Purchasing a new vehicle is a significant financial decision, and understanding how your trade-in impacts your auto loan is crucial. This calculator helps you estimate your monthly car payment by factoring in the vehicle's price, your cash down payment, and the value of your trade-in vehicle.
How it Works:
The core of this calculation is determining the actual amount you need to finance. Here's the breakdown:
Vehicle Price: The sticker price or negotiated price of the car you wish to purchase.
Cash Down Payment: The amount of money you pay upfront directly from your pocket.
Trade-In Value: The amount your current vehicle is worth and will be applied as a credit towards the new vehicle. This value is deducted from the total cost.
The Loan Amount is calculated as: Vehicle Price - Cash Down Payment - Trade-In Value.
Once the loan amount is determined, the calculator uses a standard auto loan formula to estimate the monthly payment based on the loan term (in months) and the annual interest rate. The formula for the monthly payment (M) is:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
Where:
P = Principal Loan Amount (the amount you need to borrow)
n = Total Number of Payments (Loan Term in Months)
This calculator also provides insights into the total interest you'll pay over the life of the loan and the total amount repaid.
Why Use This Calculator?
Budgeting: Get a realistic estimate of your monthly car expenses.
Negotiation Power: Understand how much you can afford and the impact of your down payment and trade-in on your overall cost.
Loan Comparison: Evaluate different loan offers by inputting their respective interest rates and terms.
Financial Planning: Make informed decisions about vehicle purchases and manage your finances effectively.
Remember, this is an estimate. Actual loan terms and payments may vary based on lender approval, specific loan products, taxes, fees, and other charges. Always consult with your auto dealer or financial institution for precise figures.
function calculateAutoLoan() {
var vehiclePrice = parseFloat(document.getElementById("vehiclePrice").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var tradeInValue = parseFloat(document.getElementById("tradeInValue").value);
var loanTerm = parseInt(document.getElementById("loanTerm").value);
var annualInterestRate = parseFloat(document.getElementById("annualInterestRate").value);
var errorMessageDiv = document.getElementById("errorMessage");
var resultMonthlyPaymentDiv = document.getElementById("result-monthly-payment");
var detailLoanAmountSpan = document.getElementById("detail-loan-amount");
var detailTotalInterestSpan = document.getElementById("detail-total-interest");
var detailTotalRepaidSpan = document.getElementById("detail-total-repaid");
errorMessageDiv.textContent = "; // Clear previous errors
// Input validation
if (isNaN(vehiclePrice) || vehiclePrice <= 0) {
errorMessageDiv.textContent = "Please enter a valid Vehicle Price.";
return;
}
if (isNaN(downPayment) || downPayment < 0) {
errorMessageDiv.textContent = "Please enter a valid Cash Down Payment (cannot be negative).";
return;
}
if (isNaN(tradeInValue) || tradeInValue < 0) {
errorMessageDiv.textContent = "Please enter a valid Trade-In Value (cannot be negative).";
return;
}
if (isNaN(loanTerm) || loanTerm <= 0) {
errorMessageDiv.textContent = "Please enter a valid Loan Term in months.";
return;
}
if (isNaN(annualInterestRate) || annualInterestRate < 0) {
errorMessageDiv.textContent = "Please enter a valid Annual Interest Rate (cannot be negative).";
return;
}
var loanAmount = vehiclePrice – downPayment – tradeInValue;
if (loanAmount 0 && monthlyInterestRate > 0) {
// Standard Amortization Formula
var numerator = monthlyInterestRate * Math.pow(1 + monthlyInterestRate, loanTerm);
var denominator = Math.pow(1 + monthlyInterestRate, loanTerm) – 1;
monthlyPayment = loanAmount * (numerator / denominator);
totalRepaid = monthlyPayment * loanTerm;
totalInterestPaid = totalRepaid – loanAmount;
} else if (loanAmount > 0 && monthlyInterestRate === 0) {
// Simple interest if rate is 0
monthlyPayment = loanAmount / loanTerm;
totalInterestPaid = 0;
totalRepaid = loanAmount;
} else {
monthlyPayment = 0;
totalInterestPaid = 0;
totalRepaid = loanAmount > 0 ? loanAmount : 0; // If loanAmount is 0 or less, total repaid is 0.
}
// Format results for display
resultMonthlyPaymentDiv.textContent = '$' + monthlyPayment.toFixed(2);
detailLoanAmountSpan.textContent = '$' + loanAmount.toFixed(2);
detailTotalInterestSpan.textContent = '$' + totalInterestPaid.toFixed(2);
detailTotalRepaidSpan.textContent = '$' + totalRepaid.toFixed(2);
// Show result section
document.getElementById("result").style.display = 'block';
}