function calculateRental() {
// Get Input Values
var price = parseFloat(document.getElementById('rp_price').value);
var downPerc = parseFloat(document.getElementById('rp_down').value);
var interestRate = parseFloat(document.getElementById('rp_interest').value);
var termYears = parseFloat(document.getElementById('rp_term').value);
var rent = parseFloat(document.getElementById('rp_rent').value);
var taxYearly = parseFloat(document.getElementById('rp_tax').value);
var insuranceYearly = parseFloat(document.getElementById('rp_insurance').value);
var maintMonthly = parseFloat(document.getElementById('rp_maintenance').value);
// Validation
if (isNaN(price) || isNaN(rent)) {
alert("Please enter valid numbers for Price and Rent.");
return;
}
// Calculations
var downPaymentAmount = price * (downPerc / 100);
var loanAmount = price – downPaymentAmount;
// Mortgage Calculation
var monthlyRate = (interestRate / 100) / 12;
var totalMonths = termYears * 12;
var monthlyMortgage = 0;
if (interestRate === 0) {
monthlyMortgage = loanAmount / totalMonths;
} else {
monthlyMortgage = loanAmount * (monthlyRate * Math.pow((1 + monthlyRate), totalMonths)) / (Math.pow((1 + monthlyRate), totalMonths) – 1);
}
// Expense Calculations
var monthlyTax = taxYearly / 12;
var monthlyInsurance = insuranceYearly / 12;
var totalMonthlyExpenses = monthlyMortgage + monthlyTax + monthlyInsurance + maintMonthly;
// Cash Flow
var monthlyCashFlow = rent – totalMonthlyExpenses;
var annualCashFlow = monthlyCashFlow * 12;
// Cash on Cash Return (Simple: Annual Cash Flow / Down Payment)
// Note: Excluding closing costs for simplicity in this specific calc logic, or assume included in down payment input context
var cocReturn = 0;
if (downPaymentAmount > 0) {
cocReturn = (annualCashFlow / downPaymentAmount) * 100;
}
// Display Results
document.getElementById('results').style.display = 'block';
document.getElementById('res_loan').innerText = "$" + loanAmount.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('res_mortgage').innerText = "$" + monthlyMortgage.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('res_expenses').innerText = "$" + totalMonthlyExpenses.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
var cfElement = document.getElementById('res_cashflow');
cfElement.innerText = "$" + monthlyCashFlow.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
if (monthlyCashFlow >= 0) {
cfElement.className = "result-value positive-cashflow";
} else {
cfElement.className = "result-value negative-cashflow";
}
var cocElement = document.getElementById('res_coc');
cocElement.innerText = cocReturn.toFixed(2) + "%";
if (cocReturn >= 0) {
cocElement.style.color = "#28a745";
} else {
cocElement.style.color = "#dc3545";
}
}
How to Analyze a Rental Property Investment
Investing in real estate is one of the most reliable ways to build wealth, but simply buying a property and renting it out doesn't guarantee a profit. To succeed, investors must meticulously analyze the numbers. This Rental Property Calculator helps you determine the viability of a potential investment by breaking down income, expenses, and returns.
Understanding Cash Flow
Cash flow is the net amount of money moving in and out of a business. In real estate, it is the money remaining after all operating expenses and mortgage payments have been made. A property with positive cash flow puts money in your pocket every month, while negative cash flow requires you to pay out of pocket to keep the property running.
Ideally, you want a property that generates positive cash flow to cover unforeseen repairs and vacancies while providing passive income.
Key Metrics: Cash on Cash Return
This calculator focuses heavily on Cash on Cash (CoC) Return. This metric measures the annual return on the actual cash invested in the property. It is calculated as:
Cash on Cash Return = (Annual Pre-Tax Cash Flow / Total Cash Invested) x 100%
Unlike a standard ROI (Return on Investment) which might look at the total loan value, CoC Return tells you how hard your specific down payment dollars are working. A CoC return of 8-12% is generally considered solid for residential real estate, though this varies by market.
Estimating Expenses Correctly
One of the biggest mistakes new investors make is underestimating expenses. Beyond the mortgage (Principal & Interest), you must account for:
- Property Taxes: These can vary significantly by county.
- Insurance: Landlord policies are often more expensive than homeowner policies.
- Maintenance & CapEx: Roofs, HVACs, and water heaters eventually break. Budgeting 10-15% of rent for maintenance is a prudent rule of thumb.
- Vacancy: Your property won't be rented 365 days a year. Factoring in a 5-8% vacancy rate ensures you aren't caught off guard during turnover periods.
How to Use This Calculator
Start by entering the Purchase Price and your financing details, including Down Payment % and Interest Rate. Next, input the expected Monthly Rental Income based on comparable properties in the neighborhood.
Be honest with your expense inputs. Enter the annual property tax and insurance costs, along with a monthly budget for maintenance or HOA fees. Click "Calculate Cash Flow" to see if the deal makes financial sense. If the Cash Flow is red, you may need to negotiate a lower price or find a property with higher rental potential.