function calculateCashFlow() {
// 1. Get Input Values
var price = parseFloat(document.getElementById('rpcPrice').value);
var down = parseFloat(document.getElementById('rpcDown').value);
var rate = parseFloat(document.getElementById('rpcRate').value);
var term = parseFloat(document.getElementById('rpcTerm').value);
var rent = parseFloat(document.getElementById('rpcRent').value);
var otherInc = parseFloat(document.getElementById('rpcOtherInc').value);
var taxYearly = parseFloat(document.getElementById('rpcTax').value);
var insYearly = parseFloat(document.getElementById('rpcIns').value);
var hoaMonthly = parseFloat(document.getElementById('rpcHoa').value);
var maintPercent = parseFloat(document.getElementById('rpcMaint').value);
// Error Handling
if (isNaN(price) || isNaN(down) || isNaN(rate) || isNaN(term) || isNaN(rent)) {
alert("Please enter valid numeric values for all fields.");
return;
}
// 2. Calculations
var loanAmount = price – down;
// Mortgage P&I Calculation
var monthlyRate = rate / 100 / 12;
var totalPayments = term * 12;
var monthlyPI = 0;
if (loanAmount > 0) {
if (rate === 0) {
monthlyPI = loanAmount / totalPayments;
} else {
monthlyPI = loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, totalPayments)) / (Math.pow(1 + monthlyRate, totalPayments) – 1);
}
}
// Operating Expenses
var monthlyTax = taxYearly / 12;
var monthlyIns = insYearly / 12;
var monthlyMaint = (rent * maintPercent) / 100;
var totalMonthlyExpenses = monthlyPI + monthlyTax + monthlyIns + hoaMonthly + monthlyMaint;
var totalMonthlyIncome = rent + otherInc;
var monthlyCashFlow = totalMonthlyIncome – totalMonthlyExpenses;
var yearlyCashFlow = monthlyCashFlow * 12;
// ROI Metrics
// Cash on Cash = Yearly Cash Flow / Total Cash Invested (assuming Down Payment is total investment here for simplicity)
var cashInvested = down;
var cocReturn = 0;
if (cashInvested > 0) {
cocReturn = (yearlyCashFlow / cashInvested) * 100;
}
// Cap Rate = NOI / Purchase Price
// NOI = Annual Income – Annual Operating Expenses (Excluding Mortgage P&I)
var annualOperatingExp = (monthlyTax + monthlyIns + hoaMonthly + monthlyMaint) * 12;
var annualIncome = totalMonthlyIncome * 12;
var noi = annualIncome – annualOperatingExp;
var capRate = 0;
if (price > 0) {
capRate = (noi / price) * 100;
}
// 3. Update DOM
document.getElementById('resMortgage').innerText = formatCurrency(monthlyPI);
document.getElementById('resTotalExp').innerText = formatCurrency(totalMonthlyExpenses);
var cfEl = document.getElementById('resMonthlyCF');
cfEl.innerText = formatCurrency(monthlyCashFlow);
cfEl.className = "rpc-result-value " + (monthlyCashFlow >= 0 ? "rpc-positive" : "rpc-negative");
var yCfEl = document.getElementById('resYearlyCF');
yCfEl.innerText = formatCurrency(yearlyCashFlow);
yCfEl.className = "rpc-result-value " + (yearlyCashFlow >= 0 ? "rpc-positive" : "rpc-negative");
document.getElementById('resCoc').innerText = cocReturn.toFixed(2) + "%";
document.getElementById('resCap').innerText = capRate.toFixed(2) + "%";
// Show Results
document.getElementById('rpcResults').style.display = "block";
}
function formatCurrency(num) {
return "$" + num.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
}
Understanding Rental Property Cash Flow Analysis
Investing in real estate is one of the most reliable ways to build long-term wealth, but success depends heavily on the numbers. A Rental Property Cash Flow Calculator is an essential tool for investors to determine if a potential property will be an asset or a liability. "Cash flow" represents the net amount of money moving in and out of a business—in this case, your rental property.
Positive cash flow means the property generates more income than it costs to own and operate, providing you with passive income. Negative cash flow means you are paying out of pocket to hold the property, which is generally sustainable only if significant appreciation is expected.
How to Interpret the Metrics
This calculator provides several key performance indicators (KPIs) to help you evaluate your investment:
Net Monthly Cash Flow: This is your "take-home" profit after the mortgage, taxes, insurance, and maintenance reserves are paid. Most investors aim for at least $100-$300 per door in positive monthly cash flow.
Cash on Cash Return (CoC): This measures the return on the actual cash you invested (down payment). It allows you to compare real estate returns against other investments like stocks or bonds. A CoC return of 8-12% is often considered a solid benchmark for rental properties.
Cap Rate (Capitalization Rate): This calculates the rate of return on the property based on the income the property is expected to generate, independent of financing. It helps compare properties regardless of how they are purchased (cash vs. loan).
Pro Tip: Always Account for Maintenance and Vacancy
New investors often make the mistake of calculating returns based only on rent minus the mortgage. This is dangerous. Real estate requires upkeep. You must allocate a percentage of rent (typically 5-10% for maintenance and 5% for vacancy) to ensure you have reserves when the roof leaks or a tenant moves out.
Improving Your Rental Property Returns
If the calculator shows a negative or low return, consider these strategies to improve the numbers:
Increase Income: Can you add amenities like laundry, parking, or storage? Small cosmetic upgrades can also justify higher rents.
Lower Expenses: Shop around for cheaper insurance or challenge your property tax assessment.
Adjust Financing: A larger down payment reduces the monthly mortgage burden, instantly improving monthly cash flow, though it may lower your Cash on Cash return percentage.
Use this calculator as a first-pass filter. If the numbers work here using conservative estimates, the property warrants a deeper due diligence process.