About this Auto Loan Calculator
Financing a car involves more than just the sticker price. Taxes, trade-ins, and interest rates all play a huge role in your final monthly payment. This tool helps you negotiate better by showing you the real monthly cost before you step onto the lot.
Who this calculator is for
- Car buyers comparing dealership offers before they sign paperwork.
- Borrowers who need to understand the effect of trade-ins, tax, and term length on payment.
- Anyone trying to avoid an oversized payment or negative equity situation.
When to use it
- Use this calculator when you have a negotiated price and want to estimate the full financed amount.
- Compare 60-month and 72-month loans to see how much lower payments really cost in flexibility and risk.
- Review the payment with your DTI if you are also planning a mortgage or other major loan.
How to use this calculator
- Enter the Vehicle Price (the negotiated price, not necessarily MSRP).
- Enter any Trade-in Value for your old car.
- Add your cash Down Payment.
- Adjust the Interest Rate and Sales Tax to match your state and credit profile.
Key assumptions
- Sales tax is estimated from the vehicle price less trade-in value, which matches many but not all state rules.
- The loan uses fixed monthly payments and does not model dealer fees, registration, or optional add-ons.
- Trade-in and down payment are applied immediately to reduce the financed amount.
Accuracy and testing
Review formula sources, default test cases, assumptions, unit handling, rounding rules, and changelog for this calculator.
How this calculator works
Inputs explained
Vehicle Price
The price you agree to pay for the car. Negotiate this first before discussing monthly payments.
Trade-in Value
The amount the dealer gives you for your old car. In many states, this amount reduces the taxable price of the new car.
Sales Tax
The percentage tax charged by your state/county. Auto sales tax can be significant (e.g., 7% on a $30k car is $2,100).
Term (Months)
Common terms are 36, 48, 60, 72, or 84 months. Longer terms lower payments but drastically increase total interest.
Understanding your results
Example scenarios
Standard Purchase
A $35,000 car with a $5,000 trade-in and $2,000 cash down leaves $28,000 taxable. With 6% tax ($1,680) added, the loan is ~$29,680. At 6% interest for 60 months, the payment is ~$574.
Zero Down Risk
Buying the same car with $0 down and 0 trade-in means financing the full price + tax (~$37,100). The payment jumps to ~$717, and you immediately owe more than the car is worth.
Key Features
- Trade-in logic included
- Sales tax calculation
- Negative equity warnings
Things to Keep in Mind
This calculator provides an estimate. Actual dealership offers may vary based on credit score tiers, documentation fees ($85-$500 depending on state), and title/registration costs which are not included here.
Tips & Best Practices
- The '20/4/10' rule suggests putting 20% down, financing for no more than 4 years, and keeping payments under 10% of your gross income.
- Avoid 72 or 84-month loans if possible. You will likely owe more than the car is worth for several years (negative equity).
- Get pre-approved by a credit union before visiting the dealership to lock in a better interest rate.
Glossary of Terms
- Upside Down
- Owing more on your car loan than the vehicle is currently worth.
- APR
- Annual Percentage Rate. The yearly rate of interest charged to borrowers.
- Depreciation
- The decline in a car's value over time. New cars lose ~20% of their value in the first year.