Investing in real estate is one of the most reliable ways to build long-term wealth, but not every property is a good deal. The difference between a profitable asset and a financial burden often comes down to the numbers. This Rental Property Cash Flow Calculator is designed to help investors quickly evaluate the potential profitability of a residential rental property.
What is Monthly Cash Flow?
Monthly cash flow is the net amount of money left in your pocket after all expenses are paid. It is calculated by taking your total monthly income (rent) and subtracting all operating expenses and debt service (mortgage payments). A positive cash flow means the property pays for itself and generates income, while negative cash flow means you are paying out of pocket to hold the asset.
The Formula: Cash Flow = Gross Income – (Operating Expenses + Mortgage Payment)
Understanding the Inputs
Vacancy Rate: No property is occupied 100% of the time. It is prudent to budget for a vacancy rate of 5-8% to account for turnover periods between tenants.
Maintenance: Even new homes require upkeep. Setting aside 5-10% of the rent for repairs ensures you aren't caught off guard when a water heater breaks.
Cash on Cash Return (CoC): This metric measures the annual return on the actual cash you invested (down payment + closing costs), rather than the total loan amount. It allows you to compare real estate returns against other investment vehicles like stocks.
Interpreting Your Results
When analyzing a deal, what constitutes a "good" return depends on your goals and local market. However, many investors look for:
Positive Cash Flow: At least $100-$200 per door per month for single-family homes.
Cash on Cash Return: 8-12% is generally considered solid, though in high-appreciation markets, investors may accept lower initial yields.
Use this tool to run scenarios. What happens if the interest rate rises by 1%? What if you raise the rent by $100? Adjust the numbers above to see how sensitive your investment is to market changes.
function calculateCashFlow() {
// 1. Get Input Values
var price = parseFloat(document.getElementById('purchasePrice').value);
var downPct = parseFloat(document.getElementById('downPaymentPercent').value);
var rate = parseFloat(document.getElementById('interestRate').value);
var years = parseFloat(document.getElementById('loanTerm').value);
var rent = parseFloat(document.getElementById('monthlyRent').value);
var vacRate = parseFloat(document.getElementById('vacancyRate').value);
var tax = parseFloat(document.getElementById('annualTaxes').value);
var ins = parseFloat(document.getElementById('annualInsurance').value);
var maint = parseFloat(document.getElementById('monthlyMaintenance').value);
var hoa = parseFloat(document.getElementById('monthlyHOA').value);
// 2. Validate Inputs
if (isNaN(price) || isNaN(downPct) || isNaN(rate) || isNaN(years) || isNaN(rent)) {
alert("Please fill in all required fields (Price, Down Payment, Rate, Term, Rent) with valid numbers.");
return;
}
// Handle optional fields as 0 if empty
if (isNaN(vacRate)) vacRate = 0;
if (isNaN(tax)) tax = 0;
if (isNaN(ins)) ins = 0;
if (isNaN(maint)) maint = 0;
if (isNaN(hoa)) hoa = 0;
// 3. Perform Calculations
// Loan Calculation
var downPaymentAmount = price * (downPct / 100);
var loanAmount = price – downPaymentAmount;
// Mortgage Payment (Monthly P&I)
// M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
var monthlyRate = (rate / 100) / 12;
var numPayments = years * 12;
var monthlyMortgage = 0;
if (rate === 0) {
monthlyMortgage = loanAmount / numPayments;
} else {
monthlyMortgage = (loanAmount * monthlyRate) / (1 – Math.pow(1 + monthlyRate, -numPayments));
}
// Monthly Expenses Breakdown
var monthlyTax = tax / 12;
var monthlyIns = ins / 12;
var monthlyVacancyCost = rent * (vacRate / 100);
// Total Monthly Expenses (Operating + Debt Service)
var operatingExpenses = monthlyTax + monthlyIns + maint + hoa + monthlyVacancyCost;
var totalMonthlyOutflow = operatingExpenses + monthlyMortgage;
// Cash Flow
var monthlyCashFlow = rent – totalMonthlyOutflow;
var annualCashFlow = monthlyCashFlow * 12;
// Net Operating Income (Income – Operating Expenses, excluding mortgage)
var noi = rent – operatingExpenses;
// Cash on Cash Return
// CoC = Annual Cash Flow / Total Cash Invested
// Assuming Cash Invested is just Down Payment for this simple calc (could add closing costs)
var cocReturn = 0;
if (downPaymentAmount > 0) {
cocReturn = (annualCashFlow / downPaymentAmount) * 100;
}
// 4. Update UI
// Formatter
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
});
document.getElementById('displayMortgage').innerHTML = formatter.format(monthlyMortgage);
document.getElementById('displayExpenses').innerHTML = formatter.format(totalMonthlyOutflow);
document.getElementById('displayNOI').innerHTML = formatter.format(noi);
document.getElementById('displayCashFlow').innerHTML = formatter.format(monthlyCashFlow);
document.getElementById('displayCoC').innerHTML = cocReturn.toFixed(2) + "%";
// Visual Styling for Cash Flow
var cfBox = document.getElementById('cashFlowBox');
if (monthlyCashFlow >= 0) {
cfBox.className = "highlight-result"; // Green style
} else {
cfBox.className = "highlight-result highlight-negative"; // Red style
}
// Show results
document.getElementById('resultsArea').style.display = "block";
}