Understanding cash flow is the cornerstone of successful real estate investing. This Rental Property Cash Flow Calculator helps investors determine the profitability of a rental unit by subtracting all operating expenses from the total income generated by the property.
Why is Cash Flow Important?
Positive cash flow means your property generates more income than it costs to own and operate. This surplus can be used to reinvest, save for future repairs, or provide passive income. Negative cash flow implies you must contribute money from your own pocket every month to keep the property, which increases investment risk.
Key Inputs Explained
Monthly Rent: The total amount you charge tenants per month.
Vacancy Rate: An estimate of the percentage of time the property will sit empty. A standard conservative estimate is 5-8%.
Mortgage (P&I): Your principal and interest payments to the lender.
Maintenance & CapEx: Money set aside for routine repairs (leaky faucets) and major capital expenditures (new roof, HVAC).
Management Fee: If you hire a property manager, they typically charge 8-10% of the collected rent.
How the Formula Works
The calculation follows a standard real estate formula:
Gross Income = (Monthly Rent + Other Income) * (1 – Vacancy Rate)
Total Expenses = Mortgage + Taxes + Insurance + HOA + Management Fees + Repairs + CapEx
Cash Flow = Gross Income – Total Expenses
Interpreting Your Results
If the calculator shows a positive number (Green), your property is generating profit. A generally accepted goal for a single-family rental is $100-$200 per door in pure cash flow per month. If the result is negative (Red), you should re-evaluate the deal, negotiate a lower price, or look for ways to increase rent or decrease expenses.
function calculateRentalCashFlow() {
// 1. Get Input Values
var monthlyRent = parseFloat(document.getElementById('rpMonthlyRent').value) || 0;
var otherIncome = parseFloat(document.getElementById('rpOtherIncome').value) || 0;
var vacancyRate = parseFloat(document.getElementById('rpVacancyRate').value) || 0;
var mortgage = parseFloat(document.getElementById('rpMortgage').value) || 0;
var annualTax = parseFloat(document.getElementById('rpPropertyTax').value) || 0;
var annualInsurance = parseFloat(document.getElementById('rpInsurance').value) || 0;
var repairsPercent = parseFloat(document.getElementById('rpRepairs').value) || 0;
var capexPercent = parseFloat(document.getElementById('rpCapEx').value) || 0;
var managementPercent = parseFloat(document.getElementById('rpManagement').value) || 0;
var hoa = parseFloat(document.getElementById('rpHOA').value) || 0;
// 2. Calculate Effective Gross Income
var potentialIncome = monthlyRent + otherIncome;
var vacancyLoss = potentialIncome * (vacancyRate / 100);
var effectiveGrossIncome = potentialIncome – vacancyLoss;
// 3. Calculate Monthly Expenses
var monthlyTax = annualTax / 12;
var monthlyInsurance = annualInsurance / 12;
var repairsCost = monthlyRent * (repairsPercent / 100);
var capexCost = monthlyRent * (capexPercent / 100);
var managementCost = monthlyRent * (managementPercent / 100); // Usually charged on collected rent, simplified to rent here
var totalMonthlyExpenses = mortgage + monthlyTax + monthlyInsurance + repairsCost + capexCost + managementCost + hoa;
// 4. Calculate Cash Flow & NOI
// NOI excludes debt service (mortgage) usually, but for cash flow we subtract everything.
// Let's calculate standard NOI first (Income – Operating Expenses). Mortgage is not an operating expense.
var operatingExpenses = monthlyTax + monthlyInsurance + repairsCost + capexCost + managementCost + hoa;
var monthlyNOI = effectiveGrossIncome – operatingExpenses;
var monthlyCashFlow = effectiveGrossIncome – totalMonthlyExpenses;
var annualCashFlow = monthlyCashFlow * 12;
// 5. Display Results
var resultDiv = document.getElementById('rpResults');
resultDiv.style.display = "block";
// Format Currency Helper
function formatMoney(num) {
return "$" + num.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
}
document.getElementById('resGrossIncome').innerText = formatMoney(effectiveGrossIncome);
document.getElementById('resTotalExpenses').innerText = formatMoney(totalMonthlyExpenses);
document.getElementById('resNOI').innerText = formatMoney(monthlyNOI);
var cfElement = document.getElementById('resCashFlow');
cfElement.innerText = formatMoney(monthlyCashFlow);
// Change color based on positive/negative flow
if (monthlyCashFlow >= 0) {
cfElement.className = "rp-result-value rp-highlight";
} else {
cfElement.className = "rp-result-value rp-highlight-neg";
}
var annualCfElement = document.getElementById('resAnnualCashFlow');
annualCfElement.innerText = formatMoney(annualCashFlow);
if (annualCashFlow >= 0) {
annualCfElement.className = "rp-result-value"; // standard color
} else {
annualCfElement.className = "rp-result-value rp-highlight-neg";
}
}