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Car Price Budget from Payment, Trade-In & Tax

Estimate a car purchase price from a monthly loan budget, cash down, net trade-in equity and tax on the full price.

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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Use the result with context

Results are estimates for planning and education. Confirm rates, taxes, fees, and legal requirements with the relevant institution or a qualified professional before making a financial decision.

Formula and method

At zero interest, twelve payments of 1,000 support a 12,000 loan. Add 2,000 cash and 8,000 net trade-in equity; with 10 percent tax on the full price, the car budget is 20,000.

Car price = (supported loan + cash + net trade-in equity)/(1 + sales tax rate)

Worked example

Enter these known values and leave the other values blank.

Monthly loan-payment budget
1000 USD
Cash available toward purchase
2000 USD
Net trade-in equity after payoff
8000 USD
Annual nominal interest rate
0 %
Modeled loan term
1:0 yrs / mos
Tax rate on the full car price
10 %
Supported car price before tax
20000 USD
Supported financed principal
12000 USD
Estimated total loan interest
0 USD
Estimated sales tax
2000 USD

Assumptions and limitations

  • The model uses a fixed nonnegative nominal rate, equal end-of-period payments and no extra payments, balloon balance, fees or missed payments.
  • At zero interest, principal equals payment times the number of periods. A positive financed balance needs a payment above periodic interest to amortize in finite time.
  • Whole payment counts describe an equal-payment schedule. Fractional terms are continuous mathematical estimates, not exact calendar payoff dates or final partial bills.
  • The calculator retains internal precision. Contractual rounding, daily accrual and irregular dates can change an actual repayment schedule.
  • The annual rate is divided by twelve. Cash and net trade-in equity are nonnegative. Subtract any outstanding trade-in loan before entering equity; negative equity is outside this model.
  • Sales tax is applied to the full car price. Local trade-in tax credits, rebates, fees, registration and insurance are not included.
  • This is budget arithmetic, not a lender approval or a recommendation to spend the maximum.

Common questions

Should I enter the whole trade-in offer?

Only if no loan remains on the trade-in. Otherwise enter the offer minus its payoff balance, provided that equity is nonnegative.

Does this apply a trade-in sales-tax credit?

No. It taxes the full modeled car price. Jurisdictions with a credit need a different tax calculation.

References

Bookify handles zero interest in the financed-principal equation and payment inverse. Bookify accepts no cash down, requires nonnegative trade-in equity and tax, and validates a positive amortizing loan.

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