Finance category
Mortgage, loan, investing, tax, and money calculators.
Mortgage Principal Prepayment Calculator
Even modest extra principal payments compound into large interest savings over a 30-year mortgage. This calculator shows interest saved and months cut from your payoff date by adding extra to each payment or making annual lump sums.
Total interest saved
$187,332
Months saved
11 yr
New payoff timing
15 yr 10 mo
Enhanced monthly payment
$2,667
How the math works
Adding principal to each payment shortens the amortization and saves interest — often dramatically on long-tail mortgages in early years. A modest $400/month extra on a 30-year mortgage typically cuts 5-7 years off the term.
Biweekly payment programs are functionally equivalent to one extra monthly payment per year. Annual lump sums (tax refund, bonus) accelerate payoff meaningfully without affecting monthly budget. Always confirm your servicer applies extras to principal, not future interest.
How to Use
- Enter current mortgage balance, rate, and months remaining.
- Enter extra principal per month — even $100 compounds meaningfully.
- Enter annual lump sum if you plan to send tax refunds or bonuses to principal.
- Read interest savings and months saved from your payoff date.
Frequently Asked Questions
Does biweekly payment work?
Yes, functionally — paying half your monthly payment every 2 weeks results in 26 half-payments (= 13 monthly payments) per year vs 12 monthly. Equivalent to 1 extra monthly payment per year spread evenly.
Will my servicer apply extras correctly?
Usually yes — write 'Apply to principal' on the payment and keep records. Most online servicers have a 'principal curtailment' option separate from regular payment. Review statements to confirm extras reduce principal, not pre-pay future interest.
Is prepaying better than investing?
Depends on your after-tax mortgage rate vs expected investment return. Use our Payoff vs Invest Calculator. Mathematically, investing wins at typical spreads — but prepayment provides guaranteed return and behavioral benefits.
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