function calculateRentalKPIs() {
// 1. Get Values
var price = parseFloat(document.getElementById("rpc_price").value) || 0;
var down = 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 taxAnnual = parseFloat(document.getElementById("rpc_tax").value) || 0;
var insAnnual = parseFloat(document.getElementById("rpc_ins").value) || 0;
var hoaMonthly = parseFloat(document.getElementById("rpc_hoa").value) || 0;
var vacancyRate = parseFloat(document.getElementById("rpc_vacancy").value) || 0;
var maintRate = parseFloat(document.getElementById("rpc_maint").value) || 0;
// 2. Mortgage Calculation
var loanAmount = price – down;
var monthlyRate = (rate / 100) / 12;
var numberOfPayments = term * 12;
var monthlyMortgage = 0;
if (loanAmount > 0 && rate > 0) {
monthlyMortgage = loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments)) / (Math.pow(1 + monthlyRate, numberOfPayments) – 1);
} else if (loanAmount > 0 && rate === 0) {
monthlyMortgage = loanAmount / numberOfPayments;
}
// 3. Operating Expenses Calculation
var vacancyCost = rent * (vacancyRate / 100);
var maintCost = rent * (maintRate / 100);
var taxMonthly = taxAnnual / 12;
var insMonthly = insAnnual / 12;
var totalOperatingExpensesMonthly = taxMonthly + insMonthly + hoaMonthly + vacancyCost + maintCost;
var totalExpensesWithMortgage = totalOperatingExpensesMonthly + monthlyMortgage;
// 4. KPI Calculations
var monthlyCashFlow = rent – totalExpensesWithMortgage;
var annualCashFlow = monthlyCashFlow * 12;
// Net Operating Income (NOI) = (Gross Income – Operating Expenses) * 12. NOI Excludes mortgage.
var monthlyNOI = rent – totalOperatingExpensesMonthly;
var annualNOI = monthlyNOI * 12;
// Cap Rate = (Annual NOI / Purchase Price) * 100
var capRate = (price > 0) ? (annualNOI / price) * 100 : 0;
// Cash on Cash Return = (Annual Cash Flow / Total Cash Invested) * 100
// Simplified: Cash Invested = Down Payment. (Closing costs ignored for simplicity in this version)
var cashInvested = down;
var cocReturn = (cashInvested > 0) ? (annualCashFlow / cashInvested) * 100 : 0;
// 5. Update DOM
document.getElementById("res_mortgage").innerHTML = "$" + monthlyMortgage.toFixed(2);
document.getElementById("res_expenses").innerHTML = "$" + totalExpensesWithMortgage.toFixed(2);
document.getElementById("res_noi").innerHTML = "$" + annualNOI.toFixed(2);
var cashFlowEl = document.getElementById("res_cashflow");
cashFlowEl.innerHTML = "$" + monthlyCashFlow.toFixed(2);
if(monthlyCashFlow >= 0) {
cashFlowEl.className = "rpc-result-value rpc-highlight";
} else {
cashFlowEl.className = "rpc-result-value rpc-highlight-neg";
}
var cocEl = document.getElementById("res_coc");
cocEl.innerHTML = cocReturn.toFixed(2) + "%";
if(cocReturn >= 0) cocEl.style.color = "#27ae60"; else cocEl.style.color = "#c0392b";
document.getElementById("res_cap").innerHTML = capRate.toFixed(2) + "%";
// Show results
document.getElementById("rpc_results").style.display = "block";
}
Understanding Your Rental Property Numbers
Investing in real estate is a numbers game. Before signing a contract, it is crucial to understand if a property will be an asset (putting money in your pocket) or a liability (taking money out). This Rental Property Cash Flow Calculator helps you analyze a potential deal by breaking down the income, expenses, and returns.
What is Monthly Cash Flow?
Monthly Cash Flow is the net amount of money left over after all expenses are paid. It is calculated by taking your total monthly rental income and subtracting your mortgage payment, property taxes, insurance, HOA fees, and allowances for vacancy and maintenance. A positive cash flow means the property pays for itself and generates profit.
Cap Rate vs. Cash-on-Cash Return
Two of the most important metrics for real estate investors are the Cap Rate and the Cash-on-Cash Return:
Cap Rate (Capitalization Rate): This measures the natural rate of return on the property assuming you bought it with all cash. It is calculated as (Net Operating Income / Purchase Price). It helps compare the profitability of different properties regardless of how they are financed.
Cash-on-Cash Return: This measures the return on the actual cash you invested (down payment). It is calculated as (Annual Cash Flow / Total Cash Invested). This is often the more practical metric for investors using leverage (loans).
Why Include Vacancy and Maintenance?
Many new investors make the mistake of calculating returns based only on rent minus mortgage. However, real life happens. Tenants move out (Vacancy) and toilets break (Maintenance). A conservative analysis usually sets aside 5% to 10% of the monthly rent for each of these categories to ensure you aren't caught off guard by unexpected costs.
What is a Good ROI for Rental Property?
While "good" is subjective, many investors look for a Cash-on-Cash return of 8% to 12% or higher. In high-appreciation markets, investors might accept a lower cash flow (or even break-even) in exchange for long-term equity growth, whereas in stable markets, immediate cash flow is the priority.