function calculateRental() {
// 1. Get Input Values
var price = parseFloat(document.getElementById('purchasePrice').value);
var downPercent = parseFloat(document.getElementById('downPaymentPercent').value);
var intRate = parseFloat(document.getElementById('interestRate').value);
var termYears = parseFloat(document.getElementById('loanTerm').value);
var closingCosts = parseFloat(document.getElementById('closingCosts').value);
var grossRent = parseFloat(document.getElementById('monthlyRent').value);
var vacancyPercent = parseFloat(document.getElementById('vacancyRate').value);
var propTax = parseFloat(document.getElementById('propertyTax').value);
var insurance = parseFloat(document.getElementById('insurance').value);
var maintenance = parseFloat(document.getElementById('maintenance').value);
// Validation
if (isNaN(price) || isNaN(grossRent) || isNaN(intRate)) {
alert("Please enter valid numbers in all fields.");
return;
}
// 2. Calculations
// Loan Calculations
var downPaymentAmount = price * (downPercent / 100);
var loanAmount = price – downPaymentAmount;
var monthlyInterest = (intRate / 100) / 12;
var numberOfPayments = termYears * 12;
var mortgagePayment = 0;
if (intRate === 0) {
mortgagePayment = loanAmount / numberOfPayments;
} else {
mortgagePayment = loanAmount * (monthlyInterest * Math.pow(1 + monthlyInterest, numberOfPayments)) / (Math.pow(1 + monthlyInterest, numberOfPayments) – 1);
}
// Income Calculations
var vacancyLoss = grossRent * (vacancyPercent / 100);
var effectiveMonthlyIncome = grossRent – vacancyLoss;
var annualEffectiveIncome = effectiveMonthlyIncome * 12;
// Expense Calculations
var totalMonthlyOperatingExpenses = propTax + insurance + maintenance; // Excluding mortgage
var totalAnnualOperatingExpenses = totalMonthlyOperatingExpenses * 12;
// Net Operating Income (NOI)
var annualNOI = annualEffectiveIncome – totalAnnualOperatingExpenses;
// Cash Flow
var totalMonthlyOutflow = totalMonthlyOperatingExpenses + mortgagePayment;
var monthlyCashFlow = effectiveMonthlyIncome – totalMonthlyOutflow;
var annualCashFlow = monthlyCashFlow * 12;
// Investment Returns
var totalInitialInvestment = downPaymentAmount + closingCosts;
var cashOnCashReturn = (annualCashFlow / totalInitialInvestment) * 100;
var capRate = (annualNOI / price) * 100;
// 3. Display Results
document.getElementById('resultsArea').style.display = 'block';
// Helper for formatting currency
var fmt = new Intl.NumberFormat('en-US', { style: 'currency', currency: 'USD' });
document.getElementById('resCashFlow').innerHTML = fmt.format(monthlyCashFlow);
document.getElementById('resCashFlow').style.color = monthlyCashFlow >= 0 ? '#27ae60' : '#c0392b';
document.getElementById('resCoC').innerHTML = cashOnCashReturn.toFixed(2) + "%";
document.getElementById('resCapRate').innerHTML = capRate.toFixed(2) + "%";
document.getElementById('resIncome').innerHTML = fmt.format(effectiveMonthlyIncome);
document.getElementById('resMortgage').innerHTML = fmt.format(mortgagePayment);
document.getElementById('resExpenses').innerHTML = fmt.format(totalMonthlyOperatingExpenses);
document.getElementById('resNOI').innerHTML = fmt.format(annualNOI);
}
Mastering Rental Property Analysis
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. Successful real estate investing relies heavily on running the numbers accurately before making an offer. This Rental Property Cash Flow Calculator helps you evaluate the financial viability of a potential investment property by breaking down income, expenses, and key return on investment (ROI) metrics.
Understanding Key Metrics
1. Cash Flow
Cash flow is the net amount of cash moving into or out of your investment each month. It is calculated by taking your gross rental income and subtracting all expenses, including the mortgage payment, taxes, insurance, and maintenance. Positive cash flow means the property is putting money in your pocket every month, while negative cash flow means you are paying out of pocket to hold the asset.
2. Cash on Cash Return (CoC)
This metric measures the annual return you made on the actual cash you invested (Down Payment + Closing Costs). Unlike a standard ROI calculation which might look at the total loan value, CoC Return focuses strictly on the efficiency of the capital you deployed. A CoC return of 8-12% is generally considered a strong target for rental properties.
3. Cap Rate (Capitalization Rate)
The Cap Rate measures the natural rate of return of the property assuming you bought it with all cash (no loan). It is calculated by dividing the Net Operating Income (NOI) by the Property Price. This metric allows you to compare properties apples-to-apples without the influence of mortgage interest rates or financing terms.
How to Use This Calculator
To get the most accurate results, ensure you are realistic with your expense estimates:
Vacancy Rate: Always account for the property sitting empty between tenants. A standard conservative estimate is 5-8%.
Maintenance: Even if a house is new, things break. Set aside 10-15% of the rent for future repairs.
Operating Expenses: Don't forget property taxes, landlord insurance, and HOA fees if applicable.
By adjusting the "Down Payment" and "Purchase Price" fields, you can determine exactly what offer price makes the deal profitable for your specific financial goals.