Auto Loan Calculator: Audit the Dealer Quote, Fees, APR & Total Cost
Enter your dealer's worksheet or build your own estimate from scratch. This deal auditor independently computes the amount financed, monthly payment, fees, negative equity, tax basis and total cost — then compares your dealer's figures against the math, shows preapproval savings and solves for a target payment.
Summary
Dealer quote reconciliation
Enter the dealer's quoted amount financed and monthly payment above to see the reconciliation.
Deal build-up (line items)
| Line item | Amount |
|---|---|
| Vehicle price | $40,000.00 |
| + Destination charge | $0.00 |
| + Dealer accessories | $0.00 |
| + Optional add-ons | $0.00 |
| Gross vehicle and products | $40,000.00 |
| + Sales tax (on $40,000.00 taxable) | $2,800.00 |
| + Title and registration | $400.00 |
| + Dealer fees | $300.00 |
| Total tax and fees | $3,500.00 |
| + Trade-in payoff rolled in | $0.00 |
| − Down payment | −$5,000.00 |
| − Trade-in credit | −$0.00 |
| − Cash rebate | −$0.00 |
| − Tax/fees paid upfront | −$0.00 |
| Amount financed | $38,500.00 |
Preapproval comparison
Enter a preapproval APR above to see the comparison.
Rebate vs promotional APR
- Amount financed
- $38,500.00
- Monthly payment
- $762.35
- Total of payments
- $45,740.77
- Total interest
- $7,240.77
- Amount financed
- $38,500.00
- Monthly payment
- $641.67
- Total of payments
- $38,500.00
- Total interest
- $0.00
Positive savings means the promo APR saves more total money than taking the rebate at the dealer rate. The break-even APR is the rate at which both options cost the same.
Loan-to-value (LTV) diagnostics
Enter an estimated vehicle value above to see LTV diagnostics.
Target payment solver
Enter a target monthly payment above to see the solver results.
Questions to ask your dealer
- Based on the figures entered, no major discrepancies were detected. Review each line item on the buyer order before signing.
This tool independently recalculates the figures entered. It does not determine whether a fee is lawful, mandatory or negotiable, and it does not replace the lender's contract or an official tax calculation.
Rebate vs promotional APR: how to decide
Manufacturers often require you to choose between a cash rebate and a promotional (sometimes 0%) APR. They look similar but work very differently. A rebate lowers the amount financed at the standard market rate. A promotional APR keeps the full purchase price but charges less interest over the term.
The break-even APR is the standard rate at which the rebate scenario and the promo scenario cost exactly the same total. If the dealer's rate is below that break-even APR, the promo wins; if it is above, the rebate wins. Enter both scenarios and decide on total of payments — not monthly payment.
Negative equity and the cost of rolling it forward
Negative equity (being upside down) means you owe more on the trade-in than it is worth. The shortfall is added to the new loan as if it were part of the vehicle price. You then pay interest on the new car and on the old balance simultaneously, which inflates both the monthly payment and the total cost.
This calculator isolates the negative equity amount and estimates the additional interest it costs over the loan term. If that figure is large, the better move may be to pay off the old balance separately before trading in, or to postpone the purchase until the equity gap closes.
LTV and lender risk tiers
Loan-to-value (LTV) compares the amount financed to the vehicle's market value. Lenders use LTV to set rate tiers: loans above 110% or 120% LTV often carry higher rates or require additional down payment. A new car can drop significantly in value immediately after purchase, so a loan with no down payment on a fully priced vehicle starts underwater.
Enter your estimated vehicle value (from Kelley Blue Book, NADA or your lender's guide) to see your starting LTV and how much extra cash at signing would bring it to 100%, 90% or 80%.
Evidence, sources and editorial review
Auto Loan Calculator: Audit the Dealer Quote, Fees, APR & Total Cost groups its evidence and methodology review here so sources, assumptions and responsibility can be checked together.
Methodology
The monthly payment uses the fixed-rate PMT formula on the amount financed, built from vehicle price, destination charge, dealer accessories, optional add-ons, sales tax (computed from a configurable taxable base — vehicle price, price minus trade-in, price minus rebate, price minus both, or a custom amount), title and registration fees, four dealer-fee categories, trade-in payoff (including negative equity rolled in), down payment, trade-in value and cash rebate. Taxes and fees paid upfront are excluded from the loan. The dealer quote reconciliation section compares the independently computed amount financed and theoretical payment against what the dealer quoted. The preapproval comparison recomputes at the lower rate and solves for the equivalent price cut. The promo APR vs cash-rebate comparison recomputes both scenarios and bisects for the break-even APR and break-even rebate. LTV diagnostics divide the amount financed by an estimated vehicle value. The target payment solver bisects for the required APR, extra down payment or vehicle price reduction. All figures are locked by golden tests that run on each build.
Reviewed according to the CalcDomain Editorial Policy & Calculator Methodology. We document formulas, edge cases, sources, update dates, and correction paths for calculator pages.
Updated
References & Authoritative Sources
- CFPB — Consumer Financial Protection Bureau — Auto loan guide and dealer financing · consulted June 27, 2026 · Federal consumer protection — auto loan APR, dealer markups, add-ons and total cost disclosure
- AAA — Your Driving Costs Annual Report — Total cost of vehicle ownership benchmark · consulted June 27, 2026 · Annual benchmark — full ownership cost beyond the loan payment (insurance, fuel, depreciation)
- Federal Reserve — Consumer Credit (G.19) — Auto loan interest rate statistics · consulted June 27, 2026 · Authoritative source — current US auto loan APR averages by lender type and maturity
Data Sources & Rate Benchmarks
The Federal Reserve G.19 rate shown below is the average for new-car 48-month loans from commercial banks — a reference benchmark only. Your actual rate depends on your credit, the lender and the loan term. Always get at least one bank or credit-union preapproval to compare against the dealer's offer.
