function calculateCashFlow() {
// 1. Get Values
var price = parseFloat(document.getElementById('prop_price').value) || 0;
var down = parseFloat(document.getElementById('down_payment').value) || 0;
var rate = parseFloat(document.getElementById('int_rate').value) || 0;
var years = parseFloat(document.getElementById('loan_years').value) || 0;
var closing = parseFloat(document.getElementById('closing_costs').value) || 0;
var rent = parseFloat(document.getElementById('monthly_rent').value) || 0;
var vacancy = parseFloat(document.getElementById('vacancy_rate').value) || 0;
var taxYear = parseFloat(document.getElementById('prop_tax').value) || 0;
var insYear = parseFloat(document.getElementById('home_insurance').value) || 0;
var repairs = parseFloat(document.getElementById('repairs_mo').value) || 0;
var mgmt = parseFloat(document.getElementById('mgmt_fee').value) || 0;
// 2. Validate
if(price <= 0 || rent 0) {
mortgagePayment = loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, numPayments)) / (Math.pow(1 + monthlyRate, numPayments) – 1);
} else {
mortgagePayment = loanAmount / numPayments;
}
// 4. Calculate Operating Expenses
var monthlyTax = taxYear / 12;
var monthlyIns = insYear / 12;
var vacancyLoss = rent * (vacancy / 100);
var mgmtCost = rent * (mgmt / 100);
// Effective Income (Rent – Vacancy)
var effectiveIncome = rent – vacancyLoss;
// Total Expenses (Mortgage + Tax + Ins + Repairs + Mgmt)
var totalMonthlyExpenses = mortgagePayment + monthlyTax + monthlyIns + repairs + mgmtCost;
// 5. Calculate Cash Flow
var monthlyCashFlow = effectiveIncome – totalMonthlyExpenses;
var annualCashFlow = monthlyCashFlow * 12;
// 6. Calculate Cash on Cash Return
// Total Cash Invested = Down Payment + Closing Costs
var totalCashInvested = down + closing;
var cocReturn = 0;
if(totalCashInvested > 0) {
cocReturn = (annualCashFlow / totalCashInvested) * 100;
}
// 7. Update UI
var resDiv = document.getElementById('results');
resDiv.style.display = 'block';
// Helper for formatting
var fmtMoney = new Intl.NumberFormat('en-US', { style: 'currency', currency: 'USD' });
document.getElementById('res_mortgage').innerText = fmtMoney.format(mortgagePayment);
document.getElementById('res_expenses').innerText = fmtMoney.format(totalMonthlyExpenses);
document.getElementById('res_income').innerText = fmtMoney.format(effectiveIncome);
var cfEl = document.getElementById('res_cashflow');
cfEl.innerText = fmtMoney.format(monthlyCashFlow);
cfEl.className = monthlyCashFlow >= 0 ? "result-value positive" : "result-value negative";
var annCfEl = document.getElementById('res_annual_cashflow');
annCfEl.innerText = fmtMoney.format(annualCashFlow);
annCfEl.className = annualCashFlow >= 0 ? "result-value positive" : "result-value negative";
var cocEl = document.getElementById('res_coc');
cocEl.innerText = cocReturn.toFixed(2) + "%";
cocEl.className = cocReturn >= 0 ? "result-value positive" : "result-value negative";
}
Understanding Rental Property Cash Flow
Investing in real estate is a powerful way to build wealth, but the success of a rental property hinges on its ability to generate positive cash flow. This Rental Property Cash Flow Calculator helps investors determine if a potential deal will be profitable or a financial drain.
What is Cash Flow?
Cash flow is the net amount of money moving in and out of a rental property business. In simple terms, it is the money left over after all operating expenses and debt service (mortgage payments) have been paid from the collected rent.
Positive Cash Flow: Your income exceeds your expenses. This is the goal for most buy-and-hold investors.
Negative Cash Flow: Your expenses exceed your income. This means you must pay out of pocket every month to keep the property.
Key Metrics Calculated
This calculator breaks down several critical financial metrics for real estate investors:
NOI (Net Operating Income): This is your total income minus operating expenses (like taxes, insurance, and repairs) but excluding mortgage payments. It measures the raw profitability of the asset itself.
Cash on Cash Return (CoC): This is perhaps the most important metric for ROI. It is calculated by dividing your annual pre-tax cash flow by the total cash actually invested (Down Payment + Closing Costs). A CoC return of 8-12% is generally considered solid for residential rentals.
Vacancy Rate: No property is occupied 100% of the time. We include a vacancy provision (typically 5-10%) to account for turnover periods where you collect no rent.
How to Improve Cash Flow
If your calculation shows negative or low cash flow, consider these adjustments:
Increase Rent: Are you charging market rates? Small increases can significantly boost the bottom line.
Lower Expenses: Shop around for cheaper insurance or handle minor maintenance yourself to reduce contractor fees.
Larger Down Payment: Putting more money down reduces the loan amount and the monthly mortgage payment, instantly increasing monthly cash flow.
Why Use This Calculator?
Whether you are analyzing a single-family home, a duplex, or a condo, running the numbers strictly is vital. Emotions should never dictate an investment decision. By inputting accurate estimates for vacancy, repairs, and management fees, this tool provides a realistic view of the property's financial performance before you sign the closing papers.