function calculateRentalCashFlow() {
// 1. Get Inputs
var price = parseFloat(document.getElementById('rcf_price').value);
var rent = parseFloat(document.getElementById('rcf_rent').value);
var downPercent = parseFloat(document.getElementById('rcf_down').value);
var rate = parseFloat(document.getElementById('rcf_rate').value);
var term = parseFloat(document.getElementById('rcf_term').value);
var annualTax = parseFloat(document.getElementById('rcf_tax').value);
var annualIns = parseFloat(document.getElementById('rcf_ins').value);
var monthlyHoa = parseFloat(document.getElementById('rcf_hoa').value);
var repairPercent = parseFloat(document.getElementById('rcf_repair').value);
// 2. Validation
if (isNaN(price) || isNaN(rent) || isNaN(downPercent) || isNaN(rate) || isNaN(term)) {
alert("Please fill in all required fields with valid numbers.");
return;
}
// 3. Calculation Logic
var downPayment = price * (downPercent / 100);
var loanAmount = price – downPayment;
var monthlyRate = rate / 100 / 12;
var numPayments = term * 12;
// Mortgage Calculation (Principal + Interest)
var monthlyMortgage = 0;
if (rate === 0) {
monthlyMortgage = loanAmount / numPayments;
} else {
monthlyMortgage = loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, numPayments)) / (Math.pow(1 + monthlyRate, numPayments) – 1);
}
// Operating Expenses
var monthlyTax = annualTax / 12;
var monthlyIns = annualIns / 12;
var monthlyRepairs = rent * (repairPercent / 100);
var totalMonthlyOperatingExpenses = monthlyTax + monthlyIns + monthlyHoa + monthlyRepairs;
// NOI (Net Operating Income)
var monthlyNOI = rent – totalMonthlyOperatingExpenses;
var annualNOI = monthlyNOI * 12;
// Cash Flow
var monthlyCashFlow = monthlyNOI – monthlyMortgage;
var annualCashFlow = monthlyCashFlow * 12;
// Cash on Cash Return (CoC)
// Assuming 2% closing costs for a more realistic estimate
var closingCosts = price * 0.02;
var totalCashInvested = downPayment + closingCosts;
var cocReturn = (annualCashFlow / totalCashInvested) * 100;
// Cap Rate
var capRate = (annualNOI / price) * 100;
// 4. Update UI
document.getElementById('res_cashflow').innerHTML = "$" + monthlyCashFlow.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('res_coc').innerHTML = cocReturn.toFixed(2) + "%";
document.getElementById('res_cap').innerHTML = capRate.toFixed(2) + "%";
document.getElementById('res_mortgage').innerHTML = "$" + monthlyMortgage.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('res_expenses').innerHTML = "$" + totalMonthlyOperatingExpenses.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('res_noi').innerHTML = "$" + annualNOI.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
// Show results box
document.getElementById('rcf_results_box').style.display = 'block';
// Change color based on positive/negative cash flow
var flowElement = document.getElementById('res_cashflow');
if(monthlyCashFlow >= 0) {
flowElement.style.color = "#059669";
} else {
flowElement.style.color = "#dc2626";
}
}
Why Use a 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 math working in your favor. A Rental Property Cash Flow Calculator helps investors analyze a potential deal to determine if it will generate profit (positive cash flow) or cost money to hold (negative cash flow).
By inputting the purchase price, rental income, mortgage details, and operating expenses, this tool provides a clear snapshot of the property's financial health before you sign any paperwork.
Understanding the Key Metrics
1. Monthly Cash Flow
This is the "profit" left in your pocket after all expenses and mortgage payments are made.
Formula: Rental Income – (Operating Expenses + Mortgage Payment)
Goal: Most investors aim for at least $200–$300 per door in positive monthly cash flow to buffer against vacancies and major repairs.
2. Cash on Cash Return (CoC)
Cash on Cash Return measures the efficiency of your invested capital. It compares your annual pre-tax cash flow to the total cash you actually invested (Down Payment + Closing Costs).
Why it matters: Unlike ROI, which looks at total profit (including equity paydown and appreciation), CoC tells you how hard your actual cash is working for you right now. A CoC of 8-12% is generally considered a solid return in real estate.
3. Cap Rate (Capitalization Rate)
The Cap Rate measures the potential return of a property assuming you paid 100% cash (no mortgage). It is calculated by dividing the Net Operating Income (NOI) by the Purchase Price.
Usage: Cap Rate is excellent for comparing different properties side-by-side without the influence of loan terms. A higher Cap Rate typically indicates a higher return but may come with higher risk.
Operating Expenses You Must Watch
Many novice investors fail because they underestimate expenses. This calculator includes fields for the most critical costs:
Vacancy & Repairs: You won't have a tenant 100% of the time, and things will break. Setting aside 10-15% of monthly rent is a prudent safety net.
Property Taxes & Insurance: These are fixed costs that increase over time. Always verify current tax rates with the local county assessor.
HOA Fees: If investing in a condo or managed community, Homeowner Association fees can significantly eat into your cash flow.
The 1% Rule
A quick "rule of thumb" used by investors is the 1% Rule. It states that the monthly rent should be at least 1% of the total purchase price. For example, a $200,000 home should rent for $2,000/month. While not always achievable in high-cost markets, it serves as a quick initial filter to spot potential cash-flowing properties.