*This includes your down payment and trade-in value, adjusted for sales tax.
How to Use the Car Loan Affordability Calculator
Buying a car is one of the most significant financial decisions you will make. Instead of walking into a dealership and asking "What is the monthly payment?", you should walk in knowing exactly what the total purchase price should be. Our Car Loan Affordability Calculator helps you reverse-engineer your budget to find a realistic vehicle price tag.
The 20/4/10 Rule of Car Buying
Financial experts often recommend the 20/4/10 rule to ensure your vehicle doesn't become a financial burden:
20% Down Payment: Aim to put at least 20% down to avoid "gap" issues where you owe more than the car is worth.
4-Year Term: Try to limit the loan term to 48 months (4 years) to minimize interest and match the car's depreciation.
10% of Income: Your total transportation costs (loan payment, insurance, gas, and maintenance) should not exceed 10% of your gross monthly income.
Understanding the Inputs
To get the most accurate results from this calculator, you need to understand how each variable impacts your buying power:
Desired Monthly Payment: This is the amount you are comfortable spending every month. Remember to leave room for insurance and fuel!
Interest Rate (APR): This is determined by your credit score. Excellent credit usually earns rates between 3-5%, while subprime credit can result in rates upwards of 15-20%.
Loan Term: While a 72 or 84-month loan makes the monthly payment lower, you will pay significantly more in interest over the life of the loan. A 60-month term is a standard middle ground.
Example Calculation
Let's say you can afford $500 per month. You have $5,000 in cash and a trade-in worth $2,000. If you qualify for a 6% interest rate over 60 months, and your local sales tax is 7%:
The loan you can afford is approximately $25,860.
Adding your $7,000 total down payment/trade-in gives you more room.
Adjusting for tax, you can shop for a car with a sticker price of roughly $30,700.
Tips for Lowering Your Car Costs
Improve Your Credit Score: Even a 1% drop in interest rates can save you thousands over 5 years.
Shop for Financing First: Get a pre-approval from a credit union or bank before visiting the dealership.
Factor in Hidden Costs: Don't forget registration fees, documentation fees, and the cost of ownership.
function calculateAffordability() {
var monthlyPayment = parseFloat(document.getElementById("monthlyPayment").value);
var downPayment = parseFloat(document.getElementById("downPayment").value) || 0;
var tradeIn = parseFloat(document.getElementById("tradeIn").value) || 0;
var annualRate = parseFloat(document.getElementById("interestRate").value);
var months = parseInt(document.getElementById("loanTerm").value);
var salesTax = parseFloat(document.getElementById("salesTax").value) || 0;
if (isNaN(monthlyPayment) || monthlyPayment <= 0 || isNaN(annualRate) || isNaN(months)) {
alert("Please enter valid numbers for payment, interest rate, and term.");
return;
}
// Monthly interest rate
var i = (annualRate / 100) / 12;
var loanAmount = 0;
if (i === 0) {
loanAmount = monthlyPayment * months;
} else {
// PV = Pmt * [(1 – (1 + i)^-n) / i]
loanAmount = monthlyPayment * ( (1 – Math.pow(1 + i, -months)) / i );
}
var totalDown = downPayment + tradeIn;
// Total vehicle price before tax calculation
// Price + (Price * Tax) = Loan + Down
// Price * (1 + Tax) = Loan + Down
// Price = (Loan + Down) / (1 + Tax)
var taxDecimal = salesTax / 100;
var totalVehiclePrice = (loanAmount + totalDown) / (1 + taxDecimal);
var totalInterest = (monthlyPayment * months) – loanAmount;
// Display results
document.getElementById("totalPrice").innerText = "$" + totalVehiclePrice.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("loanAmountResult").innerText = "$" + loanAmount.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("totalInterestResult").innerText = "$" + totalInterest.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("result-area").style.display = "block";
// Smooth scroll to result
document.getElementById("result-area").scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}