Investing in real estate is one of the most reliable ways to build wealth, but simply buying a property doesn't guarantee profit. The most critical metric for any buy-and-hold investor is Cash Flow. This calculator helps you analyze a potential rental property deal to determine if it meets your investment goals.
How This Calculator Works
Our Rental Property Calculator breaks down the deal into three main components: Acquisition, Income, and Expenses. By inputting accurate numbers, you can derive the following key performance indicators (KPIs):
Monthly Cash Flow: The profit remaining after all expenses and mortgage payments are made. Positive cash flow puts money in your pocket every month.
Net Operating Income (NOI): This is the total income minus operating expenses (excluding mortgage payments). It represents the profitability of the property itself, independent of financing.
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 ROI: This measures the return on the actual cash you invested (Down Payment + Closing Costs). It is calculated as Annual Cash Flow / Total Cash Invested.
Key Expenses to Consider
Many new investors underestimate expenses. When using this calculator, ensure you account for:
Vacancy Rate: Properties won't be rented 365 days a year. A standard assumption is 5-8% to account for turnover periods.
Maintenance & CapEx: Even if the house is new, things break. Setting aside 5-10% of rent for repairs and capital expenditures (like a new roof or HVAC) is prudent.
Property Management: If you hire a professional manager, expect to pay 8-10% of the monthly rent. If you self-manage, this is 0%, but costs you time.
Interpreting the Results
Is the Cash Flow Positive? If your result is red (negative), the property will cost you money every month to own. Unless you are banking solely on appreciation (a risky strategy), investors typically look for positive cash flow.
What is a Good ROI? While "good" is subjective, many real estate investors target a Cash on Cash ROI of 8-12% or higher, as this typically outperforms the stock market average while providing tangible asset ownership.
function calculateRental() {
// 1. Get Inputs
var price = parseFloat(document.getElementById('rpPrice').value) || 0;
var downPercent = parseFloat(document.getElementById('rpDown').value) || 0;
var interestRate = parseFloat(document.getElementById('rpIntRate').value) || 0;
var years = parseFloat(document.getElementById('rpTerm').value) || 0;
var closingCosts = parseFloat(document.getElementById('rpClosing').value) || 0;
var rent = parseFloat(document.getElementById('rpRent').value) || 0;
var annualTax = parseFloat(document.getElementById('rpTax').value) || 0;
var annualIns = parseFloat(document.getElementById('rpIns').value) || 0;
var monthlyHOA = parseFloat(document.getElementById('rpHOA').value) || 0;
var vacancyRate = parseFloat(document.getElementById('rpVacancy').value) || 0;
var maintRate = parseFloat(document.getElementById('rpMaint').value) || 0;
var mgmtRate = parseFloat(document.getElementById('rpMgmt').value) || 0;
// 2. Calculate Mortgage (Principal & Interest)
var downPaymentAmount = price * (downPercent / 100);
var loanAmount = price – downPaymentAmount;
var monthlyRate = (interestRate / 100) / 12;
var numberOfPayments = years * 12;
var monthlyMortgage = 0;
if (interestRate > 0 && years > 0) {
monthlyMortgage = loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments)) / (Math.pow(1 + monthlyRate, numberOfPayments) – 1);
} else if (years > 0) {
monthlyMortgage = loanAmount / numberOfPayments;
}
// 3. Calculate Monthly Expenses (Variable)
var monthlyVacancy = rent * (vacancyRate / 100);
var monthlyMaint = rent * (maintRate / 100);
var monthlyMgmt = rent * (mgmtRate / 100);
// 4. Calculate Fixed Monthly Expenses
var monthlyTax = annualTax / 12;
var monthlyIns = annualIns / 12;
// 5. Total Operating Expenses (Excluding Mortgage)
var monthlyOperatingExpenses = monthlyVacancy + monthlyMaint + monthlyMgmt + monthlyTax + monthlyIns + monthlyHOA;
// 6. Net Operating Income (NOI)
var monthlyNOI = rent – monthlyOperatingExpenses;
var annualNOI = monthlyNOI * 12;
// 7. Total Expenses (Including Mortgage)
var totalMonthlyExpenses = monthlyOperatingExpenses + monthlyMortgage;
// 8. Cash Flow
var monthlyCashFlow = rent – totalMonthlyExpenses;
var annualCashFlow = monthlyCashFlow * 12;
// 9. Returns
var totalCashInvested = downPaymentAmount + closingCosts;
var capRate = (price > 0) ? (annualNOI / price) * 100 : 0;
var cashOnCash = (totalCashInvested > 0) ? (annualCashFlow / totalCashInvested) * 100 : 0;
// 10. Update UI
// Helper for currency
var fmt = new Intl.NumberFormat('en-US', { style: 'currency', currency: 'USD' });
document.getElementById('resMortgage').innerText = fmt.format(monthlyMortgage);
document.getElementById('resExpenses').innerText = fmt.format(totalMonthlyExpenses);
document.getElementById('resNOI').innerText = fmt.format(annualNOI);
var cfEl = document.getElementById('resCashFlow');
cfEl.innerText = fmt.format(monthlyCashFlow);
// Styling for positive/negative cash flow
if (monthlyCashFlow >= 0) {
cfEl.classList.remove('rp-negative');
cfEl.classList.add('rp-highlight');
} else {
cfEl.classList.remove('rp-highlight');
cfEl.classList.add('rp-negative');
}
document.getElementById('resCapRate').innerText = capRate.toFixed(2) + "%";
var cocEl = document.getElementById('resCoC');
cocEl.innerText = cashOnCash.toFixed(2) + "%";
if (cashOnCash < 0) {
cocEl.classList.add('rp-negative');
} else {
cocEl.classList.remove('rp-negative');
}
}
// Initialize on load
window.onload = function() {
calculateRental();
};