Rental Property Cash Flow Calculator
Analyze the potential profitability of a real estate investment by calculating monthly cash flow, taking into account income, fixed costs, and often-overlooked variable expenses like vacancy and CapEx.
Cash Flow Analysis
Gross Monthly Income:
$0.00
– Total Monthly Expenses:
$0.00
Monthly Cash Flow:
$0.00
Annual Cash Flow:
$0.00
Expense Breakdown (Monthly)
- Vacancy Loss: $0.00
- Property Mgmt: $0.00
- Repairs & CapEx: $0.00
- Taxes, Ins, HOA: $0.00
- Mortgage (P&I): $0.00
Net Operating Income (NOI):
$0.00
(Income minus operating expenses, before mortgage)
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function calculateRentalCashFlow() {
// Helper function to ensure valid number input
function getNum(id) {
var val = document.getElementById(id).value;
return parseFloat(val) || 0;
}
// 1. Income Inputs
var monthlyRent = getNum("monthlyRent");
var otherIncome = getNum("otherIncome");
// 2. Fixed Expense Inputs
var mortgagePayment = getNum("mortgagePayment");
var propertyTaxes = getNum("propertyTaxes");
var insurance = getNum("insurance");
var hoaFees = getNum("hoaFees");
// 3. Variable Expense Percentage Inputs
var vacancyRate = getNum("vacancyRate");
var repairsMaintenance = getNum("repairsMaintenance");
var capex = getNum("capex");
var managementFee = getNum("managementFee");
// — Calculations —
// Gross Income
var grossMonthlyIncome = monthlyRent + otherIncome;
// Calculate Variable Dollar Costs based on percentages of Gross Income
var vacancyCost = grossMonthlyIncome * (vacancyRate / 100);
var repairsCost = grossMonthlyIncome * (repairsMaintenance / 100);
var capexCost = grossMonthlyIncome * (capex / 100);
// Effective Gross Income (Income after vacancy loss)
var effectiveGrossIncome = grossMonthlyIncome – vacancyCost;
// Management fee is typically calculated on Effective Gross Income (collected rent)
var managementCost = effectiveGrossIncome * (managementFee / 100);
// Total Operating Expenses (Excluding Mortgage) for NOI calc
var totalFixedOperating = propertyTaxes + insurance + hoaFees;
var totalVariableOperating = repairsCost + capexCost + managementCost;
var totalOperatingExpensesNOI = totalFixedOperating + totalVariableOperating;
// Net Operating Income (NOI)
var netOperatingIncome = effectiveGrossIncome – totalOperatingExpensesNOI;
// Total Monthly Expenses (Operating Expenses + Mortgage P&I + Vacancy Loss)
// We add vacancy back here because it's a "cost" against gross income for cash flow purposes
var totalMonthlyExpenses = totalOperatingExpensesNOI + mortgagePayment + vacancyCost;
// Cash Flow Final Calc
var monthlyCashFlow = grossMonthlyIncome – totalMonthlyExpenses;
var annualCashFlow = monthlyCashFlow * 12;
// — Formatting and Display —
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
});
document.getElementById("resultGrossIncome").innerText = formatter.format(grossMonthlyIncome);
document.getElementById("resultTotalExpenses").innerText = formatter.format(totalMonthlyExpenses);
var monthlyCFEl = document.getElementById("resultMonthlyCashFlow");
monthlyCFEl.innerText = formatter.format(monthlyCashFlow);
if (monthlyCashFlow < 0) {
monthlyCFEl.parentElement.classList.add("negative");
monthlyCFEl.parentElement.style.color = "#dc3545";
} else {
monthlyCFEl.parentElement.classList.remove("negative");
monthlyCFEl.parentElement.style.color = "#28a745";
}
document.getElementById("resultAnnualCashFlow").innerText = formatter.format(annualCashFlow);
document.getElementById("resultNOI").innerText = formatter.format(netOperatingIncome);
// Update Breakdown
document.getElementById("summVacancy").innerText = formatter.format(vacancyCost);
document.getElementById("summMgmt").innerText = formatter.format(managementCost);
document.getElementById("summRepairsCapEx").innerText = formatter.format(repairsCost + capexCost);
document.getElementById("summFixed").innerText = formatter.format(totalFixedOperating);
document.getElementById("summMortgage").innerText = formatter.format(mortgagePayment);
document.getElementById("resultArea").style.display = "block";
}
Understanding Rental Property Cash Flow
Cash flow is the lifeblood of any rental property investment. It is the net amount of cash moving into or out of an investment after all operating expenses and debt service (mortgage payments) have been paid. Positive cash flow means the property is generating income for you every month, while negative cash flow means you are paying out of pocket to keep the property running.
While property appreciation is a long-term goal for many investors, real estate cash flow is what allows you to sustain the investment today. A property with strong positive cash flow is often referred to as a "cash cow," providing passive income and a buffer against market downturns. Conversely, a property with negative cash flow is sometimes called an "alligator" because it constantly eats up your capital.
The Critical Components of the Calculation
To accurately calculate cash flow, you must move beyond simple "Rent minus Mortgage." You need to account for all costs associated with owning and operating the asset.
- Gross Income: This is the total potential income from the property, including monthly rent and any ancillary income streams like parking fees, laundry machines, or storage rentals.
- Fixed Expenses: These are recurring, predictable monthly costs. They include your mortgage principal and interest (P&I), property taxes, landlord insurance policies, and HOA fees if applicable.
- Variable Expenses and Reserves (The "Hidden" Costs): These are often underestimated by novice investors. They include:
- Vacancy Rate: You will not collect rent 100% of the time. A 5% vacancy rate assumes the property sits empty for about 18 days per year depending on turnover.
- Repairs & Maintenance: Routine costs like fixing leaky faucets, painting between tenants, or lawn care.
- Capital Expenditures (CapEx): Setting aside money monthly for major future replacements like a new roof, HVAC system, or water heater.
- Property Management: Even if you manage it yourself, you should account for your time. Professional managers typically charge between 7% and 10% of collected rent.
Interpreting Your Results
This calculator provides several key metrics. Monthly Cash Flow is your actual "take-home" amount before income taxes. Net Operating Income (NOI) is a measure of the property's profitability before financing costs (mortgage) are considered, which is crucial for determining the asset's raw value independent of how it's leveraged.
If your cash flow is negative, you need to evaluate if the potential for high future appreciation justifies the monthly out-of-pocket cost, or if you need to increase rent or reduce expenses to make the deal viable.