function calculateRentalResults() {
// 1. Get Input Values
var price = parseFloat(document.getElementById('rp_price').value) || 0;
var closingCosts = parseFloat(document.getElementById('rp_closing').value) || 0;
var downPercent = parseFloat(document.getElementById('rp_down').value) || 0;
var rate = parseFloat(document.getElementById('rp_rate').value) || 0;
var years = parseFloat(document.getElementById('rp_term').value) || 0;
var rent = parseFloat(document.getElementById('rp_rent').value) || 0;
var annualTax = parseFloat(document.getElementById('rp_tax').value) || 0;
var annualIns = parseFloat(document.getElementById('rp_insurance').value) || 0;
var monthlyHOA = parseFloat(document.getElementById('rp_hoa').value) || 0;
var vacancyRate = parseFloat(document.getElementById('rp_vacancy').value) || 0;
var repairRate = parseFloat(document.getElementById('rp_repair').value) || 0;
var capexRate = parseFloat(document.getElementById('rp_capex').value) || 0;
var mgmtRate = parseFloat(document.getElementById('rp_mgmt').value) || 0;
// 2. Calculate Mortgage
var downPayment = price * (downPercent / 100);
var loanAmount = price – downPayment;
var monthlyRate = (rate / 100) / 12;
var totalMonths = years * 12;
var monthlyPI = 0;
if (rate === 0) {
monthlyPI = loanAmount / totalMonths;
} else {
monthlyPI = (loanAmount * monthlyRate) / (1 – Math.pow(1 + monthlyRate, -totalMonths));
}
if (isNaN(monthlyPI) || !isFinite(monthlyPI)) monthlyPI = 0;
// 3. Calculate Monthly Expenses
var vacancyCost = rent * (vacancyRate / 100);
var repairCost = rent * (repairRate / 100);
var capexCost = rent * (capexRate / 100);
var mgmtCost = rent * (mgmtRate / 100);
var monthlyTax = annualTax / 12;
var monthlyIns = annualIns / 12;
var operatingExpenses = vacancyCost + repairCost + capexCost + mgmtCost + monthlyTax + monthlyIns + monthlyHOA;
var totalMonthlyExpenses = operatingExpenses + monthlyPI;
// 4. Calculate Metrics
var monthlyNOI = rent – operatingExpenses;
var monthlyCashFlow = monthlyNOI – monthlyPI;
var annualCashFlow = monthlyCashFlow * 12;
var annualNOI = monthlyNOI * 12;
var totalCashInvested = downPayment + closingCosts;
// Return on Investment
var cocReturn = 0;
if (totalCashInvested > 0) {
cocReturn = (annualCashFlow / totalCashInvested) * 100;
}
// Cap Rate
var capRate = 0;
if (price > 0) {
capRate = (annualNOI / price) * 100;
}
// 5. Update UI
var cashFlowEl = document.getElementById('res_cashflow');
cashFlowEl.innerHTML = formatCurrency(monthlyCashFlow);
if(monthlyCashFlow >= 0) {
cashFlowEl.className = "rp-result-value rp-positive";
} else {
cashFlowEl.className = "rp-result-value rp-negative";
}
document.getElementById('res_coc').innerHTML = cocReturn.toFixed(2) + '%';
document.getElementById('res_cap').innerHTML = capRate.toFixed(2) + '%';
document.getElementById('res_expenses').innerHTML = formatCurrency(totalMonthlyExpenses);
document.getElementById('res_noi').innerHTML = formatCurrency(monthlyNOI);
document.getElementById('res_invested').innerHTML = formatCurrency(totalCashInvested);
document.getElementById('rp_results').style.display = 'block';
}
function formatCurrency(num) {
return '$' + num.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
}
Understanding Your Rental Property Cash Flow Analysis
Investing in real estate is a numbers game. Whether you are analyzing a single-family home or a multi-unit apartment complex, the difference between a profitable asset and a financial liability often comes down to accurate math. This Rental Property Cash Flow Calculator is designed to give you a comprehensive view of a potential investment's performance.
Key Metrics Explained
1. Monthly Net Cash Flow
This is the "bottom line" number. It represents the money remaining in your pocket after all expenses—including the mortgage, taxes, insurance, and maintenance reserves—are paid. A positive cash flow indicates the property pays for itself and generates income, while a negative cash flow means you will need to feed the property money every month to keep it afloat.
2. Cash on Cash Return (CoC ROI)
While cash flow tells you the dollar amount you earn, the Cash on Cash Return tells you how hard your money is working. It is calculated by dividing your annual pre-tax cash flow by the total cash actually invested (Down Payment + Closing Costs). A CoC return of 8-12% is often considered a strong target for buy-and-hold investors, as it typically outperforms standard stock market indices while providing tax benefits.
3. Cap Rate (Capitalization Rate)
The Cap Rate measures the natural rate of return of the property assuming you paid all cash (no mortgage). It is calculated by dividing the Annual Net Operating Income (NOI) by the Purchase Price. This metric helps you compare the profitability of different properties regardless of how they are financed.
Why You Must Estimate Expenses Conservatively
New investors often make the mistake of only subtracting the mortgage payment from the rent to determine profit. This calculator includes inputs for "hidden" costs that erode returns over time:
Vacancy Rate: Properties do not stay rented 100% of the time. Allocating 5-8% ensures you have funds for turnover periods.
Repairs & CapEx: Toilets break and roofs need replacing. Setting aside 5-10% of rent for repairs and Capital Expenditures (CapEx) prevents a large bill from wiping out your annual profit.
Property Management: Even if you self-manage now, accounting for a typical 8-10% management fee ensures the deal still works if you decide to hire a professional later.
Use this tool to analyze multiple scenarios. Adjust the purchase price, down payment, or rental estimates to see how sensitive your returns are to changes in the market.