Loan Extra-Payment Calculator
Find out what an extra payment does to any amortizing loan: car, personal, student, RV, boat. Exact month-by-month amortization, no approximations.
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Biweekly mode simulates 26 half-payments per year on the same APR, which is the schedule lenders actually run (24 monthly payments + 2 half-payments of extra cash flow a year).
How the math works
Required payment = P × r(1+r)ⁿ ÷ ((1+r)ⁿ−1), where r = APR/12 and n = remaining months. Standard annuity amortization.
Simulation: each month interest = balance × r, principal = payment + extra − interest. The loan ends when balance hits zero. Extra payments change nothing about the interest formula, they just shrink the balance faster, so interest stops accruing on money you already paid.
Biweekly: payment/2 every two weeks, interest = balance × APR/26. Same math, 26 periods a year. The payoff date assumes payments start now (dates are from today).
Precomputed payment + extra vs true biweekly are modeled separately; both are exact under the stated schedule.
Frequently asked questions
Does paying extra each month actually save interest?
Yes. Every extra dollar goes straight to principal, and principal is what interest is computed on. On a $20,000 car loan at 7% over 6 years, an extra $100 a month saves about $1,900 in interest and ends the loan roughly 22 months early.
Is biweekly payment better than monthly?
Biweekly payments of half your monthly payment make 26 half-payments a year, which is 13 full monthly payments instead of 12. That extra payment each year shortens the loan and saves interest, the same effect as adding one-twelfth of your payment each month.
Should I pay extra on a loan or invest?
Compare rates. Extra payments on a 7% loan give you a guaranteed 7% return, tax-free. Investing has to clear 7% after tax to beat it, so most people should clear high-rate debt first, then invest the difference.