Calculate your monthly Net Operating Income (NOI) and cash flow.
Income
Expenses & Debt Service
Variable Expenses (%)
Gross Monthly Income:$0.00
Total Monthly Expenses:$0.00
Net Operating Income (NOI):$0.00
Monthly Cash Flow:$0.00
Annual Cash Flow:$0.00
Understanding Rental Property Cash Flow
Calculating cash flow is the single most important step in evaluating a rental property investment. Cash flow represents the money remaining after all bills are paid. It is the "profit" you pocket every month.
How This Calculator Works
This tool takes into account both fixed and variable expenses to provide a realistic view of your potential returns:
Gross Income: The total of rent plus any additional income (laundry, parking, pet fees).
Vacancy Rate: Properties are rarely occupied 100% of the time. We deduct a percentage of rent (typically 5-8%) to account for turnover periods.
Operating Expenses: These include taxes, insurance, HOA fees, and property management costs.
Reserves (Repairs/CapEx): Smart investors set aside a percentage (often 10-15%) for future repairs and capital expenditures like a new roof or HVAC system.
Debt Service: The principal and interest portion of your mortgage payment.
Why is Positive Cash Flow Important?
Positive cash flow ensures that the property pays for itself. If you have negative cash flow, you are losing money every month to hold the asset. While appreciation is a bonus in real estate, cash flow is what keeps your business sustainable. A common benchmark for investors is the "1% Rule," which suggests the monthly rent should be at least 1% of the purchase price, though this varies by market.
The Formula
The calculation follows this standard formula:
Gross Income – Operating Expenses – Debt Service = Cash Flow
By accurately estimating expenses like vacancy and repairs upfront, you can avoid purchasing a liability disguised as an asset.
function calculateRentalCashFlow() {
// 1. Get Inputs
var monthlyRent = parseFloat(document.getElementById('rpMonthlyRent').value) || 0;
var otherIncome = parseFloat(document.getElementById('rpOtherIncome').value) || 0;
var mortgage = parseFloat(document.getElementById('rpMortgage').value) || 0;
var tax = parseFloat(document.getElementById('rpPropertyTax').value) || 0;
var insurance = parseFloat(document.getElementById('rpInsurance').value) || 0;
var hoa = parseFloat(document.getElementById('rpHOA').value) || 0;
var vacancyRate = parseFloat(document.getElementById('rpVacancyRate').value) || 0;
var repairRate = parseFloat(document.getElementById('rpRepairs').value) || 0;
var mgmtRate = parseFloat(document.getElementById('rpManagementFee').value) || 0;
// 2. Calculate Income
var grossPotentialIncome = monthlyRent + otherIncome;
// 3. Calculate Variable Expenses (based on Rent only, usually)
var vacancyCost = monthlyRent * (vacancyRate / 100);
var repairCost = monthlyRent * (repairRate / 100);
var mgmtCost = monthlyRent * (mgmtRate / 100);
// 4. Calculate Total Expenses
var totalFixedExpenses = tax + insurance + hoa;
var totalVariableExpenses = vacancyCost + repairCost + mgmtCost;
var totalOperatingExpenses = totalFixedExpenses + totalVariableExpenses;
// 5. Calculate Metrics
var effectiveGrossIncome = grossPotentialIncome – vacancyCost; // True income after vacancy
// Note: For simplicity in display, we group vacancy as an expense deduct or income loss.
// Standard Accounting: Gross Potential Rent – Vacancy = Effective Gross Income.
// Then EGI – Operating Expenses = NOI.
// Let's stick to the visual summary: Gross Income (Potential) vs Expenses
var totalExpensesDisplay = totalOperatingExpenses + mortgage; // Cash out
// Net Operating Income (NOI) = Income – Operating Expenses (Excluding Mortgage)
// Usually NOI uses Effective Gross Income.
var noi = (grossPotentialIncome – vacancyCost) – (totalOperatingExpenses – vacancyCost);
// Simplified: NOI = (Rent + Other) – (Vacancy + Taxes + Ins + HOA + Repairs + Mgmt)
var calculatedNOI = grossPotentialIncome – vacancyCost – repairCost – mgmtCost – tax – insurance – hoa;
var monthlyCashFlow = calculatedNOI – mortgage;
var annualCashFlow = monthlyCashFlow * 12;
// 6. Display Results
var resultDiv = document.getElementById('rpResults');
resultDiv.style.display = 'block';
document.getElementById('resGrossIncome').innerText = '$' + grossPotentialIncome.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
// Total cash out (Expenses + Mortgage)
var totalCashOut = totalOperatingExpenses + mortgage;
document.getElementById('resTotalExpenses').innerText = '$' + totalCashOut.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resNOI').innerText = '$' + calculatedNOI.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
var cfElement = document.getElementById('resMonthlyCashFlow');
cfElement.innerText = '$' + monthlyCashFlow.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
var acfElement = document.getElementById('resAnnualCashFlow');
acfElement.innerText = '$' + annualCashFlow.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
// Styling for negative numbers
if (monthlyCashFlow < 0) {
cfElement.classList.add('rp-negative');
acfElement.classList.add('rp-negative');
} else {
cfElement.classList.remove('rp-negative');
acfElement.classList.remove('rp-negative');
}
}