function calculateRentalCashFlow() {
// 1. Get Inputs
var price = parseFloat(document.getElementById('rpcPrice').value) || 0;
var downPercent = parseFloat(document.getElementById('rpcDown').value) || 0;
var rate = parseFloat(document.getElementById('rpcRate').value) || 0;
var term = parseFloat(document.getElementById('rpcTerm').value) || 30;
var closing = parseFloat(document.getElementById('rpcClosing').value) || 0;
var rent = parseFloat(document.getElementById('rpcRent').value) || 0;
var taxYear = parseFloat(document.getElementById('rpcTax').value) || 0;
var insYear = parseFloat(document.getElementById('rpcIns').value) || 0;
var hoaMonth = parseFloat(document.getElementById('rpcHoa').value) || 0;
var vacPercent = parseFloat(document.getElementById('rpcVacancy').value) || 0;
var maintPercent = parseFloat(document.getElementById('rpcMaint').value) || 0;
// 2. Calculate Mortgage (P&I)
var downAmount = price * (downPercent / 100);
var loanAmount = price – downAmount;
var monthlyRate = (rate / 100) / 12;
var totalMonths = term * 12;
var mortgage = 0;
if (monthlyRate > 0) {
mortgage = (loanAmount * monthlyRate) / (1 – Math.pow(1 + monthlyRate, -totalMonths));
} else {
mortgage = loanAmount / totalMonths;
}
// 3. Calculate Monthly Expenses
var monthlyTax = taxYear / 12;
var monthlyIns = insYear / 12;
var vacancyCost = rent * (vacPercent / 100);
var maintCost = rent * (maintPercent / 100);
var totalExpenses = mortgage + monthlyTax + monthlyIns + hoaMonth + vacancyCost + maintCost;
var operatingExpenses = monthlyTax + monthlyIns + hoaMonth + vacancyCost + maintCost; // Excluding mortgage for Cap Rate
// 4. Calculate Results
var cashFlow = rent – totalExpenses;
var annualCashFlow = cashFlow * 12;
var totalInvested = downAmount + closing;
// Cash on Cash ROI
var cocRoi = 0;
if (totalInvested > 0) {
cocRoi = (annualCashFlow / totalInvested) * 100;
}
// Cap Rate = (NOI / Price) * 100
// NOI = Annual Income – Annual Operating Expenses (Excluding Financing)
var annualNOI = (rent * 12) – (operatingExpenses * 12);
var capRate = 0;
if (price > 0) {
capRate = (annualNOI / price) * 100;
}
// 5. Update UI
document.getElementById('resCashFlow').innerText = formatCurrency(cashFlow);
if(cashFlow >= 0) {
document.getElementById('resCashFlow').className = 'value positive';
} else {
document.getElementById('resCashFlow').className = 'value negative';
}
document.getElementById('resCoc').innerText = cocRoi.toFixed(2) + '%';
document.getElementById('resCap').innerText = capRate.toFixed(2) + '%';
document.getElementById('resExp').innerText = formatCurrency(totalExpenses);
document.getElementById('bdIncome').innerText = '+ ' + formatCurrency(rent);
document.getElementById('bdMortgage').innerText = '- ' + formatCurrency(mortgage);
document.getElementById('bdTax').innerText = '- ' + formatCurrency(monthlyTax);
document.getElementById('bdIns').innerText = '- ' + formatCurrency(monthlyIns);
document.getElementById('bdHoa').innerText = '- ' + formatCurrency(hoaMonth);
document.getElementById('bdVacancy').innerText = '- ' + formatCurrency(vacancyCost);
document.getElementById('bdMaint').innerText = '- ' + formatCurrency(maintCost);
document.getElementById('bdTotal').innerText = formatCurrency(cashFlow);
// Show Results
document.getElementById('rpcResults').classList.add('active');
}
function formatCurrency(num) {
return '$' + num.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
}
Rental Property Cash Flow Calculator
Investing in real estate is one of the most reliable ways to build wealth, but the difference between a profitable asset and a financial burden lies in the math. This Rental Property Cash Flow Calculator helps investors accurately project the financial performance of potential rental properties before signing on the dotted line.
Why Calculating Cash Flow is Critical
Cash flow is the net amount of money moving into or out of your rental property business after all expenses and mortgage payments are made. Positive cash flow means the property pays for itself and generates profit, while negative cash flow means you are paying out of pocket to hold the asset.
While property appreciation (increase in value over time) is a great bonus, successful investors prioritize cash flow to ensure the investment is sustainable in the short term. Using a robust calculator ensures you account for "hidden" costs like vacancy and maintenance, which novice investors often overlook.
Key Metrics Explained
1. Cash on Cash ROI (Return on Investment)
This is arguably the most important metric for rental investors. It measures the annual return on the actual cash you invested (down payment + closing costs), rather than the total purchase price. A good Cash on Cash ROI typically ranges from 8% to 12%, though this varies by market.
The Cap Rate helps you compare the profitability of different properties irrespective of how they are financed (cash vs. mortgage). It represents the return on investment if you bought the property entirely with cash.
Formula: (Net Operating Income / Purchase Price) × 100
3. The 50% Rule
A quick rule of thumb used by investors is the 50% rule, which estimates that 50% of your rental income will go toward operating expenses (taxes, insurance, repairs, vacancy) excluding the mortgage payment. While our calculator provides a precise breakdown, the 50% rule is a good quick check.
How to Use This Calculator
To get the most accurate results, input the following data points:
Purchase Price & Loan Details: The total cost of the home and your financing terms.
Rental Income: Conservative estimate of monthly rent based on comparable properties (comps).
Vacancy Rate: The percentage of time the property sits empty. 5-8% is a standard industry average.
Maintenance & CapEx: Money set aside for repairs and big-ticket items like roof replacement. Setting aside 5-10% is recommended.
Frequently Asked Questions
What is a good cash flow for a rental property?
Most investors aim for at least $100 to $200 per unit per month in pure positive cash flow. However, some prioritize high appreciation potential and may accept lower monthly cash flow.
Should I include vacancy and maintenance costs?
Yes. Even if a property is new or currently rented, you will eventually face repairs and tenant turnover. Excluding these costs leads to inflated profit projections that aren't realistic.
What is the difference between ROI and Cap Rate?
Cap Rate measures the property's natural profitability unleveraged (as if bought with cash), whereas ROI (Cash on Cash) measures the return on your specific cash investment, factoring in the power of leverage (mortgage).
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