Understanding the numbers behind a rental property is crucial for real estate investors. The difference between a profitable investment and a financial burden often lies in the accuracy of your cash flow analysis. This Rental Property Cash Flow Calculator helps you break down income, expenses, and debt service to see the true monthly profit.
Key Metrics Explained
Gross Operating Income: This is your total potential rental income minus estimated vacancy losses. No property is occupied 100% of the time, so factoring in a vacancy rate (usually 5-8%) is essential for realistic projections.
Net Operating Income (NOI): This is a critical metric calculated by subtracting all operating expenses (taxes, insurance, repairs, management) from your effective gross income. Note that NOI does not include mortgage payments.
Cash Flow: This is the net amount of cash moving in or out of the business after all expenses and mortgage payments (debt service) have been paid. Positive cash flow means the property pays for itself and generates income.
Cash on Cash Return: This percentage tells you how hard your money is working. It compares your annual pre-tax cash flow to the total cash invested (down payment + closing costs + rehab costs). A common benchmark for a good cash on cash return is 8-12%, though this varies by market strategy.
Estimating Expenses
Many new investors make the mistake of underestimating expenses. Beyond the mortgage, you must account for property taxes, landlord insurance, property management fees (typically 8-10% of rent), and maintenance reserves. A good rule of thumb for maintenance is to set aside 10-15% of the monthly rent to cover future repairs like roof replacements or HVAC issues.
function calculateRentalCashFlow() {
// 1. Get Input Values using var
var purchasePrice = parseFloat(document.getElementById('rc_purchasePrice').value);
var downPercent = parseFloat(document.getElementById('rc_downPaymentPercent').value);
var interestRate = parseFloat(document.getElementById('rc_interestRate').value);
var loanTermYears = parseFloat(document.getElementById('rc_loanTerm').value);
var monthlyRent = parseFloat(document.getElementById('rc_monthlyRent').value);
var vacancyRate = parseFloat(document.getElementById('rc_vacancyRate').value);
var annualTax = parseFloat(document.getElementById('rc_propertyTax').value);
var annualInsurance = parseFloat(document.getElementById('rc_insurance').value);
var monthlyRepairs = parseFloat(document.getElementById('rc_repairCosts').value);
var mgmtFeePercent = parseFloat(document.getElementById('rc_mgmtFee').value);
// Validate inputs
if (isNaN(purchasePrice) || isNaN(monthlyRent) || isNaN(interestRate)) {
alert("Please enter valid numbers for Price, Rent, and Interest Rate.");
return;
}
// 2. Perform Calculations
// Mortgage Calculation
var downPaymentAmount = purchasePrice * (downPercent / 100);
var loanAmount = purchasePrice – downPaymentAmount;
var monthlyRate = (interestRate / 100) / 12;
var totalPayments = loanTermYears * 12;
var monthlyMortgage = 0;
if (interestRate > 0) {
monthlyMortgage = loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, totalPayments)) / (Math.pow(1 + monthlyRate, totalPayments) – 1);
} else {
monthlyMortgage = loanAmount / totalPayments;
}
// Income calculations
var vacancyLoss = monthlyRent * (vacancyRate / 100);
var effectiveGrossIncome = monthlyRent – vacancyLoss;
// Expense calculations (Monthly)
var monthlyTax = annualTax / 12;
var monthlyInsurance = annualInsurance / 12;
var mgmtCost = monthlyRent * (mgmtFeePercent / 100);
var totalMonthlyOperatingExpenses = monthlyTax + monthlyInsurance + monthlyRepairs + mgmtCost;
var totalMonthlyExpenses = totalMonthlyOperatingExpenses + monthlyMortgage + vacancyLoss;
// Note: Vacancy is often treated as contra-income, but for "total outflow" visualization we can sum relevant parts.
// Standard Cash Flow = (Rent – Vacancy) – (Operating Expenses + Mortgage).
var monthlyCashFlow = effectiveGrossIncome – totalMonthlyOperatingExpenses – monthlyMortgage;
var annualCashFlow = monthlyCashFlow * 12;
// NOI (Annual) = (Annual Effective Income) – (Annual Operating Expenses)
// Mortgage is NOT included in NOI
var annualEffectiveIncome = effectiveGrossIncome * 12;
var annualOperatingExpenses = totalMonthlyOperatingExpenses * 12;
var annualNOI = annualEffectiveIncome – annualOperatingExpenses;
// Cash on Cash Return
// For simplicity, we assume Total Cash Invested = Down Payment.
// (Ideally includes closing costs/rehab, but keeping inputs manageable)
var cashOnCash = 0;
if (downPaymentAmount > 0) {
cashOnCash = (annualCashFlow / downPaymentAmount) * 100;
}
// 3. Format and Display Results
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2
});
document.getElementById('val_grossRent').innerText = formatter.format(monthlyRent);
document.getElementById('val_vacancy').innerText = "-" + formatter.format(vacancyLoss);
document.getElementById('val_mgmt').innerText = "-" + formatter.format(mgmtCost);
document.getElementById('val_mortgage').innerText = "-" + formatter.format(monthlyMortgage);
// Sum of all money leaving (Vacancy loss is opportunity cost, but for cash out of pocket context:
// Usually displayed: Income – Vacancy = EGI. EGI – Expenses – Debt = CF.
// Let's display "Total Monthly Costs" as Ops + Debt.
var costsToDisplay = totalMonthlyOperatingExpenses + monthlyMortgage;
document.getElementById('val_expenses').innerText = "-" + formatter.format(costsToDisplay);
var cfElement = document.getElementById('val_cashFlow');
cfElement.innerText = formatter.format(monthlyCashFlow);
// Styling based on positive/negative
if(monthlyCashFlow >= 0) {
cfElement.className = "rental-result-value positive-cf";
} else {
cfElement.className = "rental-result-value negative-cf";
}
document.getElementById('val_totalInvested').innerText = formatter.format(downPaymentAmount);
document.getElementById('val_noi').innerText = formatter.format(annualNOI);
document.getElementById('val_coc').innerText = cashOnCash.toFixed(2) + "%";
// Show results container
document.getElementById('rc_results').style.display = "block";
}