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Understanding Rental Property Cash Flow
Cash flow is the lifeblood of any real estate investment. It represents the net amount of cash moving in or out of a rental property business after all expenses and mortgage payments have been handled. A positive cash flow indicates that the property is generating income, while negative cash flow means the property is costing you money to hold.
Using a Rental Property Cash Flow Calculator helps investors evaluate whether a potential deal makes financial sense before signing the dotted line. By inputting realistic income and expense projections, you can avoid costly mistakes.
How is Cash Flow Calculated?
The basic formula for real estate cash flow is simple, yet requires accuracy in its components:
- Gross Income: Total rent collected plus other income (laundry, parking).
- Operating Expenses: Costs to run the property (Taxes, Insurance, HOA, Maintenance, Management, Vacancy).
- Net Operating Income (NOI): Gross Income minus Operating Expenses.
- Debt Service: Your monthly mortgage principal and interest payment.
- Cash Flow: NOI minus Debt Service.
Key Metrics in This Calculator
Cash on Cash Return (CoC)
Cash on Cash return measures the annual return you made on the property in relation to the amount of mortgage paid during the same year. It is one of the most important metrics because it tells you how hard your actual cash investment is working.
Formula: Annual Cash Flow / Total Cash Invested
Note: Our calculator estimates closing costs at 3% of the purchase price to calculate the total cash invested.
Cap Rate (Capitalization Rate)
The Cap Rate indicates the rate of return that is expected to be generated on a real estate investment property. It is based on the Net Operating Income (NOI) that the property is expected to generate.
Formula: NOI / Purchase Price
Example Scenario
Imagine purchasing a property for $200,000 with 20% down. If you rent it for $2,000/month and your total expenses (including mortgage, taxes, and repairs) come to $1,700/month, your monthly cash flow is $300.
This results in an annual cash flow of $3,600. If your initial cash investment (down payment + closing costs) was around $46,000, your Cash on Cash return would be roughly 7.8%.
Why Factor in Vacancy and Maintenance?
Novice investors often make the mistake of assuming a property will be rented 100% of the time and nothing will break. This calculator includes inputs for:
- Vacancy Rate: A standard conservative estimate is 5-8% (about 2-3 weeks of vacancy per year).
- Maintenance: Setting aside 5-10% of monthly rent for future repairs (roof, HVAC, plumbing) ensures you aren't caught off guard by large capital expenditures.
function calculateCashFlow() {
// 1. Get Input Values
var price = parseFloat(document.getElementById('purchasePrice').value);
var downPaymentPct = parseFloat(document.getElementById('downPayment').value);
var interestRate = parseFloat(document.getElementById('interestRate').value);
var loanTerm = parseFloat(document.getElementById('loanTerm').value);
var rent = parseFloat(document.getElementById('monthlyRent').value);
var vacancyPct = parseFloat(document.getElementById('vacancyRate').value);
var taxYearly = parseFloat(document.getElementById('propertyTax').value);
var insuranceYearly = parseFloat(document.getElementById('insurance').value);
var maintPct = parseFloat(document.getElementById('maintenance').value);
var hoaMonthly = parseFloat(document.getElementById('hoaFees').value);
// Validation
if (isNaN(price) || isNaN(downPaymentPct) || isNaN(interestRate) || isNaN(loanTerm) || isNaN(rent)) {
alert("Please fill in all required fields with valid numbers.");
return;
}
// 2. Calculate Mortgage (P & I)
var downPaymentAmt = price * (downPaymentPct / 100);
var loanAmount = price – downPaymentAmt;
var monthlyRate = (interestRate / 100) / 12;
var numberOfPayments = loanTerm * 12;
var monthlyMortgage = 0;
if (interestRate > 0) {
monthlyMortgage = loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments)) / (Math.pow(1 + monthlyRate, numberOfPayments) – 1);
} else {
monthlyMortgage = loanAmount / numberOfPayments;
}
// 3. Calculate Monthly Operating Expenses
var vacancyCost = rent * (vacancyPct / 100);
var maintCost = rent * (maintPct / 100);
var taxMonthly = taxYearly / 12;
var insuranceMonthly = insuranceYearly / 12;
var totalOperatingExpensesMonthly = vacancyCost + maintCost + taxMonthly + insuranceMonthly + hoaMonthly;
// 4. Calculate NOI & Cash Flow
var effectiveGrossIncome = rent – vacancyCost; // Rent minus vacancy loss
var noiMonthly = effectiveGrossIncome – (maintCost + taxMonthly + insuranceMonthly + hoaMonthly);
var totalExpensesMonthly = totalOperatingExpensesMonthly + monthlyMortgage;
var monthlyCashFlow = rent – totalExpensesMonthly; // Using Gross Rent – All Cash Outflows
// Re-adjusting logic for display:
// Often Cash Flow = (Rent – Vacancy) – (OpEx + Mortgage)
monthlyCashFlow = effectiveGrossIncome – (maintCost + taxMonthly + insuranceMonthly + hoaMonthly) – monthlyMortgage;
var annualCashFlow = monthlyCashFlow * 12;
var annualNOI = noiMonthly * 12;
// 5. Advanced Metrics
// Estimate Closing Costs at 3%
var closingCosts = price * 0.03;
var totalCashInvested = downPaymentAmt + closingCosts;
var cocReturn = (annualCashFlow / totalCashInvested) * 100;
var capRate = (annualNOI / price) * 100;
// 6. Display Results
// Helper to format currency
var fmt = new Intl.NumberFormat('en-US', { style: 'currency', currency: 'USD' });
document.getElementById('resIncome').innerHTML = fmt.format(effectiveGrossIncome);
document.getElementById('resMortgage').innerHTML = fmt.format(monthlyMortgage);
document.getElementById('resExpenses').innerHTML = fmt.format(totalOperatingExpensesMonthly + monthlyMortgage); // OpEx + Mortgage
var cfEl = document.getElementById('resMonthlyCashFlow');
cfEl.innerHTML = fmt.format(monthlyCashFlow);
cfEl.style.color = monthlyCashFlow >= 0 ? '#27ae60' : '#c0392b';
var acfEl = document.getElementById('resAnnualCashFlow');
acfEl.innerHTML = fmt.format(annualCashFlow);
acfEl.style.color = annualCashFlow >= 0 ? '#27ae60' : '#c0392b';
document.getElementById('resNOI').innerHTML = fmt.format(annualNOI);
document.getElementById('resCapRate').innerHTML = capRate.toFixed(2) + "%";
var cocEl = document.getElementById('resCOC');
cocEl.innerHTML = cocReturn.toFixed(2) + "%";
cocEl.style.color = cocReturn >= 0 ? '#333' : '#c0392b';
document.getElementById('resultsSection').style.display = 'block';
// Scroll to results
document.getElementById('resultsSection').scrollIntoView({ behavior: 'smooth' });
}