function calculateCashFlow() {
// Get Input Values
var monthlyRent = parseFloat(document.getElementById("monthlyRent").value) || 0;
var otherIncome = parseFloat(document.getElementById("otherIncome").value) || 0;
var mortgagePayment = parseFloat(document.getElementById("mortgagePayment").value) || 0;
var propertyTax = parseFloat(document.getElementById("propertyTax").value) || 0;
var insurance = parseFloat(document.getElementById("insurance").value) || 0;
var hoaFee = parseFloat(document.getElementById("hoaFee").value) || 0;
var vacancyRate = parseFloat(document.getElementById("vacancyRate").value) || 0;
var managementFee = parseFloat(document.getElementById("managementFee").value) || 0;
var repairsCapex = parseFloat(document.getElementById("repairsCapex").value) || 0;
// Income Calculations
var grossPotentialIncome = monthlyRent + otherIncome;
// Variable Expense Calculations (Percentages are based on Rent usually, but sometimes Gross. We'll use Gross Potential)
var vacancyCost = grossPotentialIncome * (vacancyRate / 100);
var managementCost = grossPotentialIncome * (managementFee / 100);
var repairsCost = grossPotentialIncome * (repairsCapex / 100);
// Total Income after Vacancy (Effective Gross Income)
var effectiveGrossIncome = grossPotentialIncome – vacancyCost;
// Total Expenses
// Fixed: Mortgage + Tax + Insurance + HOA
// Variable: Management + Repairs (Vacancy is usually deducted from income, but effectively reduces cash flow)
// Standard Cash Flow Formula: Income – Vacancy – Operating Expenses – Debt Service
var totalFixedExpenses = propertyTax + insurance + hoaFee;
var totalVariableExpenses = managementCost + repairsCost;
var totalOperatingExpenses = totalFixedExpenses + totalVariableExpenses; // Excluding mortgage
var netOperatingIncome = effectiveGrossIncome – totalOperatingExpenses;
var monthlyCashFlow = netOperatingIncome – mortgagePayment;
var annualCashFlow = monthlyCashFlow * 12;
// Total Expenses for display (Operating + Debt + Vacancy Cost contextually)
// For simple display, let's sum everything leaving your pocket or lost potential
var totalExpensesDisplay = totalOperatingExpenses + mortgagePayment + vacancyCost;
// Display Results
var resultDiv = document.getElementById("results");
resultDiv.style.display = "block";
document.getElementById("displayGrossIncome").innerText = "$" + grossPotentialIncome.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("displayTotalExpenses").innerText = "$" + totalExpensesDisplay.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("displayNOI").innerText = "$" + netOperatingIncome.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
var cfElement = document.getElementById("displayCashFlow");
cfElement.innerText = "$" + monthlyCashFlow.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
// Color coding
if (monthlyCashFlow >= 0) {
cfElement.className = "result-value positive-cf";
} else {
cfElement.className = "result-value negative-cf";
}
var annualCfElement = document.getElementById("displayAnnualCashFlow");
annualCfElement.innerText = "$" + annualCashFlow.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
if (annualCashFlow >= 0) {
annualCfElement.className = "result-value positive-cf";
} else {
annualCfElement.className = "result-value negative-cf";
}
}
How to Calculate Rental Property Cash Flow
Investing in real estate is one of the most reliable ways to build wealth, but simply buying a property doesn't guarantee a profit. The lifeblood of any rental investment is Cash Flow—the net amount of money left in your pocket after all expenses are paid. Using a Rental Property Cash Flow Calculator is essential for investors to evaluate a deal objectively before signing any papers.
What is Rental Cash Flow?
Cash flow is the difference between your rental income and the expenses associated with owning and managing the property. Positive cash flow means the property generates income for you every month. Negative cash flow means you are paying out of pocket to keep the property running.
The basic formula is:
Gross Income – Vacancy – Operating Expenses – Debt Service = Cash Flow
Key Inputs for Accurate Calculation
To get an accurate result from the calculator above, you need to understand the inputs:
1. Gross Income
This includes the monthly rent you charge tenants plus any additional income sources, such as coin-operated laundry machines, covered parking fees, or pet fees.
2. Vacancy Rate
No property is occupied 100% of the time. Tenants move out, and it takes time to clean, repair, and market the unit. A standard vacancy rate to estimate is 5% to 8%, depending on your local market demand.
3. Operating Expenses
These are the costs to keep the property running, excluding the mortgage. Common mistakes include underestimating these costs.
Property Management: Even if you self-manage, you should account for your time. Professional managers typically charge 8-10% of the rent.
Repairs & CapEx: Things break. You should set aside 5-10% of rent for routine repairs (leaky faucets) and Capital Expenditures (new roof, HVAC replacement).
Taxes & Insurance: These are non-negotiable fixed costs that usually increase over time.
Understanding the Results
Net Operating Income (NOI): This is the profitability of the property before factoring in the mortgage. It is useful for comparing properties regardless of financing.
Cash Flow: This is your actual "take-home" money. Most investors aim for at least $100-$200 per door in positive monthly cash flow for a buy-and-hold investment.
Why Cash Flow Matters
Properties with strong positive cash flow provide a safety net during economic downturns. If property values drop, a cash-flowing property still pays for itself and provides income. Conversely, a property with negative cash flow relies entirely on appreciation (the value going up) to make a profit, which is a much riskier speculation strategy.
Use this calculator to stress-test your investment. What happens if vacancy rises to 10%? What if you need to lower the rent? adjusting these numbers will help you make a confident, data-driven investment decision.