How extra payments compound against your principal
Every dollar you pay above your scheduled monthly payment reduces your loan's principal balance — and that reduction compounds because every future interest charge is calculated on a smaller balance. The effect is dramatic: a $300/month overpayment on a $280,000, 30-year, 6.5% mortgage saves roughly $86,000 in interest and pays off the loan about 7 years early.
Three strategies compared
- Fixed monthly overpayment — The most flexible strategy. You commit a fixed additional amount to principal each month, and you can stop or adjust if circumstances change.
- Biweekly payments — You pay half your monthly payment every two weeks. Because there are 26 biweekly periods in a year, you make one extra monthly payment per year with minimal monthly cash-flow impact.
- One-time lump sum — Best for bonus-driven cash flow or windfalls (inheritance, sale of asset). The lump sum immediately reduces principal and compounds for the remaining life of the loan.
The opportunity cost question
Before accelerating mortgage payoff, compare your mortgage rate to the after-tax return you could earn by investing the same dollars. If your mortgage rate is 6.5% and your expected after-tax investment return is 7%, investing mathematically wins over the long run — but the certainty of a paid-off home has psychological value that pure math cannot capture.
For a deeper comparison of payoff strategies, including recasting vs refinancing, see our mortgage payoff strategy guide.