function calculateRentalROI() {
// Clear error
document.getElementById("errorMsg").style.display = "none";
document.getElementById("results-area").style.display = "none";
// Get Input Values
var purchasePrice = parseFloat(document.getElementById("purchasePrice").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var closingCosts = parseFloat(document.getElementById("closingCosts").value);
var rehabCosts = parseFloat(document.getElementById("rehabCosts").value);
var interestRate = parseFloat(document.getElementById("interestRate").value);
var loanTerm = parseFloat(document.getElementById("loanTerm").value);
var monthlyRent = parseFloat(document.getElementById("monthlyRent").value);
var propertyTax = parseFloat(document.getElementById("propertyTax").value);
var insurance = parseFloat(document.getElementById("insurance").value);
var hoa = parseFloat(document.getElementById("hoa").value);
var maintenancePct = parseFloat(document.getElementById("maintenance").value);
var vacancyPct = parseFloat(document.getElementById("vacancy").value);
var managementPct = parseFloat(document.getElementById("management").value);
// Validation
if (isNaN(purchasePrice) || isNaN(downPayment) || isNaN(interestRate) || isNaN(monthlyRent)) {
document.getElementById("errorMsg").style.display = "block";
return;
}
// 1. Mortgage Calculation
var loanAmount = purchasePrice – downPayment;
var monthlyRate = (interestRate / 100) / 12;
var numberOfPayments = loanTerm * 12;
var mortgagePayment = 0;
if (interestRate > 0) {
mortgagePayment = loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments)) / (Math.pow(1 + monthlyRate, numberOfPayments) – 1);
} else {
mortgagePayment = loanAmount / numberOfPayments;
}
// 2. Monthly Expenses Calculation
var monthlyTax = propertyTax / 12;
var monthlyInsurance = insurance / 12;
var maintenanceCost = monthlyRent * (maintenancePct / 100);
var vacancyCost = monthlyRent * (vacancyPct / 100);
var managementCost = monthlyRent * (managementPct / 100);
var totalOperatingExpenses = monthlyTax + monthlyInsurance + hoa + maintenanceCost + vacancyCost + managementCost;
var totalExpenses = totalOperatingExpenses + mortgagePayment;
// 3. NOI & Cash Flow
var noiMonthly = monthlyRent – totalOperatingExpenses;
var noiAnnual = noiMonthly * 12;
var cashFlowMonthly = monthlyRent – totalExpenses;
var cashFlowAnnual = cashFlowMonthly * 12;
// 4. Returns
var totalCashInvested = downPayment + closingCosts + rehabCosts;
var cocReturn = 0;
if (totalCashInvested > 0) {
cocReturn = (cashFlowAnnual / totalCashInvested) * 100;
}
var capRate = 0;
if (purchasePrice > 0) {
capRate = (noiAnnual / purchasePrice) * 100; // Cap Rate usually excludes financing costs
}
// Display Results
document.getElementById("resMortgage").innerText = "$" + mortgagePayment.toLocaleString("en-US", {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("resExpenses").innerText = "$" + totalExpenses.toLocaleString("en-US", {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("resNOI").innerText = "$" + noiMonthly.toLocaleString("en-US", {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("resCashFlow").innerText = "$" + cashFlowMonthly.toLocaleString("en-US", {minimumFractionDigits: 2, maximumFractionDigits: 2});
// Color coding cash flow
if (cashFlowMonthly >= 0) {
document.getElementById("resCashFlow").style.color = "#27ae60";
} else {
document.getElementById("resCashFlow").style.color = "#c0392b";
}
document.getElementById("resCoC").innerText = cocReturn.toFixed(2) + "%";
document.getElementById("resCapRate").innerText = capRate.toFixed(2) + "%";
document.getElementById("results-area").style.display = "block";
}
Mastering Rental Property Analysis
Investing in real estate is one of the most reliable ways to build wealth, but it requires precise calculations to ensure profitability. A Rental Property Cash Flow Calculator is an essential tool for investors to evaluate a potential deal before signing any papers. By inputting specific financial variables, you can determine if a property will generate positive cash flow or become a financial burden.
What is Cash Flow in Real Estate?
Cash flow is the profit remaining after all expenses have been paid. This includes the mortgage, taxes, insurance, and operational costs like maintenance and property management.
Formula:Cash Flow = Total Monthly Rental Income – Total Monthly Expenses
Positive cash flow means the property puts money in your pocket every month, while negative cash flow implies you are losing money to hold the asset.
Key Metrics Calculated
NOI (Net Operating Income): This measures the profitability of the property excluding financing costs. It is crucial for determining the raw potential of the asset.
Cap Rate (Capitalization Rate): Calculated as NOI / Purchase Price. This percentage allows you to compare the ROI of different properties regardless of how they are financed.
Cash on Cash Return (CoC): Perhaps the most important metric for leveraged investors. It measures the annual cash flow relative to the actual cash you invested (Down Payment + Closing Costs + Rehab). A CoC return of 8-12% is often considered a solid benchmark for rental properties.
Estimating Expenses Accurately
A common mistake among new investors is underestimating expenses. When using this calculator, ensure you account for:
Vacancy: Even in hot markets, tenants move out. Allocating 5-10% of rent for vacancy ensures you have reserves for turnover periods.
Maintenance & CapEx: Roofs leak and toilets break. Setting aside 5-10% for repairs and capital expenditures protects your cash flow from sudden shocks.
Property Management: Even if you plan to self-manage, it is wise to calculate the deal with an 8-10% management fee. This ensures the deal still works if you decide to hire a professional later.
How to Use This Calculator
Start by entering the purchase price and your financing details. Be honest with your rental projections—look at comparable local listings rather than guessing. Finally, adjust your expense percentages based on the age and condition of the property. Older homes generally require higher maintenance reserves (10-15%) compared to new construction (5%).