A mortgage extra payment calculator compares the regular amortization with a schedule that applies more money to principal. It can model an increase on every payment, an annual lump sum, a separate one-time lump sum, or a combination of the three.
The calculation shows a potential interest saving and earlier payoff, but the mortgage contract decides whether the payment is allowed without a charge. Check the amount, timing, notice, and annual reset rules before acting.
Choose the prepayment pattern you can sustain
Use extra-per-payment for a recurring increase tied to every regular payment. Use annual lump sum for a repeatable once-a-year amount. Use one-time lump sum when modeling a tax refund, bonus, inheritance, sale proceeds, or other single principal reduction at a chosen future payment.
Keep the base mortgage assumptions identical when comparing strategies. If the rate, amortization, or frequency also changes, you will not know how much of the difference came from the prepayment itself.
Interpret interest saved and time saved
Interest saved is the difference between the base schedule's total interest and the accelerated schedule's total interest under the same rate assumption. Time saved compares the modeled payoff dates. The result will change at renewal if the interest rate or payment changes.
A prepayment is not automatically the best use of cash. Compare the guaranteed mortgage interest avoided with emergency reserves, higher-interest debt, tax considerations, and the uncertain return from other uses of the money.
Check the contract before paying extra
The Financial Consumer Agency of Canada advises borrowers to check the mortgage contract for the permitted lump-sum amount and dates. Paying more than the privilege allows can trigger a prepayment penalty. Some lenders also limit payment increases or define when an annual privilege resets.
Ask the lender to confirm in writing how the payment will be applied and whether notice is required. After it posts, compare the new balance with the calculator and keep the lender statement with your plan.
Compare the prepayment with other uses of cash
Run a conservative case with no future lump sums, a sustainable recurring increase, and the largest one-time amount you are seriously considering. This shows the range of interest and payoff outcomes without assuming that every future bonus or refund will be available.
Keep enough liquidity for repairs, income disruption, and other priorities. A calculator can measure avoided mortgage interest, but it cannot value flexibility or decide whether higher-interest debt, employer matching, or another goal should come first.
Frequently asked questions
Can I calculate one extra mortgage payment?
Yes. Enter the amount as a one-time lump sum and select the payment number at which it will reduce principal.
Do extra payments always save interest?
A valid principal prepayment normally reduces later interest, but penalties or lost liquidity can change the broader financial outcome.
Is accelerated biweekly the same as regular biweekly?
No. Accelerated biweekly commonly pays half the monthly amount every two weeks, which creates the equivalent of one additional monthly payment each year.
Sources and further reading
Mortgage rules and market data can change. Follow the links for current official information.