Auto Loan Extra Payments Calculator with Bi-Weekly Payments

We compute a periodic interest rate by dividing the annual nominal APR by the number of payment periods per year (26 for bi‑weekly, 12 for monthly). The scheduled payment solves the annuity formula for the periodic payment.

When extra per‑payment amounts are added, we treat the combined amount as the effective payment in the amortization equations and use a closed‑form logarithmic solution to estimate remaining number of payments.

For a lump sum applied at a specific month on a monthly schedule, we compute the outstanding balance immediately before the lump sum using the standard balance formula, subtract the lump sum from principal, and then compute the remaining payments from that reduced balance.

Use bi‑weekly per‑payment extra calculations to see how regular extra contributions change payoff time and interest cost.

Use the lump‑sum tool for one‑time principal reductions and to compare impact versus steady extra payments.

Treat outputs as a mathematical model. Confirm lender posting rules, fees, and prepayment policies before making decisions.

Example 1: $20,000 loan, 5% APR, 5 years. Adding $50 to each bi‑weekly payment reduces the payoff time and can save several hundred dollars in interest versus making no extras.

Example 2: $15,000 loan, 4.5% APR, 4 years. Applying a $2,000 lump sum at month 12 lowers the remaining balance and shortens the subsequent payment stream; the tool shows new years to payoff and interest saved.