This calculator helps you estimate your monthly payments, total amount paid, and total interest for an auto loan, based on the car's price, your down payment, the loan term, and the annual interest rate. The calculations are based on the standard amortization formula used for most loans.
How the Calculation Works
The core of the auto loan calculation is the monthly payment formula:
$ M = P \left[ \frac{r(1+r)^n}{(1+r)^n – 1} \right] $
Where:
$M$ = Your monthly loan payment
$P$ = The principal loan amount (Car Price – Down Payment)
$n$ = The total number of payments (Loan Term in Years * 12)
Once the monthly payment ($M$) is calculated, we can determine the other figures:
Total Amount Paid = Monthly Payment ($M$) * Total Number of Payments ($n$)
Total Interest Paid = Total Amount Paid – Principal Loan Amount ($P$)
Key Inputs Explained
Car Price: The total sticker price of the vehicle you intend to purchase.
Down Payment: The amount of money you pay upfront. This reduces the principal loan amount, thereby lowering your monthly payments and total interest paid.
Loan Term (Years): The duration over which you agree to repay the loan. Longer terms generally result in lower monthly payments but higher overall interest paid.
Interest Rate (%): The annual percentage rate (APR) charged by the lender. A lower interest rate means you pay less in interest over the life of the loan.
Why Use an Auto Loan Calculator?
An auto loan calculator like this one is a vital tool for financial planning when buying a car. It allows you to:
Budget Effectively: Understand how much car you can afford by experimenting with different prices and down payments to meet your desired monthly payment.
Compare Offers: Evaluate different loan offers from various lenders. Even a small difference in interest rate or loan term can have a significant impact on your total cost.
Negotiate Better: Knowing your estimated payments can give you confidence at the dealership. You can focus on negotiating the car's price and financing terms separately.
Plan for Savings: See how increasing your down payment or choosing a shorter loan term can save you money on interest.
Remember, the results from this calculator are estimates. Actual loan terms and payments may vary based on lender fees, your credit score, and specific loan agreements. Always review the official loan documents carefully.
function calculateLoan() {
var carPrice = parseFloat(document.getElementById("carPrice").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var loanTermYears = parseFloat(document.getElementById("loanTerm").value); // Use the value from the hidden input
var annualInterestRate = parseFloat(document.getElementById("interestRate").value); // Use the value from the hidden input
// Input validation
if (isNaN(carPrice) || carPrice <= 0) {
alert("Please enter a valid car price.");
return;
}
if (isNaN(downPayment) || downPayment < 0) {
alert("Please enter a valid down payment.");
return;
}
if (isNaN(loanTermYears) || loanTermYears <= 0) {
alert("Please enter a valid loan term in years.");
return;
}
if (isNaN(annualInterestRate) || annualInterestRate < 0) {
alert("Please enter a valid annual interest rate.");
return;
}
var loanAmount = carPrice – downPayment;
if (loanAmount <= 0) {
document.getElementById("result").innerHTML = "
Your Estimated Auto Loan Details
$0.00Total Paid: $" + carPrice.toFixed(2) + "Total Interest: $0.00";
return;
}
var monthlyInterestRate = annualInterestRate / 100 / 12;
var numberOfPayments = loanTermYears * 12;
var monthlyPayment = 0;
if (monthlyInterestRate > 0) {
monthlyPayment = loanAmount * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1);
} else {
monthlyPayment = loanAmount / numberOfPayments;
}
var totalPaid = monthlyPayment * numberOfPayments;
var totalInterest = totalPaid – loanAmount;
// Format results
var formattedMonthlyPayment = "$" + monthlyPayment.toFixed(2);
var formattedTotalPaid = "$" + totalPaid.toFixed(2);
var formattedTotalInterest = "$" + totalInterest.toFixed(2);
document.getElementById("result").innerHTML = "
Your Estimated Auto Loan Details
" + formattedMonthlyPayment + "Total Paid: " + formattedTotalPaid + "Total Interest: " + formattedTotalInterest + "";
}
// Update slider display on initial load
document.addEventListener('DOMContentLoaded', function() {
var loanTermSlider = document.getElementById('loanTerm');
var loanTermSpan = document.getElementById('loanTermValue');
loanTermSpan.innerText = loanTermSlider.value + ' years';
loanTermSlider.oninput = function() {
loanTermSpan.innerText = this.value + ' years';
// Update the hidden input value
document.getElementById('loanTerm').value = this.value;
};
var interestRateSlider = document.getElementById('interestRate');
var interestRateSpan = document.getElementById('interestRateValue');
interestRateSpan.innerText = interestRateSlider.value + '%';
interestRateSlider.oninput = function() {
interestRateSpan.innerText = this.value + '%';
// Update the hidden input value
document.getElementById('interestRate').value = this.value;
};
// Trigger calculation on load if default values are set
calculateLoan();
});