Frequently Asked Questions
How does this calculator differ from a basic auto loan calculator?
A basic calculator takes an amount financed and outputs a payment. This deal auditor builds the amount financed from every line item on the dealer's worksheet — vehicle price, destination charge, accessories, add-ons, multiple fee categories, a configurable tax basis, trade-in equity or negative equity, and cash rebates. It then compares your computed figures against the dealer's quoted numbers, shows how a preapproval or promotional APR changes the cost, checks LTV, and solves for a target payment.
What is the amount financed, and why does it differ from the vehicle price?
The amount financed is what you actually borrow. It equals the gross vehicle and products total plus financed taxes and fees plus any trade-in payoff rolled in, minus your down payment, trade-in credit and cash rebate. Sales tax, dealer fees and negative equity can add thousands to the amount financed above the sticker price.
How does the tax basis mode affect the sales tax calculation?
States differ on what they tax. Some tax only the vehicle price; others subtract the trade-in or rebate before applying the rate; a few have their own custom rules. Choose the mode that matches your state. If you are unsure, mode 0 (vehicle price only) is a common default, but check with your state DMV or tax authority.
What is negative equity, and why does it matter?
Negative equity (or being underwater) means you owe more on the car you are trading in than it is worth. The shortfall is rolled into the new loan, raising both the amount financed and the interest you pay. This calculator shows the negative equity amount and the interest cost it adds over the loan term.
Should I take the cash rebate or the promotional APR?
Enter the rebate scenario (your APR, with the rebate) in the main form and set the promo APR field to the promotional rate. The promo comparison computes the full no-rebate scenario and bisects for the break-even APR and break-even rebate so you can see which option saves more total money. On short terms and smaller loans the rebate often wins; on long terms and large loans a deep APR cut can pull ahead.
What does the dealer quote reconciliation do?
If you enter the dealer's quoted amount financed and monthly payment, the calculator independently recomputes both figures from your entered line items and flags the delta. A large discrepancy in the amount financed often means undisclosed fees or add-ons are embedded in the dealer's figure. A payment discrepancy at the same amount financed can indicate a rate markup or calculation error.
How does the preapproval comparison work?
Enter your bank or credit union preapproval APR. The calculator recomputes the monthly payment and total of payments at that rate on the same amount financed and shows the monthly and total savings. It also bisects to find the equivalent vehicle price cut — the reduction you would need to negotiate to achieve the same savings at the dealer's APR.
What is LTV, and why does it affect my loan?
Loan-to-value (LTV) is the amount financed divided by the vehicle's market value, expressed as a percentage. Lenders often use LTV to set rate tiers or to decide whether to approve the loan. Enter an estimated market value (from Kelley Blue Book, NADA or your lender) to see your LTV and how much extra down payment would bring it to 100%, 90% or 80%.
How does the target payment solver work?
Enter a monthly payment goal. The solver bisects to find the APR that produces exactly that payment on the current amount financed, the extra down payment needed at the current APR, and the vehicle price reduction needed at the current APR. All three are shown so you can decide which lever to negotiate.
Are 72- or 84-month auto loans a good idea?
They lower the monthly payment but raise total interest and keep you underwater longer, because the car depreciates faster than the balance falls. A 60-month term is a sensible ceiling for a new car and 48 months for an older used one. If you need 72 or 84 months to afford the payment, that is usually a sign to look at a cheaper vehicle.
What dealer fees are included?
The calculator separates four fee categories: the dealer documentation (doc) fee, an electronic filing fee, a dealer prep fee and a catch-all other dealer fees field. Doc fees are sometimes negotiable and are capped by state law in some states. Prep fees and filing fees vary widely. Ask for an itemized breakdown of every fee on the buyer's order.
Does this replace my lender's contract or an official tax calculation?
No. This tool independently recalculates the figures you enter. It does not determine whether a fee is lawful, mandatory or negotiable, and it does not replace the lender's contract or an official tax calculation. Use it to understand the math and identify questions to ask before signing.
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What this deal auditor actually calculates
Most auto loan tools ask for a loan amount, rate and term. This calculator works the other way: you enter every line item on the dealer's worksheet and it builds the amount financed from scratch — vehicle price, destination charge, dealer accessories, optional add-ons, a state-specific taxable base, title and registration, four dealer-fee categories, trade-in equity or negative equity, cash rebates and the upfront vs financed split of taxes and fees.
That independently derived amount financed is then compared against the dealer's quoted figures. A discrepancy in the amount financed often means undisclosed add-ons or fees are embedded in the dealer's number. A discrepancy in the monthly payment at the same amount financed can indicate a rate markup. Seeing the math side by side gives you specific, numbered questions to bring back to the dealer.
Suggest an improvement
Found a calculation issue, outdated source, unclear assumption, or missing edge case? Send a short note so we can review it.
Update history
Last updated .
| Date | Version | Change |
|---|---|---|
| 2026-07-25 | 2.0 | Expanded from basic auto loan calculator to full dealer deal auditor with fee audit, preapproval comparison, rebate vs promo APR, LTV diagnostics and target payment solver |