function calculateRental() {
// 1. Get Values
var price = parseFloat(document.getElementById('propPrice').value);
var down = parseFloat(document.getElementById('downPayment').value);
var rate = parseFloat(document.getElementById('intRate').value);
var years = parseFloat(document.getElementById('loanTerm').value);
var rent = parseFloat(document.getElementById('monthlyRent').value);
var vacancy = parseFloat(document.getElementById('vacancyRate').value);
var tax = parseFloat(document.getElementById('annualTax').value);
var ins = parseFloat(document.getElementById('annualIns').value);
var maint = parseFloat(document.getElementById('maintCost').value);
var hoa = parseFloat(document.getElementById('hoaFee').value);
// 2. Validate
if (isNaN(price) || isNaN(down) || isNaN(rent) || isNaN(years)) {
document.getElementById('calcError').style.display = 'block';
document.getElementById('calcResults').style.display = 'none';
return;
}
document.getElementById('calcError').style.display = 'none';
// 3. Logic
// Loan Calculation
var principal = price – down;
var monthlyMortgage = 0;
if (principal > 0) {
if (rate > 0) {
var monthlyRate = (rate / 100) / 12;
var numberOfPayments = years * 12;
monthlyMortgage = principal * (monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments)) / (Math.pow(1 + monthlyRate, numberOfPayments) – 1);
} else {
monthlyMortgage = principal / (years * 12);
}
}
// Monthly Expenses Calculation
var monthlyTax = tax / 12;
var monthlyIns = ins / 12;
var monthlyVacancy = rent * (vacancy / 100);
var monthlyMaint = rent * (maint / 100);
var totalMonthlyExpenses = monthlyMortgage + monthlyTax + monthlyIns + monthlyVacancy + monthlyMaint + hoa;
// Cash Flow
var monthlyCashFlow = rent – totalMonthlyExpenses;
var annualCashFlow = monthlyCashFlow * 12;
// ROI Metrics
var totalInvestment = down; // Assuming closing costs are included or negligible for this simple calc, or user puts total cash in 'down'
var cocRoi = 0;
if (totalInvestment > 0) {
cocRoi = (annualCashFlow / totalInvestment) * 100;
}
// Cap Rate = (Net Operating Income / Current Market Value)
// NOI = Annual Rent – Operating Expenses (Tax, Ins, Maint, Vacancy, HOA) – EXCLUDING Mortgage
var monthlyOpEx = monthlyTax + monthlyIns + monthlyVacancy + monthlyMaint + hoa;
var annualNOI = (rent * 12) – (monthlyOpEx * 12);
var capRate = 0;
if (price > 0) {
capRate = (annualNOI / price) * 100;
}
var opExRatio = 0;
if (rent > 0) {
opExRatio = (monthlyOpEx / rent) * 100;
}
// 4. Display Results
document.getElementById('resMortgage').innerText = "$" + monthlyMortgage.toFixed(2);
document.getElementById('resExpenses').innerText = "$" + totalMonthlyExpenses.toFixed(2);
document.getElementById('resOpExRatio').innerText = opExRatio.toFixed(2) + "%";
document.getElementById('resCashFlow').innerText = "$" + monthlyCashFlow.toFixed(2);
document.getElementById('resCashFlow').style.color = monthlyCashFlow >= 0 ? '#27ae60' : '#c0392b';
document.getElementById('resAnnualCF').innerText = "$" + annualCashFlow.toFixed(2);
document.getElementById('resCocRoi').innerText = cocRoi.toFixed(2) + "%";
document.getElementById('resCocRoi').style.color = cocRoi >= 0 ? '#27ae60' : '#c0392b';
document.getElementById('resCapRate').innerText = capRate.toFixed(2) + "%";
document.getElementById('calcResults').style.display = 'block';
}
Understanding Your Rental Property ROI
Investing in real estate is one of the most reliable ways to build wealth, but simply buying a property doesn't guarantee profit. To ensure your investment is sound, you need to analyze the numbers deeply. This Rental Property Cash Flow Calculator helps you evaluate the profitability of a potential real estate deal by factoring in income, operating expenses, and financing costs.
Key Metrics Explained
Monthly Cash Flow: This is your profit (or loss) every month after all expenses, including the mortgage, have been paid. Positive cash flow is essential for a sustainable investment.
Cash on Cash (CoC) ROI: This metric calculates the cash return on the actual cash you invested (Down Payment). It is calculated as Annual Cash Flow / Total Cash Invested. A good CoC ROI typically ranges from 8% to 12% or higher depending on the market.
Cap Rate (Capitalization Rate): This measures the rate of return on the property assuming you paid all cash (no mortgage). It helps you compare the profitability of different properties regardless of how they are financed. Formula: Net Operating Income / Purchase Price.
Operating Expense Ratio: This represents the percentage of your rental income that goes toward operating expenses (excluding the mortgage). Keeping this low maximizes your NOI.
How to Use This Calculator
Purchase Price & Loan Details: Enter the cost of the property and your financing terms. The calculator will automatically determine your monthly Principal & Interest (P&I) payments.
Income & Vacancy: Input the expected monthly rent. Be sure to account for a Vacancy Rate (typically 5-8%), which accounts for periods when the property sits empty between tenants.
Expenses: Real estate isn't just about the mortgage. You must account for Property Taxes, Insurance, Maintenance reserves (usually 5-10% of rent), and HOA fees if applicable.
By accurately inputting these figures, you can avoid "negative cash flow" properties that drain your bank account rather than filling it.