Please enter valid numeric values for all required fields.
Gross Monthly Income:$0.00
Vacancy Loss:$0.00
Operating Expenses (excl. Mortgage):$0.00
Net Operating Income (NOI):$0.00
Total Mortgage Payment:$0.00
Monthly Cash Flow
$0.00
Annual Cash Flow
$0.00
Understanding Rental Property Cash Flow
Cash flow is the lifeblood of any rental property investment. It represents the net amount of money moving in or out of your business every month. Positive cash flow means your property generates more income than it costs to own and operate, providing you with passive income. Negative cash flow means you are paying out of pocket to keep the property running.
How to Calculate Rental Cash Flow
This calculator breaks down the calculation into three main categories:
Gross Income: The total money collected from rent and other sources (laundry, parking fees).
Operating Expenses: Costs associated with running the property, excluding debt service. This includes taxes, insurance, HOA fees, and variable costs like repairs and vacancy reserves.
Debt Service (Mortgage): The principal and interest payments made to the lender.
The formula used is: Cash Flow = Gross Income – (Operating Expenses + Mortgage Payment).
Why Variable Expenses Matter
Many novice investors make the mistake of only subtracting the mortgage, taxes, and insurance from the rent to determine profit. However, realistic cash flow analysis must account for:
Vacancy: Properties will not be occupied 365 days a year. A 5-8% vacancy rate is a standard conservative estimate.
Repairs & Maintenance: To handle routine fixes (leaky faucets, painting).
CapEx (Capital Expenditures): Saving for big-ticket items like a new roof or HVAC system.
Using this calculator ensures you aren't blindsided by these inevitable costs, helping you make smarter investment decisions.
function calculateCashFlow() {
// Clear error
document.getElementById('error-message').style.display = 'none';
document.getElementById('results-area').style.display = 'none';
// Get Inputs
var monthlyRent = parseFloat(document.getElementById('monthlyRent').value);
var otherIncome = parseFloat(document.getElementById('otherIncome').value);
var mortgage = parseFloat(document.getElementById('mortgage').value);
var taxes = parseFloat(document.getElementById('taxes').value);
var insurance = parseFloat(document.getElementById('insurance').value);
var hoa = parseFloat(document.getElementById('hoa').value);
var vacancyRate = parseFloat(document.getElementById('vacancyRate').value);
var repairsRate = parseFloat(document.getElementById('repairsRate').value);
var capexRate = parseFloat(document.getElementById('capexRate').value);
var mgmtRate = parseFloat(document.getElementById('mgmtRate').value);
// Validation – Basic checks (IsNaN)
// Note: We allow 0 for many fields, but Rent usually shouldn't be NaN if user wants a result.
// We will treat empty/NaN non-required fields as 0 for smoother UX, but require Rent and Mortgage/Exp basics.
if (isNaN(monthlyRent)) monthlyRent = 0;
if (isNaN(otherIncome)) otherIncome = 0;
if (isNaN(mortgage)) mortgage = 0;
if (isNaN(taxes)) taxes = 0;
if (isNaN(insurance)) insurance = 0;
if (isNaN(hoa)) hoa = 0;
if (isNaN(vacancyRate)) vacancyRate = 0;
if (isNaN(repairsRate)) repairsRate = 0;
if (isNaN(capexRate)) capexRate = 0;
if (isNaN(mgmtRate)) mgmtRate = 0;
if (monthlyRent === 0 && mortgage === 0) {
document.getElementById('error-message').style.display = 'block';
return;
}
// Calculations
var grossIncome = monthlyRent + otherIncome;
// Calculate Variable Costs based on Gross Income
var vacancyCost = grossIncome * (vacancyRate / 100);
var repairsCost = grossIncome * (repairsRate / 100);
var capexCost = grossIncome * (capexRate / 100);
var mgmtCost = grossIncome * (mgmtRate / 100);
var totalVariableExpenses = repairsCost + capexCost + mgmtCost; // Vacancy is usually deducted from Gross to get Effective Gross, but functionally it's an expense/loss.
// Standard definition: Effective Gross Income = Gross – Vacancy.
// Expenses deducted from Effective Gross.
var effectiveGrossIncome = grossIncome – vacancyCost;
var totalFixedExpenses = taxes + insurance + hoa;
var totalOperatingExpenses = totalFixedExpenses + totalVariableExpenses;
var noi = effectiveGrossIncome – totalOperatingExpenses;
var monthlyCashFlow = noi – mortgage;
var annualCashFlow = monthlyCashFlow * 12;
// Display Results
var currencyFormatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
});
document.getElementById('res-gross-income').innerText = currencyFormatter.format(grossIncome);
document.getElementById('res-vacancy').innerText = "-" + currencyFormatter.format(vacancyCost);
document.getElementById('res-operating-exp').innerText = "-" + currencyFormatter.format(totalOperatingExpenses);
document.getElementById('res-noi').innerText = currencyFormatter.format(noi);
document.getElementById('res-mortgage').innerText = "-" + currencyFormatter.format(mortgage);
var cfElement = document.getElementById('res-cashflow');
var annualCfElement = document.getElementById('res-annual-cashflow');
cfElement.innerText = currencyFormatter.format(monthlyCashFlow);
annualCfElement.innerText = currencyFormatter.format(annualCashFlow);
// Styling based on positive/negative
if (monthlyCashFlow >= 0) {
cfElement.className = "positive-flow";
annualCfElement.className = "positive-flow";
} else {
cfElement.className = "negative-flow";
annualCfElement.className = "negative-flow";
}
document.getElementById('results-area').style.display = 'block';
}