function calculateComparison() {
var price = parseFloat(document.getElementById('vehiclePrice').value) || 0;
var taxRate = (parseFloat(document.getElementById('salesTax').value) || 0) / 100;
// Lease Logic
var lDown = parseFloat(document.getElementById('leaseDown').value) || 0;
var lTerm = parseFloat(document.getElementById('leaseTerm').value) || 0;
var mFactor = parseFloat(document.getElementById('moneyFactor').value) || 0;
var residual = parseFloat(document.getElementById('residualValue').value) || 0;
var capCost = price – lDown;
var monthlyDepreciation = (capCost – residual) / lTerm;
var monthlyRentCharge = (capCost + residual) * mFactor;
var leaseMonthly = (monthlyDepreciation + monthlyRentCharge) * (1 + taxRate);
var totalLeaseCost = (leaseMonthly * lTerm) + lDown;
// Buy Logic
var bDown = parseFloat(document.getElementById('buyDown').value) || 0;
var bTerm = parseFloat(document.getElementById('buyTerm').value) || 0;
var bAPR = (parseFloat(document.getElementById('buyAPR').value) || 0) / 100;
var loanAmount = (price * (1 + taxRate)) – bDown;
var monthlyInt = bAPR / 12;
var buyMonthly = 0;
if (monthlyInt > 0) {
buyMonthly = loanAmount * (monthlyInt * Math.pow(1 + monthlyInt, bTerm)) / (Math.pow(1 + monthlyInt, bTerm) – 1);
} else {
buyMonthly = loanAmount / bTerm;
}
var totalBuyCost = (buyMonthly * bTerm) + bDown;
// Display
document.getElementById('resultsArea').style.display = 'block';
document.getElementById('leaseResult').innerText = '$' + leaseMonthly.toFixed(2);
document.getElementById('buyResult').innerText = '$' + buyMonthly.toFixed(2);
document.getElementById('leaseTotal').innerText = 'Total cost over ' + lTerm + ' months: $' + totalLeaseCost.toLocaleString(undefined, {minimumFractionDigits: 2});
document.getElementById('buyTotal').innerText = 'Total cost over ' + bTerm + ' months: $' + totalBuyCost.toLocaleString(undefined, {minimumFractionDigits: 2});
var verdict = document.getElementById('verdict');
if (leaseMonthly < buyMonthly) {
verdict.style.backgroundColor = '#ebf8ff';
verdict.style.color = '#2b6cb0';
verdict.innerText = 'Leasing saves you $' + (buyMonthly – leaseMonthly).toFixed(2) + ' per month in cash flow.';
} else {
verdict.style.backgroundColor = '#f0fff4';
verdict.style.color = '#2f855a';
verdict.innerText = 'Financing is competitive but builds equity. Leasing costs $' + (leaseMonthly – buyMonthly).toFixed(2) + ' more monthly.';
}
}
Understanding Car Lease vs. Buy Math
Deciding whether to lease or buy a car is one of the most significant financial decisions for many households. While both options put you behind the wheel of a new vehicle, the underlying financial structures are vastly different. This calculator helps you break down the monthly commitment and total out-of-pocket costs for both scenarios.
How Leasing Costs are Calculated
A lease payment is primarily composed of two parts: Depreciation and the Money Factor.
Depreciation: You pay for the portion of the car's value you "use up." If a $35,000 car is worth $21,000 after three years, your depreciation cost is $14,000.
Money Factor: This is essentially the interest rate on a lease. To find the equivalent APR, multiply the money factor by 2,400. (e.g., 0.0015 * 2400 = 3.6% APR).
Residual Value: This is the predicted value of the car at the end of the lease. A higher residual value usually results in a lower monthly payment.
The Financing (Buying) Advantage
When you finance a car, you are borrowing the full purchase price (plus tax) minus your down payment. While the monthly payments are typically higher than a lease, you are building equity. At the end of the loan term, you own the vehicle outright, which can then be sold or traded in toward your next purchase.
Example Comparison Scenario
Let's look at a realistic example for a $40,000 SUV:
Feature
36-Month Lease
60-Month Loan
Down Payment
$2,500
$5,000
Monthly Payment
~$485
~$680
End of Term
Return car (No equity)
Own car (Full equity)
Which Should You Choose?
Lease if: You enjoy driving a new car every 3 years, want lower monthly payments, and stay within standard mileage limits (usually 10,000–12,000 miles/year).
Buy if: You plan to keep the car for 5+ years, drive long distances, or want to eventually live without a monthly car payment.