function calculateROI() {
// 1. Get Inputs
var price = parseFloat(document.getElementById('purchasePrice').value);
var downPct = parseFloat(document.getElementById('downPayment').value);
var rate = parseFloat(document.getElementById('interestRate').value);
var term = parseFloat(document.getElementById('loanTerm').value);
var closingCosts = parseFloat(document.getElementById('closingCosts').value);
var monthlyRent = parseFloat(document.getElementById('monthlyRent').value);
var annualTax = parseFloat(document.getElementById('propertyTax').value);
var annualIns = parseFloat(document.getElementById('insurance').value);
var annualMaint = parseFloat(document.getElementById('maintenance').value);
var monthlyOther = parseFloat(document.getElementById('otherExpenses').value);
// 2. Validation
if (isNaN(price) || isNaN(monthlyRent) || isNaN(downPct) || isNaN(rate) || isNaN(term)) {
alert("Please fill in all required fields (Price, Down Payment, Rate, Term, Rent) with valid numbers.");
return;
}
// Default 0 for optional empty fields
if (isNaN(closingCosts)) closingCosts = 0;
if (isNaN(annualTax)) annualTax = 0;
if (isNaN(annualIns)) annualIns = 0;
if (isNaN(annualMaint)) annualMaint = 0;
if (isNaN(monthlyOther)) monthlyOther = 0;
// 3. Calculations
var downPaymentAmount = price * (downPct / 100);
var loanAmount = price – downPaymentAmount;
var monthlyRate = rate / 100 / 12;
var numPayments = term * 12;
// Mortgage Payment Calculation (Principal & Interest)
var monthlyMortgage = 0;
if (rate === 0) {
monthlyMortgage = loanAmount / numPayments;
} else {
monthlyMortgage = loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, numPayments)) / (Math.pow(1 + monthlyRate, numPayments) – 1);
}
// Expenses Calculation
var monthlyTax = annualTax / 12;
var monthlyIns = annualIns / 12;
var monthlyMaint = annualMaint / 12;
var totalMonthlyOperatingExpenses = monthlyTax + monthlyIns + monthlyMaint + monthlyOther;
var totalMonthlyExpenses = monthlyMortgage + totalMonthlyOperatingExpenses;
// Income Calculation
var monthlyCashFlow = monthlyRent – totalMonthlyExpenses;
var annualCashFlow = monthlyCashFlow * 12;
// ROI Metrics
var totalCashInvested = downPaymentAmount + closingCosts;
var cashOnCash = (annualCashFlow / totalCashInvested) * 100;
// Net Operating Income (NOI) = Annual Income – Annual Operating Expenses (Excluding Mortgage)
var annualOperatingExpenses = totalMonthlyOperatingExpenses * 12;
var annualIncome = monthlyRent * 12;
var noi = annualIncome – annualOperatingExpenses;
var capRate = (noi / price) * 100;
// 4. Update UI
document.getElementById('resMortgage').innerText = "$" + monthlyMortgage.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resTotalExpenses').innerText = "$" + totalMonthlyExpenses.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resNOI').innerText = "$" + noi.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
var cashFlowEl = document.getElementById('resMonthlyCashFlow');
cashFlowEl.innerText = "$" + monthlyCashFlow.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
cashFlowEl.style.color = monthlyCashFlow >= 0 ? '#27ae60' : '#c0392b';
var cocEl = document.getElementById('resCoC');
cocEl.innerText = cashOnCash.toFixed(2) + "%";
cocEl.style.color = cashOnCash >= 0 ? '#27ae60' : '#c0392b';
document.getElementById('resCapRate').innerText = capRate.toFixed(2) + "%";
// Show results
document.getElementById('resultArea').style.display = 'block';
}
Understanding Rental Property ROI
Investing in rental real estate is one of the most powerful ways to build wealth, but simply buying a property doesn't guarantee a profit. To be a successful investor, you must analyze the numbers before signing a contract. This Rental Property ROI Calculator helps you evaluate the potential profitability of an investment by calculating key metrics like Cash Flow, Cash on Cash Return, and Cap Rate.
Key Metrics Explained
1. Monthly Cash Flow
Cash flow is the profit you take home each month after all expenses are paid. It is calculated as:
Total Income: Usually the monthly rent.
Minus Expenses: Mortgage payments, taxes, insurance, maintenance, and HOA fees.
Positive cash flow ensures that the property pays for itself and provides passive income. Negative cash flow means you are losing money every month to hold the property.
2. Cash on Cash Return (CoC)
Cash on Cash Return measures the percentage of your initial cash investment that is returned to you as annual cash flow. It is widely considered the most important metric for rental investors because it reflects the efficiency of your capital.
For example, if you invest $50,000 (down payment + closing costs) and the property generates $5,000 in positive cash flow per year, your Cash on Cash return is 10%.
3. Cap Rate (Capitalization Rate)
The Cap Rate measures the natural rate of return on an investment property assuming it was bought with all cash (no loan). It helps compare the profitability of different properties regardless of how they are financed.
Formula: (Net Operating Income / Purchase Price) × 100
Net Operating Income (NOI) is the revenue left over after operating expenses (taxes, insurance, repairs) but before paying the mortgage.
Tips for Improving Your ROI
If your calculation shows a low or negative return, consider these strategies to improve the numbers:
Increase Rent: Can minor cosmetic upgrades allow you to charge more?
Lower Expenses: Shop around for cheaper insurance or self-manage the property to save on management fees.
Negotiate Price: A lower purchase price reduces your mortgage payment and increases your immediate equity.
Decrease Interest Rate: Shopping for lenders or buying points can significantly lower monthly mortgage costs.
Why Use a Rental Property Calculator?
Real estate investing involves moving parts. A small change in interest rates, property taxes, or vacancy estimates can turn a good deal into a bad one. By using this calculator, you can "stress test" your investment against different scenarios to ensure you make a data-driven decision.