are meaningfully lower than your rate, calculate the break-even first with the refinance break-even calculator — a rate drop can save more than extra payments on the higher original rate. If rates are similar or higher than your existing rate, extra payments on your current loan are the better lever to pull.
How much earlier would I pay off a 30-year mortgage with $200 extra per month? The exact answer depends on your balance, rate, and remaining term, but on a typical 30-year loan at 6.5% to 7%, an extra $200 per month often shortens payoff by four to six years and saves $50,000 to $100,000 or more in interest. Run the calculator with your actual balance and rate for the precise impact — even $100 per month produces meaningful results on longer remaining terms.
Related calculators
Estimate your base mortgage principal and interest payment on any loan amount with the loan payment calculator. Compare whether refinancing to a lower rate saves more than prepaying your current loan with the refinance break-even calculator. Check overall housing budget and maximum purchase price with the home affordability calculator. Review how monthly debts affect mortgage qualification with the debt-to-income calculator. Model auto loan prepayment using the same extra-payment logic for a car with the auto loan calculator.
FAQ
How do extra mortgage payments save interest?
Each month, your standard payment covers interest first, then principal. An extra payment applied to principal reduces the balance that future interest accrues on. Because interest is calculated on remaining balance, even modest extras compound into meaningful savings over a 15- or 30-year loan.
Should extra payments go to principal?
Yes. Confirm with your servicer that additional amounts apply to principal and do not prepay next month's payment unless that is your intent. Some lenders require a note or online selection. Principal-directed extras shorten the loan; misapplied payments may not produce the same benefit.
Is paying off a mortgage early always the best use of money?
Not always. Compare your mortgage rate to after-tax returns on investments, emergency fund needs, and higher-rate debt. The pay-off-mortgage-or-car-loan-early guide walks through when accelerated payoff beats alternatives. This calculator quantifies mortgage savings only—it does not rank against other goals.
What if I make one lump sum instead of monthly extras?
Use advanced options to enter an annual lump sum or a one-time extra payment in a specific month. Lump sums reduce principal immediately; monthly extras reduce balance sooner throughout the year. Both shorten payoff and save interest compared with the standard schedule.
Does this include escrow, taxes, or insurance?
No. It focuses on principal and interest on the loan balance you enter. Property taxes, insurance, and HOA are separate housing costs. Extra payments typically apply to loan principal, not escrow buckets, unless your servicer handles them differently.
How much can a small extra payment save?
On a 30-year mortgage, even $100 to $200 per month often saves tens of thousands in interest and cuts years off the term. Run the calculator with and without your planned extra to see months saved and interest avoided for your specific balance and rate.
Will my lender charge a prepayment penalty?
Most modern residential mortgages have no prepayment penalty, but some older or non-standard loans do. Check your note before committing to aggressive prepayment. A penalty could offset part of the interest savings this calculator estimates.
Should I refinance instead of making extra payments?
Refinancing to a lower rate reduces interest on the entire balance; extra payments attack principal on your current loan. If rates dropped materially, compare refinance break-even against extra payment savings. Sometimes both strategies together make sense over time.
What inputs should I use for remaining term?
Enter years left on your loan, not the original 30-year term if you are several years in. Use current remaining balance from your statement, not original loan amount. Accurate inputs produce realistic payoff comparisons.
How is this different from the loan payment calculator?
The loan payment calculator computes monthly payment from loan amount, rate, and term. This calculator starts from an existing loan and compares standard payoff with an accelerated schedule when you add a fixed extra each month. Use loan payment for new borrowing; use this tool for prepayment planning.