Amortization & payoff modeling. Your loan figures are computed in your browser and never leave your device — nothing is uploaded, nothing is stored.
Loan
Most US issuers charge that month's interest plus 1–2% of the balance, with a $25–$35 floor. The payment shrinks as the balance falls, which is why minimums take so long.
Adds to the starting balance before interest accrues.
Prepayments
Applied 100% to principal on that payment number, after that month's interest.
On = extra money shortens the loan. Off = payment is recalculated over the remaining original term, lowering your payment instead.
Interest is computed on the balance at each period using APR ÷ 12. Real lenders may use daily accrual, so results can differ by a few dollars.