Auto Loan APR Calculator with Extra Payments
This calculator estimates scheduled payments, total interest, and the impact of extra payments on auto loans. Use it to compare a standard schedule to scenarios with one‑time or recurring extra contributions and to see approximate time and interest savings.
The tool supports monthly schedules and a dedicated bi‑weekly accelerated mode. Results are estimates for planning and do not replace lender payoff quotes; always verify final payoff amounts with your lender.
Compute scheduled periodic payment, total amount paid and total interest for a fixed-rate auto loan using the provided APR, term, and payment frequency.
Inputs
Results
Scheduled payment
$471.78
Number of payments
60
Total interest
$3,306.85
| Output | Value | Unit |
|---|---|---|
| Scheduled payment | $471.78 | USD |
| Number of payments | 60 | — |
| Total interest | $3,306.85 | USD |
Visualization
Methodology
Calculations use standard amortization formulas for fixed-rate installment loans. Periodic rate = APR / payments_per_year. Scheduled payment is the annuity payment that amortizes principal over the specified number of periods.
Recurring extras are converted to a per‑payment basis when the user provides a monthly extra and the payment frequency differs. One‑time extras are applied in the period specified by the UI (default: immediately). Payoff estimates with extras use the closed‑form inverse of the annuity formula to estimate the new number of periods; this is an analytical approximation that assumes extras are applied consistently each period.
For secure handling and engineering controls, implementation should follow NIST guidelines for secure development and IEEE best practices for numerical stability. Quality management and process controls should align with ISO 9001 principles; workplace safety for any staff involved follows OSHA guidance.
Further resources
External guidance
Expert Q&A
Does this calculator give an exact lender payoff?
No. This calculator provides estimates based on standard amortization math. Actual lender payoff amounts can include daily interest accrual methods, fees, rounding rules, or different compounding conventions. Always request a payoff statement from your lender for an exact figure.
Can I use monthly extras with bi‑weekly payments?
Yes. If you enter a monthly extra and choose a bi‑weekly schedule, the calculator converts the monthly amount into an equivalent per‑payment amount for the chosen payment frequency before estimating payoff effects.
Are the results compliant with any standards?
The numeric methods are standard financial formulas. For implementation and data handling we recommend following NIST guidance for secure software development, IEEE principles for numerical stability, ISO 9001 for quality management processes, and OSHA for workplace safety. This calculator is for planning and informational use and is not a regulated disclosure.
How accurate are the payoff and interest‑saved estimates?
Estimates are accurate for loans using consistent periodic interest accrual and fixed payments. Differences may arise from daily interest accrual, lender rounding, applied fees, payment timing, or if the lender applies extras differently. Expect small variances; treat results as a planning guide.
Sources & citations
- NIST Cybersecurity Framework & Secure Dev Guidance — https://www.nist.gov/cyberframework
- ISO — Quality management (ISO 9001) — https://www.iso.org/iso-9001-quality-management.html
- IEEE — Standards and resources — https://www.ieee.org
- OSHA — Occupational Safety and Health Administration — https://www.osha.gov