US Finance Tool
Auto Loan Calculator — the whole deal, not just the payment
A car payment is decided long before the APR. It is decided by the trade-in tax credit your state does or does not give you, by whether you still owe money on the car you are trading, and by a term that makes the monthly figure look reasonable while quietly adding thousands in interest. This calculator works the deal from sticker price to signed contract and shows each of those separately.
- 🔁 Trade-in tax credit
- ⚠️ Negative equity roll-in
- 📊 36–84 month comparison
- 🔒 Nothing leaves your browser
The deal
Everything updates as you type.
Start from a common case
Depreciation assumptions
Used only for the underwater estimate. Change them to match your own car — a truck and a luxury sedan do not lose value at the same rate.
Your payment
—
| Vehicle price | — |
| Sales tax | — |
| Dealer & state fees | — |
| Cash down | — |
| Trade-in equity | — |
| Amount financed | — |
Over the life of the loan
- Total interest
- —
- Total repaid
- —
- Paid off in
- —
- Total out of pocket
- —including cash down
Every term compared
Same amount financed, same APR — only the term changes.
| Term | Payment | Total interest | Total paid |
|---|
When do you stop owing more than it is worth?
Loan balance against the car's value
Where the balance line sits above the value line, you are underwater. Depreciation is an estimate from the rates you set.
Not financial advice. This calculator produces estimates for planning from the figures you enter. It is not a loan offer, a rate quote or financial, tax or legal advice. Sales tax rules, trade-in credits, fee caps and titling costs vary by state and change; confirm your own state's treatment before relying on the tax line. Your lender's contract and the dealer's buyer's order are the authoritative documents.
The trade-in tax credit is worth real money
This is the single most misunderstood line in a US car deal. In most states, sales tax is charged on the purchase price minus your trade-in allowance. Trade a car worth $10,000 against a $30,000 purchase in a 7% state and you are taxed on $20,000, not $30,000 — the trade-in has just saved you $700 on top of its own value.
A minority of states do not do this and tax the full price regardless. California, Virginia, Maryland and Hawaii are the commonly cited examples, and Michigan caps the credit rather than granting it in full. The tick box above switches between the two treatments.
It matters because it changes a real decision. Selling privately usually gets you more than the dealer will allow — but in a credit state the dealer's offer comes with a tax saving attached, and a private sale does not. The private buyer has to beat the trade-in allowance plus the tax credit before it is worth the hassle. In a full-price state that calculation disappears entirely and selling privately is far more often the better deal.
Rolling negative equity forward
If you owe $12,000 on a car the dealer will allow $9,000 for, you are $3,000 underwater. That $3,000 does not go away when you sign. The dealer settles your old loan and adds the shortfall to the new one, so you finance $3,000 more than the new car costs.
The consequence compounds. You now begin the new loan already owing more than the car is worth, before it has left the lot or depreciated a mile. If you trade again in three years, the gap is likely to be larger still, and it rolls forward again. This is the mechanism by which people end up carrying debt from two or three cars ago on a vehicle they are still driving.
The calculator flags this explicitly whenever the amount financed exceeds the vehicle price. The way out is not a longer term — that makes it worse — but a larger down payment, a cheaper car, or keeping the current car until the balance falls below its value.
Why a longer term is not a cheaper car
Dealers negotiate in monthly payments because a monthly payment can be made to look like almost anything given enough months. Stretching a loan from 60 to 84 months genuinely does lower the payment — and genuinely does raise what the car costs you, every single time.
The term table above shows both columns together for exactly this reason. There is no term at which the payment falls and the total falls; that trade is fixed by the arithmetic. What you are deciding is how much extra you are willing to pay for a smaller monthly commitment.
The second cost is less visible. A car depreciates fastest early and a long loan retires principal slowest early, so the two curves diverge. On an 84-month loan with little down, you can spend most of the loan owing more than the car is worth — which means you cannot sell it without writing a cheque, and an insurance write-off leaves you paying for a car you no longer have.
A reasonable rule, if you want one: if you cannot afford the car on a 60-month term, the honest conclusion is usually that you cannot afford that car rather than that you need more months.
Frequently asked questions
What is the trade-in sales tax credit?
In most US states, sales tax is charged on the price minus your trade-in allowance rather than the full price. On a $30,000 car with a $10,000 trade-in at 7%, that is $1,400 of tax instead of $2,100 — the trade-in is worth $700 more than its sticker value. A minority of states, including California, Virginia and Maryland, tax the full price regardless. The tick box switches between the two.
What happens if I owe more on my trade-in than it is worth?
The shortfall does not disappear. The dealer pays off your old loan and adds the difference to the new one, so you finance more than the new car costs. The calculator shows this explicitly: the amount financed rises above the vehicle price and you start the loan already underwater.
Is a 72 or 84 month car loan a bad idea?
Not automatically, but it is always more expensive, and an affordable payment is not the same as a sensible loan. A longer term lowers the monthly figure and raises the total interest, and because the car depreciates faster than the loan amortizes, it keeps you underwater far longer. The term table shows both columns so the cost of the smaller payment is visible.
What does being underwater or upside down mean?
The loan balance is larger than the car is worth. If the car were written off, your insurer pays market value and you would still owe the difference. Almost every car loan starts underwater because a new car loses value fastest in year one. What matters is how long the gap lasts, and whether gap insurance is worth buying to cover it.
Are dealer fees negotiable?
Title, registration and licence fees go to the state and are fixed. The documentation fee goes to the dealer, is capped by law in some states and uncapped in others, and is often negotiable in practice — if not on the fee then on the price, which amounts to the same thing. They are entered separately because doc fees generally enter the taxable base and state fees do not.
Should I take the low APR or the cash rebate?
Run it both ways here. Enter the full price with the promotional APR, then the price minus the rebate with the rate your own bank or credit union would give, and compare total paid. Which wins depends on the rebate size, the rate gap and the term — there is no rule of thumb that holds, which is why it is worth calculating.
How accurate is the depreciation estimate?
It is an illustration, not a valuation. The model applies a larger first-year drop then a flat annual rate, and both are inputs you can change. Real depreciation varies enormously by make, model, mileage and market. Use it to understand the shape of the problem — the gap opens early and closes slowly — not as a forecast for your specific car.
Is my information sent anywhere?
No. Every calculation runs in your browser. The figures you type are saved only in your own browser's local storage so the page remembers them next visit, and clearing your site data removes them. Nothing about your finances is transmitted to ToolAdda.