Please fill in valid positive numbers for all required fields.
Estimated Monthly Payment
$0.00
Total Loan Amount:$0.00
Total Sales Tax:$0.00
Total Interest:$0.00
Total Cost (Price + Tax + Interest):$0.00
Payoff Date:—
function calculateAutoLoan() {
// 1. Get input values by ID
var priceInput = document.getElementById("vehiclePrice").value;
var downPaymentInput = document.getElementById("downPayment").value;
var tradeInInput = document.getElementById("tradeInValue").value;
var taxRateInput = document.getElementById("salesTax").value;
var interestRateInput = document.getElementById("interestRate").value;
var termInput = document.getElementById("loanTerm").value;
// 2. Parse values to floats
var price = parseFloat(priceInput);
var downPayment = parseFloat(downPaymentInput) || 0;
var tradeIn = parseFloat(tradeInInput) || 0;
var taxRate = parseFloat(taxRateInput) || 0;
var annualRate = parseFloat(interestRateInput);
var months = parseInt(termInput);
// 3. Validation
var errorMsg = document.getElementById("errorMsg");
var resultsArea = document.getElementById("resultsArea");
if (isNaN(price) || isNaN(annualRate) || isNaN(months) || price <= 0 || annualRate < 0) {
errorMsg.style.display = "block";
resultsArea.style.display = "none";
return;
} else {
errorMsg.style.display = "none";
resultsArea.style.display = "block";
}
// 4. Calculation Logic
// Calculate Tax: Generally Tax is applied to (Price – TradeIn) in many states, or just Price.
// We will assume Tax is on (Price – TradeIn) for a more accurate net cost scenario, but ensuring it doesn't go negative.
var taxableAmount = Math.max(0, price – tradeIn);
var taxAmount = taxableAmount * (taxRate / 100);
// Adjusted Price with Tax
var totalPriceWithTax = price + taxAmount;
// Loan Principal = Total Price + Tax – Down Payment – Trade In
var loanPrincipal = totalPriceWithTax – downPayment – tradeIn;
// Handle case where downpayment + tradein covers the car
if (loanPrincipal <= 0) {
document.getElementById("monthlyPaymentResult").innerHTML = "$0.00";
document.getElementById("totalLoanAmount").innerHTML = "$0.00";
document.getElementById("totalTaxAmount").innerHTML = "$" + taxAmount.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("totalInterest").innerHTML = "$0.00";
document.getElementById("totalCost").innerHTML = "$" + totalPriceWithTax.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("payoffDate").innerHTML = "Paid in Full";
return;
}
var monthlyRate = (annualRate / 100) / 12;
var monthlyPayment = 0;
var totalInterest = 0;
if (monthlyRate === 0) {
// 0% Interest case
monthlyPayment = loanPrincipal / months;
totalInterest = 0;
} else {
// Standard Amortization Formula: M = P * [ r(1+r)^n ] / [ (1+r)^n – 1 ]
var x = Math.pow(1 + monthlyRate, months);
monthlyPayment = (loanPrincipal * x * monthlyRate) / (x – 1);
totalInterest = (monthlyPayment * months) – loanPrincipal;
}
var totalCost = totalPriceWithTax + totalInterest;
// Calculate Payoff Date
var today = new Date();
today.setMonth(today.getMonth() + months);
var payoffMonthYear = today.toLocaleString('default', { month: 'short', year: 'numeric' });
// 5. Update DOM
document.getElementById("monthlyPaymentResult").innerHTML = "$" + monthlyPayment.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("totalLoanAmount").innerHTML = "$" + loanPrincipal.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("totalTaxAmount").innerHTML = "$" + taxAmount.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("totalInterest").innerHTML = "$" + totalInterest.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("totalCost").innerHTML = "$" + totalCost.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("payoffDate").innerHTML = payoffMonthYear;
}
How to Use This Auto Loan Calculator
Buying a new or used car is a significant financial commitment. This Auto Loan Calculator helps you estimate your monthly payments and understand the total cost of financing a vehicle. By inputting the vehicle price, your down payment, trade-in value, and financing terms, you can see exactly how much you'll pay each month and how much interest will accrue over the life of the loan.
Simply enter the negotiated price of the car, how much cash you are putting down, and the value of your current vehicle if you are trading it in. Don't forget to include the sales tax rate for your state, as this is often rolled into the loan amount and accrues interest.
Understanding the Key Inputs
To get the most accurate result, it helps to understand what each field represents:
Vehicle Price: The final negotiated price of the car before taxes and fees. This is not necessarily the MSRP (sticker price), but the price you agree to pay the dealer.
Down Payment: Cash you pay upfront. A larger down payment reduces the principal loan amount, which lowers your monthly payment and the total interest paid.
Trade-in Value: The amount the dealership offers for your old vehicle. This acts like a down payment, directly reducing the amount you need to borrow.
Interest Rate (APR): The Annual Percentage Rate is the cost of borrowing money. This is determined by your credit score, the lender, and current market rates. Lower is always better.
Loan Term: The length of time you have to repay the loan. Common terms are 36, 48, 60, or 72 months.
How Loan Terms Affect Your Wallet
One of the most critical decisions when financing a car is choosing the Loan Term. It is tempting to choose a longer term (like 72 or 84 months) because it results in a significantly lower monthly payment. However, this comes at a cost.
A longer loan term means you are paying interest for more years. For example, extending a loan from 60 months to 72 months might lower your payment by $50 a month, but it could cost you hundreds or even thousands more in total interest over the life of the loan. Additionally, cars depreciate quickly. With a long-term loan, you risk being "upside-down" (owing more than the car is worth) for a longer period.
The Impact of Sales Tax
Many buyers forget to factor in sales tax, which can add thousands of dollars to the total cost. In most states, sales tax is calculated on the difference between the vehicle price and your trade-in value. This calculator estimates the tax and adds it to your total loan amount if you choose to finance it.
Strategies for a Lower Monthly Payment
If the calculated monthly payment is higher than your budget allows, consider these strategies:
Increase your Down Payment: Putting more money down instantly lowers the principal.
Improve your Credit Score: A better credit score qualifies you for lower interest rates.
Choose a Cheaper Vehicle: It sounds obvious, but opting for a model with fewer features or a used car can save you significantly.
Shop for Rates: Don't just accept the dealer's financing. Check with local credit unions or banks to see if you can get a lower APR.
Use this tool to experiment with different scenarios before you head to the dealership. knowing your numbers gives you leverage in negotiations and peace of mind in your purchase.