Loan Cost & Payoff Calculator
Calculate how much interest your loan costs, how long repayment will take, and how extra monthly payments can reduce your interest and payoff time.
Preparing your calculator…
MansionMath provides estimates for educational purposes. Actual loan terms, taxes, insurance, fees, investment returns, and eligibility may vary.
How this calculator works
How loan interest works: each month accrues interest on the opening balance. APR versus APY: nominal APR ÷ 1,200 gives the monthly decimal rate; APY uses (1 + APY ÷ 100)^(1/12) − 1. Minimum payments pay accrued interest first; the remainder reduces principal. Extra payments reduce future interest by lowering the balance, assuming penalty-free principal prepayments. Total loan cost is interest plus any contract fees (fees are excluded here); cash paid includes principal and must not be confused with interest expense. When payments do not cover interest, this model capitalizes unpaid interest and does not invent a payoff date. Later payments clear current and previously capitalized interest before original principal; contracts may use different allocation rules. This estimates historical costs from the supplied starting balance, not reconstructed bank records. It models monthly payments at period end, not daily simple-interest, variable-rate, deferred/student-loan subsidy, fee, or delinquency rules. Precision is retained internally; displayed currency is rounded. Loan years group consecutive blocks of 12 payments, not calendar years.
Use current quotes, local rates, and measured dimensions to make this estimate useful for your situation.
Frequently asked questions
Can I use this for personal, auto, or student loans?+
Yes when a fixed-rate monthly-amortization model matches your contract. Daily simple interest, payment-date variation, fees, subsidies, variable rates, and deferment can materially change actual costs.
What is the difference between APR and APY here?+
APR is modeled as a nominal annual rate divided into 12 monthly periods. APY is an effective annual rate converted to monthly growth. A legally disclosed loan APR may incorporate fees; this tool does not derive the contractual interest rate from a fee-inclusive APR.
What happens if payments do not cover interest?+
The balance may stay unchanged or grow because unpaid interest is capitalized here. No payoff date is shown unless the simulated payments actually clear the loan. A later one-time payment can change that outcome.
Is this exact historical interest paid?+
No. It is an estimate from a supplied starting balance, payment, and constant rate. It does not infer earlier history from only a current balance.
How are one-time payments and analysis dates handled?+
The extra applies with the chosen payment number, after accrued interest. A custom analysis month includes that month’s payment. Otherwise the selected number of months or years defines the period. Payments stop at payoff.