Analyze your real estate investment deal in seconds.
Purchase & Loan
Rental Income
Recurring Expenses
Investment Analysis
Monthly Cash Flow
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Cash on Cash ROI
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Cap Rate
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NOI (Monthly)
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Total Monthly Expenses
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Mortgage Payment
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Understanding Rental Property Cash Flow
Investing in real estate is one of the most reliable ways to build wealth, but the success of any rental property hinges on the numbers. This Rental Property Cash Flow Calculator helps investors determine if a potential deal will generate positive income or become a financial liability.
What is Cash Flow?
Cash flow is the net amount of cash moving in and out of an investment. In real estate, it is calculated as:
Cash Flow = Total Rental Income – Total Expenses
Total expenses include your mortgage payment (Principal & Interest), taxes, insurance, vacancy reserves, repairs, and property management fees. Positive cash flow means the property pays for itself and puts money in your pocket every month.
Key Metrics Explained
NOI (Net Operating Income): This is your annual income minus operating expenses, excluding the mortgage payment. It measures the profitability of the property itself, regardless of financing.
Cash on Cash Return (CoC): This percentage measures the annual return on the actual cash you invested (Down Payment + Closing Costs). It is a critical metric for comparing real estate against other investment vehicles like stocks.
Cap Rate (Capitalization Rate): Calculated as NOI divided by the property purchase price. It represents the potential return on an investment assuming you bought the property with all cash.
How to Estimate Expenses Accurately
New investors often overestimate cash flow by underestimating expenses. Always account for:
Vacancy: Properties won't be occupied 365 days a year. A standard safe estimate is 5-8% (about one month per year).
Maintenance: Things break. Setting aside 5-10% of the rent for repairs ensures you aren't caught off guard by a broken water heater.
Management Fees: Even if you plan to self-manage, include a 10% management fee in your calculations. This ensures the deal still makes sense if you eventually hire a property manager.
Interpreting Your Results
If your Monthly Cash Flow is positive (e.g., $200+ per door), the property is an asset. If it is negative, you are subsidizing the tenant's housing. While appreciation is a bonus, experienced investors prioritize immediate positive cash flow to ensure sustainability.
function calculateRentalProperty() {
// 1. Get Inputs
var purchasePrice = parseFloat(document.getElementById("purchasePrice").value) || 0;
var downPaymentPercent = parseFloat(document.getElementById("downPayment").value) || 0;
var interestRate = parseFloat(document.getElementById("interestRate").value) || 0;
var loanTerm = parseFloat(document.getElementById("loanTerm").value) || 0;
var closingCosts = parseFloat(document.getElementById("closingCosts").value) || 0;
var grossRent = parseFloat(document.getElementById("grossRent").value) || 0;
var otherIncome = parseFloat(document.getElementById("otherIncome").value) || 0;
var vacancyRate = parseFloat(document.getElementById("vacancyRate").value) || 0;
var propertyTaxAnnual = parseFloat(document.getElementById("propertyTax").value) || 0;
var insuranceAnnual = parseFloat(document.getElementById("insurance").value) || 0;
var hoaFees = parseFloat(document.getElementById("hoaFees").value) || 0;
var maintenancePercent = parseFloat(document.getElementById("maintenance").value) || 0;
var managementFeePercent = parseFloat(document.getElementById("managementFee").value) || 0;
// 2. Loan Calculations
var downPaymentAmount = purchasePrice * (downPaymentPercent / 100);
var loanAmount = purchasePrice – downPaymentAmount;
var monthlyRate = (interestRate / 100) / 12;
var totalPayments = loanTerm * 12;
var monthlyMortgage = 0;
if (loanAmount > 0 && interestRate > 0) {
monthlyMortgage = loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, totalPayments)) / (Math.pow(1 + monthlyRate, totalPayments) – 1);
} else if (loanAmount > 0 && interestRate === 0) {
monthlyMortgage = loanAmount / totalPayments;
}
// 3. Income Calculations
var totalMonthlyIncome = grossRent + otherIncome;
var vacancyCost = totalMonthlyIncome * (vacancyRate / 100);
var effectiveIncome = totalMonthlyIncome – vacancyCost;
// 4. Operating Expense Calculations
var monthlyTax = propertyTaxAnnual / 12;
var monthlyInsurance = insuranceAnnual / 12;
var maintenanceCost = totalMonthlyIncome * (maintenancePercent / 100);
var managementCost = totalMonthlyIncome * (managementFeePercent / 100);
var totalOperatingExpenses = monthlyTax + monthlyInsurance + hoaFees + maintenanceCost + managementCost;
// 5. Profitability Metrics
var noiMonthly = effectiveIncome – totalOperatingExpenses;
var noiAnnual = noiMonthly * 12;
var monthlyCashFlow = noiMonthly – monthlyMortgage;
var annualCashFlow = monthlyCashFlow * 12;
var totalCashInvested = downPaymentAmount + closingCosts;
var cashOnCash = 0;
if (totalCashInvested > 0) {
cashOnCash = (annualCashFlow / totalCashInvested) * 100;
}
var capRate = 0;
if (purchasePrice > 0) {
capRate = (noiAnnual / purchasePrice) * 100;
}
var totalMonthlyExpenses = totalOperatingExpenses + monthlyMortgage + vacancyCost; // Vacancy is technically lost income, but often viewed as expense outflow in simple logic, here we treat it as deduction from income for NOI, but for total "outflow" vs gross rent it matters.
// Let's standardize: Expense display usually includes PITI + Maint + CapEx + PM + HOA.
// We will display Total Expenses as (Operating Expenses + Mortgage). Vacancy was deducted from Income.
var displayTotalExp = totalOperatingExpenses + monthlyMortgage;
// 6. Display Results
var cashFlowElement = document.getElementById("displayCashFlow");
cashFlowElement.innerText = formatCurrency(monthlyCashFlow);
if (monthlyCashFlow >= 0) {
cashFlowElement.className = "result-value cash-flow-positive";
} else {
cashFlowElement.className = "result-value cash-flow-negative";
}
document.getElementById("displayCoc").innerText = cashOnCash.toFixed(2) + "%";
document.getElementById("displayCap").innerText = capRate.toFixed(2) + "%";
document.getElementById("displayNOI").innerText = formatCurrency(noiMonthly);
document.getElementById("displayExpenses").innerText = formatCurrency(displayTotalExp);
document.getElementById("displayMortgage").innerText = formatCurrency(monthlyMortgage);
document.getElementById("resultsBox").style.display = "block";
// Scroll to results
document.getElementById("resultsBox").scrollIntoView({behavior: "smooth"});
}
function formatCurrency(num) {
return "$" + num.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
}