function calculateRentalCashFlow() {
// 1. Get Inputs
var price = parseFloat(document.getElementById('purchasePrice').value);
var closingCosts = parseFloat(document.getElementById('closingCosts').value);
var downPerc = parseFloat(document.getElementById('downPayment').value);
var interestRate = parseFloat(document.getElementById('interestRate').value);
var years = parseFloat(document.getElementById('loanTerm').value);
var rent = parseFloat(document.getElementById('monthlyRent').value);
var annualTax = parseFloat(document.getElementById('propertyTax').value);
var annualIns = parseFloat(document.getElementById('insurance').value);
var vacancyPerc = parseFloat(document.getElementById('vacancyRate').value);
var maintPerc = parseFloat(document.getElementById('maintenance').value);
var capexPerc = parseFloat(document.getElementById('capex').value);
var mgmtPerc = parseFloat(document.getElementById('managementFee').value);
// Validation
if (isNaN(price) || isNaN(rent) || isNaN(interestRate) || isNaN(years)) {
alert("Please enter valid numbers for all fields.");
return;
}
// 2. Loan Calculations
var downPaymentAmount = price * (downPerc / 100);
var loanAmount = price – downPaymentAmount;
var monthlyRate = (interestRate / 100) / 12;
var numPayments = years * 12;
// Mortgage P&I Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
var mortgagePayment = 0;
if (interestRate === 0) {
mortgagePayment = loanAmount / numPayments;
} else {
mortgagePayment = loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, numPayments)) / (Math.pow(1 + monthlyRate, numPayments) – 1);
}
// 3. Expense Calculations
var monthlyTax = annualTax / 12;
var monthlyIns = annualIns / 12;
var vacancyCost = rent * (vacancyPerc / 100);
var maintCost = rent * (maintPerc / 100);
var capexCost = rent * (capexPerc / 100);
var mgmtCost = rent * (mgmtPerc / 100);
var totalOperatingExpenses = monthlyTax + monthlyIns + vacancyCost + maintCost + capexCost + mgmtCost;
var totalMonthlyExpenses = totalOperatingExpenses + mortgagePayment;
// 4. Returns Calculations
var monthlyCashFlow = rent – totalMonthlyExpenses;
var annualCashFlow = monthlyCashFlow * 12;
var monthlyNOI = rent – totalOperatingExpenses;
var annualNOI = monthlyNOI * 12;
var totalCashInvested = downPaymentAmount + closingCosts;
// Avoid division by zero
var cashOnCash = 0;
if (totalCashInvested > 0) {
cashOnCash = (annualCashFlow / totalCashInvested) * 100;
}
var capRate = 0;
if (price > 0) {
capRate = (annualNOI / price) * 100;
}
// 5. Display Results
// Helper for currency
var fmt = new Intl.NumberFormat('en-US', { style: 'currency', currency: 'USD' });
document.getElementById('resCashFlow').innerText = fmt.format(monthlyCashFlow);
document.getElementById('resCashFlow').style.color = monthlyCashFlow >= 0 ? '#2e7d32' : '#c62828';
document.getElementById('resMortgage').innerText = fmt.format(mortgagePayment);
document.getElementById('resTotalExpenses').innerText = fmt.format(totalMonthlyExpenses);
document.getElementById('resNOI').innerText = fmt.format(monthlyNOI);
document.getElementById('resCoC').innerText = cashOnCash.toFixed(2) + '%';
document.getElementById('resCoC').style.color = cashOnCash >= 0 ? '#333' : '#c62828';
document.getElementById('resCapRate').innerText = capRate.toFixed(2) + '%';
document.getElementById('results').style.display = 'block';
}
Master Your Investment: Rental Property Cash Flow Calculator
Successful real estate investing isn't about guessing; it's about mathematics. This Rental Property Cash Flow Calculator is designed to help investors, landlords, and homebuyers analyze the financial viability of a potential rental property. By inputting accurate data regarding purchase price, financing, and operating expenses, you can determine if a property is an asset or a liability.
Why Calculating Cash Flow is Critical
Cash flow is the lifeblood of any rental investment. It is the money left over after all expenses—including the mortgage, taxes, insurance, and maintenance—have been paid. Positive cash flow means the property pays for itself and provides you with income. Negative cash flow means you are paying out of pocket to hold the asset.
Key Metrics Explained
NOI (Net Operating Income): This is your total income minus operating expenses. Crucially, NOI excludes mortgage payments. It measures the profitability of the property itself, regardless of financing.
Cash Flow: This is your NOI minus debt service (mortgage payments). This is the actual cash that lands in your bank account every month.
Cash on Cash Return (CoC): This metric compares your annual cash flow to the total amount of cash you actually invested (Down Payment + Closing Costs). It tells you how hard your specific dollars are working for you.
Cap Rate (Capitalization Rate): Calculated as NOI divided by the Purchase Price. It represents the potential return on investment if you bought the property entirely with cash. It is excellent for comparing properties across different markets.
How to Estimate Expenses
One of the biggest mistakes new investors make is underestimating expenses. Use these guidelines when filling out the calculator:
Vacancy Rate: No property is occupied 100% of the time. A standard conservative estimate is 5% to 8% (roughly 2-4 weeks per year).
Maintenance & Repairs: Budget 5-10% of rent for ongoing fixes like leaky faucets or painting.
CapEx (Capital Expenditures): This is saving for "big ticket" items like a new roof, HVAC, or water heater. Allocating 5-10% ensures you aren't bankrupt when a major system fails.
Property Management: Even if you plan to manage it yourself, calculate a fee (typically 8-10%) to see if the deal still works if you decide to hire a manager later.
Example Calculation
Imagine you buy a property for $200,000 with 20% down. Your loan is $160,000 at 6.5% interest.
Monthly Rent: $2,000
Mortgage (P&I): ~$1,011
Taxes & Insurance: ~$350
Reserves (Vacancy/Maint/CapEx/Mgmt): ~$500
If your total expenses are roughly $1,861, your Positive Cash Flow is $139 per month. Using this calculator allows you to tweak the purchase price or interest rate to see how you can improve that margin.