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How Extra Payments Shorten a Mortgage
Every extra dollar goes straight to principal, and interest is charged only on remaining principal. The calculator runs your full amortization schedule month by month — standard formula M = P·[i(1+i)^n]/[(1+i)^n−1] — then re-runs it with your extra payment applied, showing exactly how much interest you save and how many months you cut.
Extra Monthly vs Lumpsum vs Biweekly
An extra monthly amount compounds steadily. A one-time lumpsum early in the loan saves the most per dollar, because early payments face the most future interest. Biweekly payments — half your payment every two weeks — sneak in one full extra payment per year. The tool models all three so you can compare against your actual budget.
When Prepaying Makes Sense
Extra principal can shorten the loan and reduce future contractual interest when the lender or loan servicer applies it to principal. The net benefit can differ after applicable tax treatment or charges, and cash moved into home equity becomes less liquid. Check for prepayment penalties in your loan terms, and keep your emergency fund intact before committing extra cash.
Reading Your Results
The output shows total interest saved, months eliminated, and your new payoff date, with a chart comparing both balance curves. Small changes compound: even $100 extra per month on a typical 30-year loan commonly saves tens of thousands in interest.
Why Early Extra Payments Save More Than Later Ones
A mortgage's amortization schedule charges interest only on the remaining principal each month, and in the early years that principal is at its highest — so a dollar applied to principal in year 2 eliminates far more future interest than the same dollar applied in year 25, when the balance is already small. This is why a lump sum right after closing outperforms the same lump sum applied later, and why even a modest recurring extra payment started early compounds into large total savings over a 30-year term.
Biweekly Payments: One Sneaky Extra Payment a Year
Splitting a monthly payment into two half-payments every two weeks produces 26 half-payments a year — the equivalent of 13 full monthly payments instead of 12, because a year has slightly more than 52 weeks. That extra payment goes straight to principal the same way a manual lump sum would, without requiring the discipline of remembering to send extra money each month. The catch is administrative, not mathematical: confirm your loan servicer applies each half-payment immediately rather than holding it until a full payment accumulates, since some do the latter and erase the benefit.
Avoided Interest vs Opportunity Cost — Framing the Prepay-or-Invest Decision
Every extra dollar applied to principal reduces the balance on which future interest is calculated. That saving follows the loan terms, but its net value after applicable tax treatment or charges need not equal the headline rate, and the added home equity is less liquid. The counter-argument is opportunity cost: money locked into home equity can't compound in the market instead, and historically diversified equity returns have exceeded typical mortgage rates over long horizons, though never without risk and volatility along the way. There's no universally correct answer, which is why the calculator models both the mortgage-payoff path and leaves the market comparison to the borrower's own risk tolerance and timeline.
Frequently asked questions
How much does paying an extra $200 a month save on a mortgage?
On a $350,000 loan at 6.5% for 30 years, an extra $200/month saves roughly $100,000 in interest and pays the loan off about 6 years early. The exact savings depend on your balance, rate, and how early you start — extra payments in the first years save the most. Enter your own numbers above for a precise figure.
Do biweekly mortgage payments really save money?
Yes — paying half your monthly payment every two weeks results in 26 half-payments (13 full payments) per year instead of 12. That one extra annual payment goes straight to principal, typically cutting 4–6 years and tens of thousands in interest from a 30-year loan. Confirm your lender credits biweekly payments properly rather than holding them until month-end.
Is it better to pay a lump sum or extra monthly payments?
Dollar for dollar, money applied earlier saves more interest, so a lump sum today beats the same total spread over future months. But a recurring extra payment compounds its effect every month for the life of the loan. Use the calculator to test both against your actual loan — the gap is often smaller than expected.
Should I pay off my mortgage early or invest instead?
Extra principal can shorten the loan and reduce future interest, but the net benefit depends on applicable tax treatment, any prepayment charge, liquidity needs, and the uncertain after-tax return of alternatives. Check the loan terms and make sure the lender or loan servicer applies the extra amount to principal.
Do extra mortgage payments have penalties?
Most US conforming loans (Fannie Mae/Freddie Mac) originated after January 2014 cannot charge prepayment penalties. Some non-qualified, jumbo, or older loans still can, typically only in the first 3 years. Check your loan estimate or ask your servicer, and always specify that extra payments go to principal.