function calculateCashFlow() {
// 1. Get Values
var price = parseFloat(document.getElementById('purchasePrice').value);
var down = parseFloat(document.getElementById('downPayment').value);
var rate = parseFloat(document.getElementById('interestRate').value);
var term = parseFloat(document.getElementById('loanTerm').value);
var rent = parseFloat(document.getElementById('monthlyRent').value);
var otherInc = parseFloat(document.getElementById('otherIncome').value);
var opExp = parseFloat(document.getElementById('monthlyExpenses').value);
// 2. Validation
if (isNaN(price) || isNaN(down) || isNaN(rate) || isNaN(term) || isNaN(rent) || isNaN(opExp)) {
alert("Please fill in all required fields with valid numbers.");
return;
}
// Handle empty other income
if (isNaN(otherInc)) otherInc = 0;
// 3. Loan Calculations
var loanAmount = price – down;
var monthlyRate = (rate / 100) / 12;
var numPayments = term * 12;
var monthlyMortgage = 0;
if (rate > 0) {
monthlyMortgage = loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, numPayments)) / (Math.pow(1 + monthlyRate, numPayments) – 1);
} else {
monthlyMortgage = loanAmount / numPayments;
}
// 4. Expense & Income Calculations
var totalMonthlyIncome = rent + otherInc;
var totalMonthlyExpenses = monthlyMortgage + opExp;
var monthlyCashFlow = totalMonthlyIncome – totalMonthlyExpenses;
var annualCashFlow = monthlyCashFlow * 12;
// 5. Advanced Metrics
// NOI = (Income – Operating Expenses) * 12. Excludes Debt Service (Mortgage).
var annualNOI = (totalMonthlyIncome – opExp) * 12;
// Cap Rate = (NOI / Purchase Price) * 100
var capRate = (annualNOI / price) * 100;
// Cash on Cash Return = (Annual Cash Flow / Total Cash Invested) * 100
// Using Down Payment as proxy for total cash invested for simplicity
var cashOnCash = 0;
if (down > 0) {
cashOnCash = (annualCashFlow / down) * 100;
}
// 6. Formatting Helpers
function formatCurrency(num) {
return "$" + num.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
}
function formatPercent(num) {
return num.toFixed(2) + "%";
}
// 7. Display Results
document.getElementById('resultsArea').style.display = 'block';
document.getElementById('resMortgage').innerText = formatCurrency(monthlyMortgage);
document.getElementById('resTotalExpenses').innerText = formatCurrency(totalMonthlyExpenses);
document.getElementById('resNOI').innerText = formatCurrency(annualNOI);
var flowEl = document.getElementById('resCashFlow');
flowEl.innerText = formatCurrency(monthlyCashFlow);
if (monthlyCashFlow >= 0) {
flowEl.className = "result-value positive-flow";
} else {
flowEl.className = "result-value negative-flow";
}
document.getElementById('resCapRate').innerText = formatPercent(capRate);
var cocEl = document.getElementById('resCoC');
cocEl.innerText = formatPercent(cashOnCash);
if (cashOnCash >= 0) {
cocEl.className = "result-value positive-flow";
} else {
cocEl.className = "result-value negative-flow";
}
}
Understanding Rental Property Cash Flow
Investing in real estate is a powerful way to build wealth, but the success of any rental property hinges on the numbers. This Rental Property Cash Flow Calculator helps investors analyze potential deals by determining the monthly income remaining after all expenses are paid.
How the Calculation Works
To accurately calculate your potential returns, this tool considers several key financial factors:
Net Operating Income (NOI): This is your total annual rental income minus all operating expenses (taxes, insurance, maintenance, management fees), excluding the mortgage payment. It represents the profitability of the property before debt.
Cash Flow: This is the net profit you pocket every month. It is calculated by taking the NOI and subtracting your mortgage payment (debt service). Positive cash flow means the property is paying for itself and generating income.
Cap Rate (Capitalization Rate): Calculated as NOI / Purchase Price. This percentage allows you to compare the profitability of different properties regardless of how they are financed.
Cash on Cash Return (CoC): This measures the return on the actual cash you invested (down payment). It is calculated as Annual Cash Flow / Total Cash Invested.
Real World Example
Let's say you are looking to purchase a single-family home to rent out.
Purchase Price: $200,000
Down Payment: $50,000 (25%)
Interest Rate: 6.5% on a 30-year fixed loan
Rental Income: $2,000 per month
Operating Expenses: $600 per month (Taxes, Insurance, Repairs)
Using the calculator above, your estimated monthly mortgage payment would be roughly $948. Your total monthly expenses (Mortgage + Operating) would be $1,548.
Your Monthly Cash Flow would be: $2,000 (Rent) – $1,548 (Expenses) = $452 per month. This results in a Cash on Cash return of roughly 10.8%, making it a potentially attractive investment.
Why is Cash Flow Important?
Positive cash flow provides a buffer against vacancies and repairs. While appreciation (the property increasing in value) is a great bonus, seasoned investors rely on cash flow to sustain their business. A property with negative cash flow is a liability that costs you money every month to hold.