function calculateRental() {
// 1. Get Inputs
var price = parseFloat(document.getElementById('purchasePrice').value) || 0;
var downPct = parseFloat(document.getElementById('downPayment').value) || 0;
var interestRate = parseFloat(document.getElementById('interestRate').value) || 0;
var termYears = parseFloat(document.getElementById('loanTerm').value) || 0;
var closingCosts = parseFloat(document.getElementById('closingCosts').value) || 0;
var rent = parseFloat(document.getElementById('monthlyRent').value) || 0;
var annualTax = parseFloat(document.getElementById('propertyTax').value) || 0;
var annualIns = parseFloat(document.getElementById('homeInsurance').value) || 0;
var monthlyHOA = parseFloat(document.getElementById('hoaFee').value) || 0;
var vacancyPct = parseFloat(document.getElementById('vacancyRate').value) || 0;
var maintPct = parseFloat(document.getElementById('maintenanceRate').value) || 0;
var mgmtPct = parseFloat(document.getElementById('managementFee').value) || 0;
// 2. Calculate Mortgage (Principal & Interest)
var downAmount = price * (downPct / 100);
var loanAmount = price – downAmount;
var monthlyRate = (interestRate / 100) / 12;
var numPayments = termYears * 12;
var mortgagePayment = 0;
if (monthlyRate > 0 && numPayments > 0) {
mortgagePayment = loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, numPayments)) / (Math.pow(1 + monthlyRate, numPayments) – 1);
} else if (numPayments > 0) {
mortgagePayment = loanAmount / numPayments;
}
// 3. Calculate Monthly Operating Expenses
var monthlyTax = annualTax / 12;
var monthlyIns = annualIns / 12;
var monthlyVacancy = rent * (vacancyPct / 100);
var monthlyMaint = rent * (maintPct / 100);
var monthlyMgmt = rent * (mgmtPct / 100);
var operatingExpenses = monthlyTax + monthlyIns + monthlyHOA + monthlyVacancy + monthlyMaint + monthlyMgmt;
var totalExpenses = operatingExpenses + mortgagePayment;
// 4. Calculate Key Metrics
var cashFlow = rent – totalExpenses;
var annualCashFlow = cashFlow * 12;
var annualNOI = (rent – operatingExpenses) * 12;
var totalInitialInvestment = downAmount + closingCosts;
var cocReturn = 0;
if (totalInitialInvestment > 0) {
cocReturn = (annualCashFlow / totalInitialInvestment) * 100;
}
var capRate = 0;
if (price > 0) {
capRate = (annualNOI / price) * 100;
}
// 5. Update UI
var resultBox = document.getElementById('resultContainer');
resultBox.style.display = 'block';
// Helper for formatting currency
function fmtMoney(num) {
return '$' + num.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
}
function fmtPct(num) {
return num.toFixed(2) + '%';
}
var cfDisplay = document.getElementById('monthlyCashFlowDisplay');
cfDisplay.innerHTML = fmtMoney(cashFlow);
// Color coding for cash flow
if (cashFlow >= 0) {
cfDisplay.className = "result-value highlight-positive";
} else {
cfDisplay.className = "result-value highlight-negative";
}
document.getElementById('noiDisplay').innerHTML = fmtMoney(annualNOI / 12);
document.getElementById('totalExpensesDisplay').innerHTML = fmtMoney(totalExpenses);
document.getElementById('mortgageDisplay').innerHTML = fmtMoney(mortgagePayment);
document.getElementById('cocDisplay').innerHTML = fmtPct(cocReturn);
document.getElementById('capRateDisplay').innerHTML = fmtPct(capRate);
}
Understanding Rental Property Cash Flow
Investing in real estate is one of the most reliable ways to build wealth, but not every property is a good deal. The most critical metric for buy-and-hold investors is Cash Flow. This calculator helps you analyze a potential rental property deal by breaking down income, operating expenses, and financing costs to determine if an asset will put money in your pocket every month.
What is Monthly Cash Flow?
Monthly cash flow is the net amount of profit you generate from a rental property after all expenses are paid. The formula is simple:
Cash Flow = Total Monthly Income – Total Monthly Expenses
Income includes rent, laundry fees, or parking fees. Expenses include the mortgage, taxes, insurance, HOA fees, vacancy reserves, repairs, and property management.
Key Metrics Explained
This calculator provides three essential metrics for evaluating investment performance:
1. Net Operating Income (NOI)
NOI is the annual income generated by the property minus all operating expenses. Crucially, NOI excludes mortgage payments. It measures the profitability of the property itself, regardless of how it is financed.
2. Cash on Cash Return (CoC)
CoC Return measures the annual return on the actual cash you invested (down payment + closing costs). It is calculated as:
(Annual Cash Flow / Total Cash Invested) × 100
A good CoC return varies by market, but many investors aim for 8-12%.
3. Cap Rate (Capitalization Rate)
The Cap Rate indicates the rate of return on a real estate investment property based on the income that the property is expected to generate. It is useful for comparing similar properties in the same market. A higher cap rate generally implies higher risk and higher potential return.
How to Use This Calculator
To get the most accurate results, ensure you input realistic numbers:
Vacancy Rate: No property is occupied 100% of the time. Use 5-8% as a standard buffer.
Maintenance: Even new homes need repairs. Budgeting 5-10% of the rent for future repairs (CapEx) is a prudent move.
Property Management: Even if you self-manage, include this cost (usually 8-10%) to see if the deal still works if you decide to hire a manager later.