function calculateRental() {
// Retrieve inputs
var price = parseFloat(document.getElementById('purchasePrice').value);
var downPercent = parseFloat(document.getElementById('downPayment').value);
var rate = parseFloat(document.getElementById('interestRate').value);
var term = parseFloat(document.getElementById('loanTerm').value);
var rent = parseFloat(document.getElementById('monthlyRent').value);
var tax = parseFloat(document.getElementById('annualTax').value);
var insurance = parseFloat(document.getElementById('annualInsurance').value);
var vacancyP = parseFloat(document.getElementById('vacancyRate').value);
var mgmtP = parseFloat(document.getElementById('managementRate').value);
var repairP = parseFloat(document.getElementById('repairRate').value);
// Validation
if (isNaN(price) || isNaN(rent) || isNaN(term)) {
alert("Please enter valid numbers for Price, Rent, and Term.");
return;
}
// 1. Calculate Mortgage
var downPaymentAmount = price * (downPercent / 100);
var loanAmount = price – downPaymentAmount;
var monthlyRate = (rate / 100) / 12;
var totalMonths = term * 12;
var mortgagePayment = 0;
if (rate === 0) {
mortgagePayment = loanAmount / totalMonths;
} else {
mortgagePayment = loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, totalMonths)) / (Math.pow(1 + monthlyRate, totalMonths) – 1);
}
// 2. Calculate Monthly Operating Expenses
var monthlyTax = tax / 12;
var monthlyIns = insurance / 12;
var vacancyCost = rent * (vacancyP / 100);
var mgmtCost = rent * (mgmtP / 100);
var repairCost = rent * (repairP / 100);
var totalOpExpenses = monthlyTax + monthlyIns + vacancyCost + mgmtCost + repairCost;
var totalMonthlyOutflow = totalOpExpenses + mortgagePayment;
// 3. Cash Flow
var monthlyCashFlow = rent – totalMonthlyOutflow;
var annualCashFlow = monthlyCashFlow * 12;
// 4. NOI (Net Operating Income)
// NOI is Gross Income – Operating Expenses (Excluding Debt Service)
var annualOpExpenses = totalOpExpenses * 12;
var noi = (rent * 12) – annualOpExpenses;
// 5. Returns
var capRate = (noi / price) * 100;
// Cash on Cash = Annual Cash Flow / Total Cash Invested
// For simplicity, we assume closing costs are roughly 3% of purchase price, plus down payment.
var closingCosts = price * 0.03;
var totalCashInvested = downPaymentAmount + closingCosts;
var cashOnCash = (annualCashFlow / totalCashInvested) * 100;
// Display Formatting
var fmtMoney = new Intl.NumberFormat('en-US', { style: 'currency', currency: 'USD' });
var fmtPercent = new Intl.NumberFormat('en-US', { style: 'percent', minimumFractionDigits: 2, maximumFractionDigits: 2 });
document.getElementById('resIncome').innerText = fmtMoney.format(rent);
document.getElementById('resMortgage').innerText = fmtMoney.format(mortgagePayment);
document.getElementById('resExpenses').innerText = fmtMoney.format(totalOpExpenses);
var cashFlowEl = document.getElementById('resCashFlow');
cashFlowEl.innerText = fmtMoney.format(monthlyCashFlow);
if (monthlyCashFlow < 0) {
cashFlowEl.classList.add('negative');
} else {
cashFlowEl.classList.remove('negative');
}
document.getElementById('resNOI').innerText = fmtMoney.format(noi);
document.getElementById('resCapRate').innerText = capRate.toFixed(2) + "%";
var cocEl = document.getElementById('resCashOnCash');
cocEl.innerText = cashOnCash.toFixed(2) + "%";
if (cashOnCash < 0) {
cocEl.classList.add('negative');
} else {
cocEl.classList.remove('negative');
}
document.getElementById('resultsArea').style.display = 'block';
}
Mastering Real Estate Investment: Understanding Rental Property Cash Flow
Investing in rental properties is one of the most reliable ways to build long-term wealth. However, success isn't guaranteed just by buying a property. The difference between a profitable asset and a financial burden lies in the numbers. Using a comprehensive Rental Property Cash Flow Calculator is essential for evaluating potential deals accurately.
What is Positive Cash Flow?
Positive cash flow occurs when a property's gross monthly income exceeds all of its monthly expenses. These expenses aren't just the mortgage payment; they include taxes, insurance, maintenance, vacancy reserves, and property management fees. Positive cash flow ensures the property pays for itself and provides you with passive income.
Key Metrics Explained
NOI (Net Operating Income): This represents the annual profitability of the property before factoring in financing costs (mortgage). It is calculated by subtracting operating expenses from gross income. It is a pure measure of the asset's performance.
Cap Rate (Capitalization Rate): Calculated as NOI / Purchase Price, this percentage allows you to compare the profitability of different properties regardless of how they are financed. A higher cap rate generally indicates a better return, though often with higher risk.
Cash on Cash Return: This is arguably the most important metric for investors using leverage (loans). It measures the annual cash flow relative to the actual cash you invested (down payment + closing costs). It answers the question: "What is the return on the actual dollars I put into this deal?"
Estimating Expenses Accurately
New investors often overestimate cash flow by underestimating expenses. A common rule of thumb is the 50% Rule, which suggests that operating expenses (excluding mortgage) will average about 50% of the gross rent over time. While our calculator allows for specific inputs, always ensure you budget for:
Vacancy: Even in hot markets, tenants move out. Budgeting 5-8% helps cover months without rent.
Repairs & CapEx: Roofs leak and water heaters break. Setting aside 5-10% ensures you aren't paying out of pocket when major repairs arise.
Management: Even if you self-manage, accounting for an 8-10% management fee ensures the deal still works if you eventually hire a professional.
How to Use This Calculator
Enter the purchase price and loan details to determine your mortgage obligation. Then, input your projected rental income and estimated annual expenses. The calculator will break down your monthly inflow vs. outflow and provide the critical ROI metrics needed to make an informed investment decision.