function calculateCashFlow() {
// 1. Get Input Values
var price = parseFloat(document.getElementById('rp-price').value);
var downPayment = parseFloat(document.getElementById('rp-down').value);
var rate = parseFloat(document.getElementById('rp-rate').value);
var term = parseFloat(document.getElementById('rp-term').value);
var monthlyRent = parseFloat(document.getElementById('rp-rent').value);
var annualTax = parseFloat(document.getElementById('rp-tax').value);
var annualInsurance = parseFloat(document.getElementById('rp-insurance').value);
var monthlyMaint = parseFloat(document.getElementById('rp-maintenance').value);
var monthlyPM = parseFloat(document.getElementById('rp-pm').value);
// 2. Validate Inputs
if (isNaN(price) || isNaN(downPayment) || isNaN(rate) || isNaN(term) || isNaN(monthlyRent)) {
alert("Please enter valid numbers for all primary fields.");
return;
}
// Default 0 for optional fields if empty/NaN
if (isNaN(annualTax)) annualTax = 0;
if (isNaN(annualInsurance)) annualInsurance = 0;
if (isNaN(monthlyMaint)) monthlyMaint = 0;
if (isNaN(monthlyPM)) monthlyPM = 0;
// 3. Calculate Mortgage (P&I)
var loanAmount = price – downPayment;
var monthlyRate = rate / 100 / 12;
var numberOfPayments = term * 12;
var monthlyMortgage = 0;
if (loanAmount > 0) {
if (rate === 0) {
monthlyMortgage = loanAmount / numberOfPayments;
} else {
monthlyMortgage = loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments)) / (Math.pow(1 + monthlyRate, numberOfPayments) – 1);
}
}
// 4. Calculate Expenses
var monthlyTax = annualTax / 12;
var monthlyIns = annualInsurance / 12;
var totalMonthlyExpenses = monthlyMortgage + monthlyTax + monthlyIns + monthlyMaint + monthlyPM;
// 5. Calculate Returns
var monthlyCashFlow = monthlyRent – totalMonthlyExpenses;
var annualCashFlow = monthlyCashFlow * 12;
var cashOnCash = 0;
if (downPayment > 0) {
cashOnCash = (annualCashFlow / downPayment) * 100;
}
// 6. Display Results
document.getElementById('res-mortgage').innerHTML = "$" + monthlyMortgage.toFixed(2);
document.getElementById('res-expenses').innerHTML = "$" + totalMonthlyExpenses.toFixed(2);
var cfElement = document.getElementById('res-cashflow');
cfElement.innerHTML = "$" + monthlyCashFlow.toFixed(2);
if(monthlyCashFlow < 0) {
cfElement.className = "rp-result-value rp-negative";
} else {
cfElement.className = "rp-result-value rp-highlight";
}
var annualCfElement = document.getElementById('res-annual-cf');
annualCfElement.innerHTML = "$" + annualCashFlow.toFixed(2);
if(annualCashFlow < 0) {
annualCfElement.className = "rp-result-value rp-negative";
} else {
annualCfElement.className = "rp-result-value";
}
var cocElement = document.getElementById('res-coc');
cocElement.innerHTML = cashOnCash.toFixed(2) + "%";
if(cashOnCash < 0) {
cocElement.className = "rp-result-value rp-negative";
} else {
cocElement.className = "rp-result-value rp-highlight";
}
document.getElementById('rp-result-box').style.display = "block";
}
Understanding Rental Property Cash Flow Analysis
Investing in real estate is one of the most reliable ways to build wealth, but success hinges on the numbers. This Rental Property Cash Flow Calculator helps investors determine the viability of a potential investment property by analyzing income against expenses.
What is Positive Cash Flow?
Positive cash flow occurs when a property's gross rental income exceeds all operating expenses and debt service obligations. It represents the profit you pocket every month. Achieving positive cash flow ensures that the property pays for itself and provides passive income, reducing the risk of holding the asset.
Key Metrics Calculated
Net Operating Income (NOI): While not explicitly separated in the summary, this forms the basis of valuation. It is income minus operating expenses (excluding the mortgage).
Cash on Cash Return (CoC): This is a crucial ROI metric for real estate investors. It measures the annual pre-tax cash flow divided by the total cash invested (Down Payment). A good CoC return varies by market, but many investors target 8-12%.
Monthly Expenses: Accurate analysis requires accounting for "hidden" costs like vacancy, maintenance (CapEx), property management fees, and insurance, not just the mortgage payment.
How to Use This Calculator
Enter Purchase Details: Input the property price, your down payment, and loan details.
Estimate Income: Input the expected monthly rent. Check comparable listings (comps) in the area to ensure this figure is realistic.
Account for Expenses: Be honest about taxes, insurance, and maintenance. A common rule of thumb for maintenance is budgeting 1% of the property value per year or 10% of the rent.
Analyze the Result: If the Cash Flow is negative, the property is a liability. You will need to either negotiate a lower price, increase the down payment to lower the mortgage, or find ways to increase rental income.
Using a rental property calculator removes emotion from the buying decision, allowing you to focus purely on the mathematical return on investment.