Mortgage Extra Payment Calculator
Use this mortgage extra payment calculator to see how much sooner you'd own your home — and the total interest you'd save — by paying extra principal each month. The same mortgage calculator with extra payments banks model.
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How this calculator works
An extra payment applied to principal compounds in your favor: every dollar paid early avoids years of interest charges. The math reuses the standard amortization formula with a higher monthly payment.
months_new = −log(1 − r × P / (PMT + extra)) / log(1 + r)
Real example: $350K at 6.5% with 29 years remaining. Adding $200/month to principal trims roughly 5.5 years off the term and saves ~$110,000 in total interest. Adding $500/month? About 11 years and ~$190K saved.
Source: Standard mortgage amortization formula. CFPB on extra payments — consumerfinance.gov mortgage tools.
FAQ
How much does an extra mortgage payment save?
On a $350K mortgage at 6.5% with 29 years remaining, adding $200/month to principal trims roughly 5.5 years off the term and saves ~$110,000 in total interest. Adding $500/month? ~11 years and ~$190K saved.
Should I prepay the mortgage or invest the difference?
Pure math: if your mortgage rate < expected investment return (and you're in a Roth or pre-tax bucket), invest. At a 6.5% mortgage and 7% S&P real return, it's nearly a wash. Below 5% mortgage, investing usually wins. Above 7%, prepayment is the safer bet because it's a guaranteed return.
What's the biweekly mortgage trick?
Pay HALF your mortgage every two weeks instead of the full amount monthly. 26 half-payments per year = 13 monthly equivalents (vs 12 with monthly billing). It's effectively one extra full payment per year, applied to principal — which trims about 5–7 years off a 30-year mortgage. Set this up directly with your servicer; never pay a third party for it.
Does an extra principal payment lower my monthly payment?
No. The monthly payment stays the same — extra payments just shorten the loan term by reducing the principal faster. To actually lower your payment, you'd need to refinance or recast (some lenders offer recasting after a lump-sum principal payment, which re-amortizes at the new lower balance).
Can I make extra payments on any mortgage?
Almost always yes — federal law prohibits prepayment penalties on most owner-occupied home loans (Dodd-Frank, 2010). Specify 'apply to principal' on every extra payment so the servicer doesn't credit it as next month's installment. Check your loan documents to confirm there's no penalty.
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