function calculateAutoLease() {
// 1. Get input values
var msrp = parseFloat(document.getElementById('alrc_msrp').value);
var sellingPrice = parseFloat(document.getElementById('alrc_neg_price').value);
var downPayment = parseFloat(document.getElementById('alrc_down_payment').value);
var residualPct = parseFloat(document.getElementById('alrc_residual').value);
var moneyFactor = parseFloat(document.getElementById('alrc_money_factor').value);
var term = parseFloat(document.getElementById('alrc_term').value);
var taxRate = parseFloat(document.getElementById('alrc_tax').value);
// 2. Validate inputs
if (isNaN(msrp) || isNaN(sellingPrice) || isNaN(residualPct) || isNaN(moneyFactor) || isNaN(term)) {
alert("Please fill in all required fields (MSRP, Selling Price, Residual %, Money Factor, Term) with valid numbers.");
return;
}
// Handle optional fields defaults
if (isNaN(downPayment)) downPayment = 0;
if (isNaN(taxRate)) taxRate = 0;
// 3. Perform Calculations
// A. Net Capitalized Cost = Negotiated Price – Down Payment
var netCapCost = sellingPrice – downPayment;
// B. Residual Value Amount = MSRP * (Residual % / 100)
var residualValue = msrp * (residualPct / 100);
// C. Monthly Depreciation Fee = (Net Cap Cost – Residual Value) / Term
// Note: If Net Cap Cost is lower than Residual, depreciation is zero (unlikely but possible with huge down payment)
var depreciationFee = (netCapCost – residualValue) / term;
if (depreciationFee < 0) depreciationFee = 0;
// D. Monthly Finance Fee (Rent Charge) = (Net Cap Cost + Residual Value) * Money Factor
var rentCharge = (netCapCost + residualValue) * moneyFactor;
// E. Base Monthly Payment
var basePayment = depreciationFee + rentCharge;
// F. Monthly Tax = Base Payment * (Tax Rate / 100)
// Note: Some states tax the full vehicle price upfront. This calculator assumes tax on monthly payment flows.
var monthlyTax = basePayment * (taxRate / 100);
// G. Total Monthly Payment
var totalPayment = basePayment + monthlyTax;
// 4. Update Result Elements
document.getElementById('res_net_cap').innerText = "$" + netCapCost.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('res_residual_amt').innerText = "$" + residualValue.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('res_depreciation').innerText = "$" + depreciationFee.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('res_rent_charge').innerText = "$" + rentCharge.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('res_tax').innerText = "$" + monthlyTax.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('res_total').innerText = "$" + totalPayment.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
// Show result box
document.getElementById('alrc_result').style.display = "block";
}
Understanding the Auto Lease Rate Calculator
Leasing a vehicle involves a different set of mathematical rules than buying one with a traditional auto loan. While a loan is based on the total principal and an interest rate (APR), a lease is primarily based on the vehicle's depreciation and the "Money Factor." This tool allows you to input specific lease variables to estimate your true monthly payment accurately.
Key Lease Terms Explained
1. Capitalized Cost (Cap Cost)
This is essentially the price of the vehicle. Just like buying a car, you should negotiate this price. The "Gross Capitalized Cost" is the negotiated price plus any fees. The "Net Capitalized Cost" is the gross cost minus any down payments, trade-ins, or rebates (Cap Cost Reduction).
2. Residual Value
The residual value is the estimated value of the car at the end of the lease term. It is determined by the leasing bank and is usually expressed as a percentage of the MSRP (not the negotiated price). A higher residual value generally leads to lower monthly payments because you are paying for less depreciation.
3. Money Factor (MF)
This is the lease equivalent of an interest rate. It represents the cost of borrowing the money tied up in the car's value. To convert a Money Factor to an approximate APR (Annual Percentage Rate), multiply the Money Factor by 2400. For example, a Money Factor of 0.00125 is roughly equivalent to a 3% APR.
4. The Rent Charge
Unlike a standard loan where interest is charged on the remaining balance, the lease finance fee (rent charge) is calculated using a unique formula: (Net Cap Cost + Residual Value) × Money Factor. This fee is paid monthly along with the depreciation.
How the Monthly Payment is Calculated
Your lease payment consists of three main parts:
Depreciation Fee: This pays for the value the car loses during your possession. It is calculated as (Net Cap Cost – Residual Value) ÷ Lease Term.
Finance Fee: This is the interest paid to the leasing company.
Sales Tax: In most states, sales tax is applied to the monthly payment rather than the total price of the car.
Tips for Lowering Your Lease Rate
To get the best deal, focus on negotiating the Selling Price of the car first. Many buyers make the mistake of negotiating the monthly payment directly, which allows dealers to manipulate the Money Factor or extend the term to hit a target number while keeping the profit high. Always ask for the "base Money Factor" to ensure the dealer isn't marking up the rate for extra profit.