Auto Loan Calculator

How to estimate an auto loan

Enter the vehicle price, annual rate used for this estimate, and a whole-month term. Expand Trade, tax, fees, and cash down to model the purchase in more detail. Choose Calculate auto loan only after the values and the two explicit treatment choices match the quote you want to compare.

The amount before tax and entered fees is vehicle price minus cash down and trade allowance, plus the amount still owed on the trade. This makes trade equity auditable: a $10,000 allowance with a $12,000 payoff is −$2,000 negative equity and increases the base amount financed by $2,000.

Choose the taxable basis instead of assuming a state rule

Vehicle sales-tax treatment is not uniform. California publishes an example where a trade allowance does not reduce the taxable selling price, while New York describes circumstances in which a qualifying trade-in allowance reduces the taxable receipt. This calculator therefore offers two assumptions: tax the full entered price, or subtract an eligible trade allowance and floor the basis at $0. It never infers a state, county, eligibility rule, or tax rate.

Estimated tax is calculated from the chosen basis and the rate you enter, then rounded once to the nearest cent using half-away-from-zero integer arithmetic. Your written purchase document controls; a dealer or tax authority can use different inclusions or rounding.

Financed versus upfront tax and fees

If tax and entered fees are financed, they are added once to principal and earn interest. If they are paid upfront, they are added once to the model's cash due and stay out of principal. The receipt repeats the choice, taxable basis, tax, fees, cash due, and amount financed so you can trace the result.

Payment formula and 0% handling

For a positive annual rate, the regular payment is L × r ÷ (1 − (1 + r)−n), where L is amount financed, r is the monthly rate, and n is the number of months. The implementation uses log1p and expm1 for a stable denominator. At exactly 0%, it uses L ÷ n directly and never divides by the positive-rate denominator.

Monthly and annual tables come from the same unrounded schedule. Each display value is rounded to cents; totals are sums of unrounded rows rounded once, rather than sums of already rounded cells. The final row pays the remaining unrounded balance plus that month's interest and forces the ending balance to exactly zero.

Limits and professional boundary

This browser-only V1 accepts plain nonnegative dollar decimals, tax from 0%–25%, an annual rate from 0%–100%, 1–120 whole months, and at most $20,000,000 financed. It estimates a fixed-rate, fully amortizing purchase loan with end-of-month payments.

It is an educational estimate, not a lender quote, contractual APR calculation, credit decision, affordability recommendation, tax determination, or financial or legal advice. It does not provide live rates, lender matching, automatic tax tables, leases, refinancing, balloon or biweekly plans, early payoff, rebates, insurance, maintenance, depreciation, or ownership-cost advice. Compare the full written out-the-door price, disclosures, and payment schedule with the dealer, lender, and relevant tax authority.

Browser-only privacy

The engine is bundled with this static page. Calculation, table expansion, reset, and receipt preparation do not fetch a rate or send application data. The calculator does not put entered or derived amounts in query parameters, URL fragments, local storage, session storage, IndexedDB, cookies, structured data, or analytics. Measurement is limited to fixed actions and fixed validation error codes with the canonical page address.