function calculateCarLoan() {
var vPriceStr = document.getElementById("vehiclePrice").value;
var dPaymentStr = document.getElementById("downPayment").value;
var tInValueStr = document.getElementById("tradeInValue").value;
var iRateStr = document.getElementById("interestRate").value;
var termStr = document.getElementById("loanTermMonths").value;
var vPrice = parseFloat(vPriceStr);
var dPayment = parseFloat(dPaymentStr) || 0;
var tInValue = parseFloat(tInValueStr) || 0;
var iRate = parseFloat(iRateStr);
var termMonths = parseInt(termStr);
if (isNaN(vPrice) || vPrice <= 0 || isNaN(iRate) || iRate < 0) {
alert("Please enter valid positive numbers for Vehicle Price and Interest Rate.");
return;
}
// Calculate Loan Principal
var principal = vPrice – dPayment – tInValue;
if (principal <= 0) {
document.getElementById("calcResult").style.display = "block";
document.getElementById("monthlyPaymentOut").innerText = "$0.00";
document.getElementById("totalPrincipalOut").innerText = "$0.00";
document.getElementById("totalInterestOut").innerText = "$0.00";
document.getElementById("totalCostOut").innerText = "$" + (dPayment + tInValue).toFixed(2);
return;
}
var monthlyRate = (iRate / 100) / 12;
var monthlyPayment = 0;
var totalInterest = 0;
if (monthlyRate === 0) {
monthlyPayment = principal / termMonths;
} else {
// Amortization Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
var x = Math.pow(1 + monthlyRate, termMonths);
monthlyPayment = (principal * monthlyRate * x) / (x – 1);
}
var totalPaidOverTerm = monthlyPayment * termMonths;
totalInterest = totalPaidOverTerm – principal;
var totalCostOfCar = vPrice + totalInterest;
document.getElementById("monthlyPaymentOut").innerText = "$" + monthlyPayment.toFixed(2);
document.getElementById("totalPrincipalOut").innerText = "$" + principal.toFixed(2);
document.getElementById("totalInterestOut").innerText = "$" + totalInterest.toFixed(2);
document.getElementById("totalCostOut").innerText = "$" + totalCostOfCar.toFixed(2);
document.getElementById("calcResult").style.display = "block";
}
Understanding Your Car Loan Options
Financing a new or used vehicle is a significant financial commitment. Our Car Loan Calculator helps you understand the monthly impact of purchasing a vehicle by factoring in essential elements beyond just the sticker price. By inputting your potential down payment, trade-in value, and secured interest rate, you can determine a realistic budget before stepping onto the dealership lot.
Key Factors affecting Auto Loans
Vehicle Price: The negotiated purchase price of the car, truck, or SUV, including any dealer fees or add-ons, before tax.
Down Payment & Trade-in: Money paid upfront or equity from your previous vehicle reduces the total amount you need to borrow. A larger down payment significantly lowers both your monthly payment and total interest paid.
Interest Rate (APR): The annual percentage rate charged by the lender. Rates depend on your credit score, the type of vehicle (new vs. used), and current market conditions. Even a 1% difference can save hundreds of dollars over the life of the loan.
Loan Term: The duration of the loan. While longer terms (e.g., 72 or 84 months) lower your monthly payment, they increase the total interest paid and put you at risk of being "upside-down" on the loan longer.
Example Calculation
Imagine you are buying a new sedan for $28,000. You have saved $4,000 for a down payment and have an old car with a trade-in value of $2,000. Your credit score secures you an interest rate of 4.5% APR, and you choose a standard 60-month (5-year) term.
In this scenario, your loan principal would be $22,000 ($28,000 – $4,000 – $2,000). Using the calculator above, your estimated monthly payment would be approximately $410.15, and you would pay roughly $2,609 in total interest over the five years.