function calculateRentalROI() {
// 1. Get Input Values
var price = parseFloat(document.getElementById('rpc-price').value) || 0;
var downPercent = parseFloat(document.getElementById('rpc-down').value) || 0;
var rate = parseFloat(document.getElementById('rpc-rate').value) || 0;
var term = parseFloat(document.getElementById('rpc-term').value) || 0;
var rent = parseFloat(document.getElementById('rpc-rent').value) || 0;
var vacancyRate = parseFloat(document.getElementById('rpc-vacancy').value) || 0;
var taxYear = parseFloat(document.getElementById('rpc-tax').value) || 0;
var insYear = parseFloat(document.getElementById('rpc-insurance').value) || 0;
var maintRate = parseFloat(document.getElementById('rpc-maintenance').value) || 0;
var mgmtRate = parseFloat(document.getElementById('rpc-management').value) || 0;
// 2. Validate essential inputs
if (price 0 && term > 0) {
monthlyMortgage = loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, numPayments)) / (Math.pow(1 + monthlyRate, numPayments) – 1);
} else {
monthlyMortgage = 0; // Cash purchase or invalid term
}
// 4. Logic: Income & Expenses
var vacancyCost = rent * (vacancyRate / 100);
var effectiveGrossIncome = rent – vacancyCost;
var monthlyTax = taxYear / 12;
var monthlyIns = insYear / 12;
var maintCost = rent * (maintRate / 100);
var mgmtCost = rent * (mgmtRate / 100);
var totalOperatingExpenses = monthlyTax + monthlyIns + maintCost + mgmtCost;
var noi = effectiveGrossIncome – totalOperatingExpenses; // Net Operating Income (Monthly)
var cashFlow = noi – monthlyMortgage;
// 5. Logic: ROI Metrics
var annualNOI = noi * 12;
var annualCashFlow = cashFlow * 12;
var totalInvestment = downPayment; // Keeping it simple (add closing costs here if field existed)
// Prevent division by zero
if (totalInvestment === 0) totalInvestment = price; // Edge case for 0 down
var cocRoi = (annualCashFlow / totalInvestment) * 100;
var capRate = (annualNOI / price) * 100;
// 6. Update UI
var cashFlowEl = document.getElementById('rpc-res-cashflow');
cashFlowEl.innerHTML = formatMoney(cashFlow);
// Color coding cash flow
if (cashFlow >= 0) {
cashFlowEl.className = "rpc-result-value rpc-highlight";
} else {
cashFlowEl.className = "rpc-result-value rpc-highlight-neg";
}
document.getElementById('rpc-res-coc').innerHTML = cocRoi.toFixed(2) + "%";
document.getElementById('rpc-res-cap').innerHTML = capRate.toFixed(2) + "%";
document.getElementById('rpc-res-noi').innerHTML = formatMoney(noi);
document.getElementById('rpc-res-expenses').innerHTML = formatMoney(totalOperatingExpenses);
document.getElementById('rpc-res-mortgage').innerHTML = formatMoney(monthlyMortgage);
// Show results
document.getElementById('rpc-results-box').style.display = "block";
}
function formatMoney(number) {
return "$" + number.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
}
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 a profit. To be a successful investor, you must analyze the numbers objectively. This Rental Property Cash Flow Calculator helps you determine the viability of a potential investment by breaking down income, operating expenses, and debt service.
How to Calculate Cash Flow
Cash flow is the net amount of money moving into or out of a business or investment. For a rental property, the formula is:
- Gross Income: Total rent collected.
- Minus Vacancy: Rent lost due to empty units (usually estimated at 5-10%).
- Minus Operating Expenses: Property taxes, insurance, management fees, and maintenance.
- Minus Debt Service: Your monthly mortgage principal and interest payments.
- Equals Cash Flow: The money that lands in your pocket every month.
Key Metrics Defined
Net Operating Income (NOI): This is arguably the most important metric in real estate. It represents the profitability of the property before debt is considered. It is calculated by subtracting operating expenses from effective gross income. Lenders look at NOI to determine if a property generates enough income to cover the loan.
Cap Rate (Capitalization Rate): The Cap Rate measures the natural rate of return on the property if it were bought in cash. It is calculated as Annual NOI / Purchase Price. A higher Cap Rate generally indicates a better return, though it may also come with higher risk (e.g., properties in declining neighborhoods often have high Cap Rates).
Cash on Cash Return (CoC ROI): While Cap Rate judges the property, CoC ROI judges your specific investment performance based on the financing you used. It answers the question: "For every dollar I put into this deal (down payment), how much am I getting back annually?" Ideally, you want a CoC return that beats the stock market or other passive investment vehicles.
Example Scenario
Imagine you purchase a property for $250,000 with 20% down ($50,000). Your loan is $200,000 at 6.5% interest.
- Rental Income: $2,200/month.
- Expenses (Tax, Ins, Maint, Vacancy): $900/month.
- Mortgage Payment: ~$1,264/month.
- Cash Flow: $2,200 – $900 – $1,264 = $36/month.
In this scenario, the cash flow is positive but thin. A slight increase in repairs could turn it negative. Use the calculator above to adjust the Purchase Price or Rent to see what is required to achieve your target monthly cash flow (e.g., $200/month per door).