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Monthly Payment:–
Total Loan Amount:–
Total Interest Paid:–
Total Cost (w/ Tax & Interest):–
Payoff Date:–
Understanding Your Car Loan Payment
Buying a car is one of the most significant financial decisions many people make, second only to purchasing a home. Using this Car Loan Amortization Calculator helps you look beyond the sticker price to understand the true monthly impact on your budget.
Key Factors That Affect Your Auto Loan
When calculating your car payments, several specific variables play a crucial role in determining how much you will pay over the life of the loan:
Vehicle Price & Sales Tax: The base price of the car plus your state's sales tax forms the gross cost. Don't forget that taxes are usually rolled into the loan if not paid upfront.
Down Payment & Trade-in: Money put down upfront or the value of your old car reduces the principal amount you need to borrow. A larger down payment significantly lowers both your monthly payment and total interest paid.
Interest Rate (APR): This is the cost of borrowing money. Rates vary based on your credit score, the vehicle's age (new vs. used), and the lender. Even a 1% difference can save or cost you hundreds of dollars over a 5-year term.
Loan Term: Common terms range from 36 to 72 months (3 to 6 years). While a longer term lowers your monthly payment, it increases the total interest you pay and keeps you in debt longer.
How the Formula Works
Car loans typically use a standard amortization formula. The calculator determines your monthly payment so that by the end of the term, both the principal and the accrued interest are paid off completely. The formula adjusts so that in the early months, a higher portion of your payment goes toward interest, while in later months, more goes toward the principal.
Tips for Getting the Best Deal
Before heading to the dealership, check your credit score and consider getting pre-approved by a bank or credit union. Dealership financing can be convenient, but having a pre-approval gives you leverage to negotiate a better interest rate. Additionally, try to keep your loan term to 60 months or less to avoid "going upside down" on your loan, where you owe more than the car is worth.
function calculateAutoLoan() {
// Clear previous error states
var errorDiv = document.getElementById("errorMessage");
var resultsDiv = document.getElementById("results-area");
errorDiv.style.display = "none";
// Get Input Values
var price = parseFloat(document.getElementById("vehiclePrice").value);
var taxRate = parseFloat(document.getElementById("salesTax").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var tradeIn = parseFloat(document.getElementById("tradeInValue").value);
var interestRate = parseFloat(document.getElementById("interestRate").value);
var months = parseFloat(document.getElementById("loanTerm").value);
// Validation logic
if (isNaN(price) || isNaN(taxRate) || isNaN(downPayment) ||
isNaN(tradeIn) || isNaN(interestRate) || isNaN(months) || months <= 0) {
errorDiv.style.display = "block";
resultsDiv.style.display = "none";
return;
}
// Calculate Tax Amount
var taxAmount = price * (taxRate / 100);
// Calculate Net Loan Amount
// Loan Amount = (Price + Tax) – (Down Payment + Trade In)
var totalCostBeforeFinance = price + taxAmount;
var deductions = downPayment + tradeIn;
var loanPrincipal = totalCostBeforeFinance – deductions;
if (loanPrincipal <= 0) {
// If down payment covers the car, no loan needed
document.getElementById("monthlyPaymentResult").innerHTML = "$0.00";
document.getElementById("loanAmountResult").innerHTML = "$0.00";
document.getElementById("totalInterestResult").innerHTML = "$0.00";
document.getElementById("totalCostResult").innerHTML = "$" + totalCostBeforeFinance.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("payoffDateResult").innerHTML = "N/A";
resultsDiv.style.display = "block";
return;
}
// Calculate Monthly Payment
// Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
// i = monthly interest rate (APR / 100 / 12)
var monthlyRate = (interestRate / 100) / 12;
var monthlyPayment = 0;
var totalInterest = 0;
var totalPaid = 0;
if (monthlyRate === 0) {
// 0% interest case
monthlyPayment = loanPrincipal / months;
totalInterest = 0;
totalPaid = loanPrincipal;
} else {
// Standard compound interest
var x = Math.pow(1 + monthlyRate, months);
monthlyPayment = (loanPrincipal * x * monthlyRate) / (x – 1);
totalPaid = monthlyPayment * months;
totalInterest = totalPaid – loanPrincipal;
}
var totalCostOfCar = totalCostBeforeFinance + totalInterest;
// Calculate Payoff Date
var today = new Date();
today.setMonth(today.getMonth() + months);
var options = { month: 'long', year: 'numeric' };
var payoffDateString = today.toLocaleDateString("en-US", options);
// Display Results
document.getElementById("monthlyPaymentResult").innerHTML = "$" + monthlyPayment.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("loanAmountResult").innerHTML = "$" + loanPrincipal.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("totalInterestResult").innerHTML = "$" + totalInterest.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("totalCostResult").innerHTML = "$" + totalCostOfCar.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("payoffDateResult").innerHTML = payoffDateString;
resultsDiv.style.display = "block";
}