How this extra mortgage payment calculator works
The calculator builds a current payoff schedule from the loan balance, interest rate and monthly payment. It then builds a second schedule with the extra monthly payment and any one-off payment entered.
How extra payments can reduce interest
If extra payments are applied to principal, the balance falls sooner. A lower balance can reduce future interest, which may shorten the estimated payoff time.
Current schedule vs extra-payment schedule
The comparison shows the estimated payoff time, payoff date, total interest and total paid for both schedules. Remaining term is used as a sense check, but the schedule is calculated from balance, rate and payment.
Why lender payment rules matter
Some lenders apply extra payments differently or require instructions for principal-only payments. Actual payoff quotes can also differ because of daily interest, fees and timing.
What this calculator does not include
This calculator does not include prepayment penalties, tax effects, lender-specific allocation rules, offset or redraw accounts, refinance decisions, daily interest or official payoff quotes.
Key terms and assumptionsFormula notes, key terms, source assumptions and limits used in this calculator.
These notes are specific to this calculator. Read the property methodology notes for shared property formulas, region settings and estimate limits.
- Principal application
- Extra payments are assumed to reduce principal after monthly interest is applied.
- Current schedule
- The current payoff schedule is calculated from balance, interest rate and monthly payment.
- One-off payment
- A one-off payment is applied in the month entered and capped to the remaining balance.
- Payoff date
- The payoff date label uses the start month and year entered. It is an estimate, not an official payoff quote.
- Lender rules
- Actual results can differ if a lender applies extra payments differently or charges fees.
- Region settings
- Region settings change defaults, labels and currency formatting only. They do not convert exchange rates or create country-specific results.
- General estimate
- The calculator excludes tax effects, prepayment penalties, offset accounts, redraw features and lender-specific payoff rules.
Guides and methodology
Plain-English notes that explain the assumptions behind related calculators and tools.
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FAQs
How do extra mortgage payments save interest?
If applied to principal, extra payments reduce the balance that future interest is charged on.
Can I use this as an extra repayments or overpayment calculator?
Yes. Extra repayments, overpayments and extra mortgage payments are treated as additional amounts applied to the loan balance under the assumptions entered.
Does this assume extra payments go to principal?
Yes. The estimate assumes extra amounts are applied to principal after monthly interest.
What if my lender applies payments differently?
Your actual result may differ. Check lender rules and payoff statements.
Can I include a one-off extra payment?
Yes. Use the advanced one-off payment field and choose the payment month.
What if my current payment does not cover interest?
The calculator will warn that the loan would not pay down under those assumptions.
Does this include prepayment penalties?
No. It does not include penalties, fees, tax effects, offset accounts or redraw features.
Why does the entered remaining term matter?
It helps explain the current schedule, but the payoff estimate is based on balance, rate and payment.
Can I use this outside the United States?
Yes. Region settings change defaults, labels and currency formatting only. They do not perform exchange-rate conversion.