Please enter valid positive numbers for all fields.
Estimated Monthly Payment:$0.00
Total Loan Amount:$0.00
Total Interest:$0.00
Total Cost (w/ Tax & Interest):$0.00
Payoff Date:–
Understanding Your Auto Loan
Purchasing a vehicle is one of the largest financial commitments most people make, second only to buying a home. This Auto Loan Calculator helps you estimate your monthly payments and total interest costs, empowering you to negotiate better terms at the dealership.
How the Calculation Works
To determine your monthly payment, this tool considers several critical factors specific to car buying:
Vehicle Price: The negotiated sticker price of the car.
Trade-in & Down Payment: Equity you are putting in upfront reduces the principal loan amount.
Sales Tax: Unlike mortgages, sales tax on vehicles is often rolled into the loan amount. We calculate this based on the vehicle price minus the trade-in value (depending on state laws, but calculated generally here).
APR (Annual Percentage Rate): Your credit score significantly impacts this rate. A lower rate can save you thousands over the life of the loan.
The Impact of Loan Terms
While a 72 or 84-month loan might offer a lower monthly payment, it significantly increases the total interest you pay. For example, extending a $30,000 loan from 60 months to 84 months at 5% APR might lower your payment by $100/month, but it will cost you an additional $1,500 in interest.
Tips for Using This Calculator
Use the "Trade-in Value" field to see how much your old car can reduce your new payments. If you are unsure of your local sales tax, the national average is roughly 6-7%. Remember to factor in insurance and maintenance costs which are not included in this loan calculation.
function calculateCarLoan() {
// Get input values
var price = parseFloat(document.getElementById("vehiclePrice").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var tradeIn = parseFloat(document.getElementById("tradeInValue").value);
var rate = parseFloat(document.getElementById("interestRate").value);
var months = parseInt(document.getElementById("loanTerm").value);
var taxRate = parseFloat(document.getElementById("salesTax").value);
// Handle empty inputs by defaulting to 0
if (isNaN(price)) price = 0;
if (isNaN(downPayment)) downPayment = 0;
if (isNaN(tradeIn)) tradeIn = 0;
if (isNaN(rate)) rate = 0;
if (isNaN(taxRate)) taxRate = 0;
// Basic Validation
if (price <= 0 || months <= 0) {
document.getElementById("error-message").style.display = "block";
document.getElementById("error-message").innerText = "Please enter a valid Vehicle Price and Loan Term.";
document.getElementById("results").style.display = "none";
return;
}
document.getElementById("error-message").style.display = "none";
// Calculate Taxable Amount (Price – TradeIn) – simplified logic
// Note: Some states tax before trade-in, some after. We will assume after trade-in for this generic tool.
var taxableAmount = price – tradeIn;
if (taxableAmount < 0) taxableAmount = 0;
var taxAmount = taxableAmount * (taxRate / 100);
// Calculate Loan Principal
// Principal = Price + Tax – DownPayment – TradeIn
var loanPrincipal = price + taxAmount – downPayment – tradeIn;
if (loanPrincipal <= 0) {
// No loan needed
document.getElementById("results").style.display = "block";
document.getElementById("monthlyPayment").innerText = "$0.00";
document.getElementById("totalLoanAmount").innerText = "$0.00";
document.getElementById("totalInterest").innerText = "$0.00";
document.getElementById("totalCost").innerText = "$" + (price + taxAmount).toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("payoffDate").innerText = "N/A";
return;
}
// Interest Logic
var monthlyRate = (rate / 100) / 12;
var monthlyPayment = 0;
var totalInterest = 0;
if (rate === 0) {
monthlyPayment = loanPrincipal / months;
totalInterest = 0;
} else {
// Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
monthlyPayment = loanPrincipal * (monthlyRate * Math.pow(1 + monthlyRate, months)) / (Math.pow(1 + monthlyRate, months) – 1);
totalInterest = (monthlyPayment * months) – loanPrincipal;
}
var totalCost = price + taxAmount + totalInterest;
// Calculate Payoff Date
var today = new Date();
var payoffDate = new Date(today.setMonth(today.getMonth() + months));
var options = { year: 'numeric', month: 'long' };
var dateString = payoffDate.toLocaleDateString("en-US", options);
// Display Results
document.getElementById("results").style.display = "block";
document.getElementById("monthlyPayment").innerText = "$" + monthlyPayment.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("totalLoanAmount").innerText = "$" + loanPrincipal.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("totalInterest").innerText = "$" + totalInterest.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("totalCost").innerText = "$" + totalCost.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("payoffDate").innerText = dateString;
}