Please check your inputs. Ensure positive numbers are entered.
Estimated Monthly Payment:–
Total Loan Amount:–
Total Interest Paid:–
Total Cost (Loan + Interest):–
Payoff Date:–
Understanding Your Auto Loan Calculation
Purchasing a vehicle is one of the most significant financial decisions you will make. This Car Loan Amortization Calculator helps you estimate your monthly payments and understand the long-term cost of your loan. By inputting factors such as vehicle price, down payment, trade-in value, and interest rate (APR), you can determine exactly how much car you can afford.
Key Factors Affecting Your Monthly Payment
Vehicle Price & Sales Tax: The sticker price is just the beginning. Sales tax, which varies by state, is calculated on the vehicle price (often before trade-ins) and significantly increases the total loan amount.
Down Payment & Trade-In: These reduce the principal amount you need to borrow. A larger down payment reduces risk for the lender, which can sometimes help you secure a lower interest rate.
Interest Rate (APR): Your credit score largely determines your APR. Even a 1% difference in interest can save—or cost—you hundreds or thousands of dollars over the life of the loan.
Loan Term: Longer terms (e.g., 72 or 84 months) lower your monthly payment but drastically increase the total interest paid. Shorter terms (e.g., 36 or 48 months) have higher monthly costs but save money in the long run.
What is Loan Amortization?
Amortization refers to the process of paying off debt with a fixed repayment schedule in regular installments over a period of time. In the early stages of a car loan, a higher percentage of your payment goes toward interest. As the loan matures, more of your payment is applied to the principal balance, accelerating equity building in your vehicle.
How to Use This Calculator
Enter the negotiated price of the car in the "Vehicle Price" field. Subtract any cash down payment and the value of your old car in the "Trade-in Value" field. Don't forget to include the estimated sales tax rate for your area to get a realistic total. Adjust the "Loan Term" to see how extending or shortening the loan affects your monthly budget.
function calculateCarLoan() {
// Clear previous errors
document.getElementById('errorMsg').style.display = 'none';
document.getElementById('resultsArea').style.display = 'none';
// Get Input Values
var price = parseFloat(document.getElementById('vehiclePrice').value);
var down = parseFloat(document.getElementById('downPayment').value);
var trade = parseFloat(document.getElementById('tradeInValue').value);
var taxRate = parseFloat(document.getElementById('salesTax').value);
var interestRate = parseFloat(document.getElementById('interestRate').value);
var months = parseInt(document.getElementById('loanTerm').value);
// Validation – Check for NaN
if (isNaN(price)) price = 0;
if (isNaN(down)) down = 0;
if (isNaN(trade)) trade = 0;
if (isNaN(taxRate)) taxRate = 0;
if (isNaN(interestRate)) interestRate = 0;
// Basic validation logic
if (price <= 0 && down <= 0) {
document.getElementById('errorMsg').style.display = 'block';
document.getElementById('errorMsg').innerText = "Please enter a valid Vehicle Price.";
return;
}
// Calculation Logic
// 1. Calculate Tax Amount (Usually Tax is on the Vehicle Price, sometimes price minus trade-in depending on state.
// We will assume Tax is on (Price – TradeIn) for a generic "Tax Credit" state scenario, or just Price if no trade.
// Let's go with Tax on Price for a conservative estimate (higher cost).
var taxAmount = price * (taxRate / 100);
// 2. Calculate Total Loan Amount (Principal)
// Principal = (Price + Tax) – Down Payment – Trade In
var principal = (price + taxAmount) – down – trade;
if (principal <= 0) {
document.getElementById('errorMsg').style.display = 'block';
document.getElementById('errorMsg').innerText = "Your Down Payment and Trade-in cover the cost of the car!";
return;
}
// 3. Monthly Payment Formula: M = P * [ r(1+r)^n ] / [ (1+r)^n – 1 ]
// r = monthly interest rate (annual / 12)
// n = number of months
var monthlyPayment = 0;
var totalInterest = 0;
var totalCost = 0;
if (interestRate === 0) {
// Simple division for 0% financing
monthlyPayment = principal / months;
totalInterest = 0;
totalCost = principal;
} else {
var monthlyRate = (interestRate / 100) / 12;
var mathPower = Math.pow(1 + monthlyRate, months);
monthlyPayment = principal * ((monthlyRate * mathPower) / (mathPower – 1));
totalCost = monthlyPayment * months;
totalInterest = totalCost – principal;
}
// Calculate Payoff Date
var today = new Date();
today.setMonth(today.getMonth() + months);
var options = { year: 'numeric', month: 'long' };
var payoffDateStr = today.toLocaleDateString("en-US", options);
// Display Results
// Format numbers to currency
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2
});
document.getElementById('monthlyPaymentResult').innerText = formatter.format(monthlyPayment);
document.getElementById('totalLoanAmount').innerText = formatter.format(principal);
document.getElementById('totalInterestResult').innerText = formatter.format(totalInterest);
document.getElementById('totalCostResult').innerText = formatter.format(totalCost);
document.getElementById('payoffDate').innerText = payoffDateStr;
document.getElementById('resultsArea').style.display = 'block';
}