How to use the mortgage payoff calculator
- Enter your Remaining balance — what you still owe today, not the original loan.
- Enter the Interest rate and the Remaining term in months.
- Set the Extra each month you could comfortably add.
- Read the interest saved and the time cut off the end of the loan.
Worked example
A $250,000 balance at 6.5% with 300 months left costs roughly $1,688 a month. Adding $200 a month clears the loan about 5 years 6 months early and removes roughly $65,000 of interest — the exact figures appear above.
Why extra payments hit so hard
A mortgage payment splits into interest and principal. The interest is charged on whatever balance remains, so an extra payment today removes principal that would otherwise have been charged interest every month until the end of the term.
Monthly interest = Balance × (Annual rate ÷ 12)
New balance = Balance + Interest − Payment
Early in a mortgage most of the payment is interest, which is why extra payments made in the first years are worth far more than the same amount paid near the end. On a 6.5% loan, every $100 of principal removed in year two saves around $200 of future interest over a 25-year term.
Where to send the money
Most lenders let you choose whether an extra payment reduces the balance or the term. Reducing the balance lowers the monthly payment; reducing the term keeps the payment but finishes earlier and saves more interest. If your goal is the smallest total cost, ask for the term option.
Before you overpay, check these
- Prepayment penalty. Some fixed-rate loans charge a fee for early repayment. Ask first — the penalty can outweigh a year of savings.
- Emergency fund. Money sent to the mortgage is hard to get back. Keep three to six months of expenses liquid before overpaying.
- Higher-rate debt first. A credit card at 20% costs more than a mortgage at 6.5%. Clear the expensive debt, then overpay.
- Tax deduction. If you itemise mortgage interest, the effective saving is smaller than the raw figure. Compare after-tax numbers.
- Investing alternative. If your expected after-tax investment return beats the mortgage rate, investing the extra may come out ahead — but it carries risk that repaying debt does not.
Making it automatic
Rounding the payment up to the next hundred and setting it as a standing order turns the plan into a habit. Even an extra $50 a month compounds: it is the direction of travel, not the size of the step, that decides when the loan ends.