function calculateRental() {
// 1. Get Inputs
var price = parseFloat(document.getElementById('rp_purchase_price').value) || 0;
var downPercent = parseFloat(document.getElementById('rp_down_payment').value) || 0;
var rate = parseFloat(document.getElementById('rp_interest_rate').value) || 0;
var years = parseFloat(document.getElementById('rp_loan_term').value) || 0;
var closingCosts = parseFloat(document.getElementById('rp_closing_costs').value) || 0;
var rent = parseFloat(document.getElementById('rp_monthly_rent').value) || 0;
var vacancyPercent = parseFloat(document.getElementById('rp_vacancy').value) || 0;
var annualTaxes = parseFloat(document.getElementById('rp_annual_taxes').value) || 0;
var annualInsurance = parseFloat(document.getElementById('rp_annual_insurance').value) || 0;
var hoa = parseFloat(document.getElementById('rp_monthly_hoa').value) || 0;
var repairs = parseFloat(document.getElementById('rp_monthly_repairs').value) || 0;
var mgmtPercent = parseFloat(document.getElementById('rp_mgmt_fee').value) || 0;
// 2. Calculate Mortgage
var downPayment = price * (downPercent / 100);
var loanAmount = price – downPayment;
var monthlyRate = (rate / 100) / 12;
var totalMonths = years * 12;
var mortgagePayment = 0;
if (rate > 0 && years > 0) {
mortgagePayment = loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, totalMonths)) / (Math.pow(1 + monthlyRate, totalMonths) – 1);
} else if (years > 0) {
mortgagePayment = loanAmount / totalMonths;
}
// 3. Calculate Expenses
var vacancyCost = rent * (vacancyPercent / 100);
var mgmtCost = rent * (mgmtPercent / 100);
var monthlyTaxes = annualTaxes / 12;
var monthlyInsurance = annualInsurance / 12;
// Operating Expenses (excluding mortgage)
var operatingExpenses = vacancyCost + mgmtCost + monthlyTaxes + monthlyInsurance + hoa + repairs;
// Total Expenses (including mortgage)
var totalExpenses = operatingExpenses + mortgagePayment;
// 4. Calculate Metrics
var monthlyNOI = rent – operatingExpenses; // Net Operating Income
var monthlyCashFlow = rent – totalExpenses;
var annualCashFlow = monthlyCashFlow * 12;
var annualNOI = monthlyNOI * 12;
var totalInitialInvestment = downPayment + 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 resBox = document.getElementById('rp_results_box');
resBox.style.display = "block";
document.getElementById('res_mortgage').innerText = "$" + mortgagePayment.toFixed(2);
document.getElementById('res_expenses').innerText = "$" + totalExpenses.toFixed(2);
document.getElementById('res_noi').innerText = "$" + monthlyNOI.toFixed(2);
var cfElement = document.getElementById('res_cashflow');
cfElement.innerText = "$" + monthlyCashFlow.toFixed(2);
if (monthlyCashFlow >= 0) {
cfElement.className = "rp-result-value rp-highlight";
} else {
cfElement.className = "rp-result-value rp-highlight-neg";
}
var cocElement = document.getElementById('res_coc');
cocElement.innerText = cocReturn.toFixed(2) + "%";
if (cocReturn >= 0) {
cocElement.className = "rp-result-value rp-highlight";
} else {
cocElement.className = "rp-result-value rp-highlight-neg";
}
document.getElementById('res_cap').innerText = capRate.toFixed(2) + "%";
}
Analyze Your Investment: Rental Property Cash Flow Calculator
Investing in real estate is one of the most reliable ways to build wealth, but it relies heavily on the numbers. Unlike emotional purchases like a primary residence, a rental property is a business. The primary metric for the success of that business is Cash Flow.
This Rental Property Cash Flow Calculator is designed to give investors a clear, comprehensive view of a property's financial performance. By accounting for not just the mortgage, but "hidden" costs like vacancy, maintenance, and capital expenditures (CapEx), you can determine if a deal is truly profitable before you sign the contract.
What is Positive Cash Flow?
Positive cash flow occurs when the monthly rental income exceeds all of the property's expenses. This includes the mortgage (principal and interest), taxes, insurance, and operating costs. If the calculation results in a negative number, the property is "cash flow negative," meaning you will have to pay out of pocket every month to keep the investment afloat.
Key Metrics Explained
Net Operating Income (NOI): This is the total income generated by the property minus all operating expenses. Crucially, NOI excludes mortgage payments. It helps you understand the profitability of the asset itself, regardless of how it is financed.
Cap Rate (Capitalization Rate): Calculated as NOI / Purchase Price. This percentage represents the theoretical return on investment if you bought the property entirely with cash. It is the industry standard for comparing the relative value of different properties.
Cash on Cash Return (CoC): Calculated as Annual Cash Flow / Total Cash Invested. This tells you how hard your actual dollars are working. If you put $50,000 down and make $5,000 a year in profit, your CoC is 10%.
How to Estimate Expenses Accurately
One of the biggest mistakes new investors make is underestimating expenses. When using this calculator, ensure you are realistic:
Vacancy Rate: Always assume the property will be empty for a portion of the year. A standard safe estimate is 5% to 8% (roughly 2-4 weeks per year).
Maintenance & Repairs: Even if the house is new, things break. Budgeting 1% of the property value per year, or 10% of the rent, is a prudent way to build a reserve fund for roofs, HVAC systems, and plumbing issues.
Property Management: Even if you plan to self-manage, include a management fee (typically 8-10%) in your calculation. This ensures you are "paying yourself" for the work, and the deal still makes sense if you eventually hire a pro.
Interpreting Your Results
If your Cash Flow is green, the property pays for itself and generates income. If it is red, proceed with caution. While some investors accept negative cash flow in high-appreciation markets, it significantly increases risk. A healthy Cash on Cash Return typically ranges from 8% to 12% for residential rentals, though this varies significantly by market.