function calculateCarLoan() {
// Get input values
var vehiclePrice = parseFloat(document.getElementById('vehiclePrice').value) || 0;
var downPayment = parseFloat(document.getElementById('downPayment').value) || 0;
var tradeInValue = parseFloat(document.getElementById('tradeInValue').value) || 0;
var salesTaxRate = parseFloat(document.getElementById('salesTax').value) || 0;
var interestRate = parseFloat(document.getElementById('interestRate').value) || 0;
var loanTerm = parseInt(document.getElementById('loanTerm').value) || 60;
// Validation
if (vehiclePrice <= 0) {
alert("Please enter a valid vehicle price.");
return;
}
// Logic for Sales Tax Calculation
// Generally, sales tax is applied to the price minus trade-in in many states,
// but sometimes full price. We will assume (Price – TradeIn) * Tax for this standard model.
var taxableAmount = Math.max(0, vehiclePrice – tradeInValue);
var salesTaxAmount = taxableAmount * (salesTaxRate / 100);
// Calculate Total Price (Vehicle + Tax)
// Note: Down payment reduces the amount to be financed, not the tax basis usually.
var totalPrice = vehiclePrice + salesTaxAmount;
// Calculate Amount Financed
var amountFinanced = totalPrice – downPayment – tradeInValue;
if (amountFinanced <= 0) {
document.getElementById('results').style.display = 'block';
document.getElementById('monthlyPaymentDisplay').innerText = "$0.00";
document.getElementById('loanAmountDisplay').innerText = "$0.00";
document.getElementById('salesTaxDisplay').innerText = "$" + salesTaxAmount.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('totalInterestDisplay').innerText = "$0.00";
document.getElementById('totalCostDisplay').innerText = "$" + totalPrice.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
return;
}
// Amortization Calculation
var monthlyRate = (interestRate / 100) / 12;
var monthlyPayment = 0;
var totalInterest = 0;
if (interestRate === 0) {
monthlyPayment = amountFinanced / loanTerm;
} else {
monthlyPayment = amountFinanced * (monthlyRate * Math.pow(1 + monthlyRate, loanTerm)) / (Math.pow(1 + monthlyRate, loanTerm) – 1);
}
var totalPaid = monthlyPayment * loanTerm;
totalInterest = totalPaid – amountFinanced;
var totalCost = totalPrice + totalInterest;
// Update DOM
document.getElementById('results').style.display = 'block';
document.getElementById('monthlyPaymentDisplay').innerText = "$" + monthlyPayment.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('loanAmountDisplay').innerText = "$" + amountFinanced.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('salesTaxDisplay').innerText = "$" + salesTaxAmount.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('totalInterestDisplay').innerText = "$" + totalInterest.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('totalCostDisplay').innerText = "$" + totalCost.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
}
Understanding Your Car Loan Options
Financing a vehicle is one of the most significant financial decisions many households make. This Car Loan Payment Calculator is designed to help you estimate your monthly auto loan payments accurately before you step foot in a dealership. By inputting factors like the vehicle price, your trade-in value, and the expected interest rate (APR), you can see a clear breakdown of your financial commitment.
Key Factors Affecting Your Monthly Car Payment
When calculating your auto loan, several variables directly impact how much you pay each month:
Vehicle Price: The negotiated purchase price of the car. Remember to negotiate the "out-the-door" price rather than just the monthly payment.
Down Payment & Trade-In: Putting more money down or trading in an old vehicle reduces the principal loan amount (the amount financed). This lowers both your monthly payment and the total interest paid over the life of the loan.
Interest Rate (APR): Your credit score significantly influences your APR. A lower rate can save you thousands of dollars. For example, on a $30,000 loan, the difference between 4% and 9% interest is substantial.
Loan Term: While a longer term (e.g., 72 or 84 months) lowers your monthly bill, it often increases the total cost of the car due to accumulating interest. Experts generally recommend keeping auto loans to 60 months or fewer if possible.
How Sales Tax Impacts Your Loan
Many buyers forget to factor in sales tax, which can add significant cost to the vehicle. In many jurisdictions, the sales tax is calculated based on the difference between the new car's price and your trade-in value. Our calculator estimates this tax to give you a more realistic "Amount Financed" figure, ensuring you aren't surprised by higher payments.
Tips for Lowering Your Auto Loan Costs
To get the best deal, secure financing pre-approval from a bank or credit union before visiting the dealership. This gives you leverage to negotiate the interest rate. Additionally, aim for a down payment of at least 20% to avoid "being upside down" on your loan (owing more than the car is worth) as soon as you drive off the lot.