Rental analysis
Rental Cash Flow Calculator
The full pro-forma from the rent check to the cash in your pocket: gross income, less a vacancy allowance, less operating expenses — that's NOI — less the mortgage. What's left is cash flow, worked line by line so you can see exactly where the money goes.
$2,940/yr · NOI $15,540/yr
Informational only, not professional advice. This projects cash flow from your own estimates — it doesn't know your market's vacancy, your actual expenses, or your tax situation. Underwrite conservatively.
Methodology
Cash flow is the bottom of a standard rental pro-forma, built from the same NOI foundation lenders and appraisers use (Investopedia: Net operating income), then carried one step further through the mortgage. The calculation:
- Gross income = monthly rent + other income
- Effective gross income = gross income − vacancy allowance
- Net operating income = effective gross income − operating expenses
- Cash flow = NOI − debt service (the mortgage principal & interest)
- Monthly figures are annualized by ×12
The line between NOI and cash flow is the mortgage: NOI describes the property regardless of how it's financed, while cash flow is what you personally keep after the loan. Keeping debt service separate is what lets the same NOI feed a cap rate (unlevered) and this cash-flow figure (levered) without double-counting.
Assumptions and limitations
- Operating expenses are entered as one monthly figure — itemize them in the NOI calculator if you want the breakdown.
- Debt service is principal & interest only; if taxes and insurance are escrowed into your payment, don't also count them in operating expenses.
- Pre-tax cash flow — depreciation, deductions, and your tax rate all change what you actually keep.
- Every input is your estimate; a light vacancy or maintenance number flows straight to an overstated result.
Built & reviewed by Eric, Founder against the cited primary sources shown in the methodology above. Last reviewed July 2026.
Frequently asked questions
What counts as cash flow on a rental property?
Cash flow is what's left after the property has paid for itself: gross rent and any other income, minus a vacancy allowance, minus operating expenses, minus the mortgage. It's the money that actually reaches your bank account, and it's different from net operating income (NOI), which stops before the mortgage. A property can have healthy NOI and still be cash-flow negative if the loan payment is large — which is exactly why this tool carries the math all the way through debt service. Positive monthly cash flow is what lets a rental survive a repair, a vacancy, or a rate change without you feeding it out of pocket.
Why include a vacancy allowance if the unit is rented?
Because no rental stays occupied every month forever. Tenants move out, units sit empty between leases, and turnovers take time to clean and re-let. Budgeting 5–8% of gross rent for vacancy — the exact figure depends on your market and tenant quality — means a normal empty month doesn't turn a profitable property into a losing one on paper. Underwriting at 100% occupancy is the most common way new investors overstate cash flow. Treat vacancy as a real, recurring cost even in a hot rental market, and adjust the percentage to what your area actually experiences.
What should operating expenses include?
Everything it costs to run the property except the mortgage: property taxes, insurance, repairs and maintenance, property management, any owner-paid utilities, HOA dues, and a reserve for big-ticket capital items like a roof or furnace. The mortgage is deliberately separate — it's debt service, not an operating expense, which is the line that separates NOI from cash flow. A frequent mistake is leaving out maintenance and capital reserves because nothing broke this month; averaged over years, those costs are real, and ignoring them inflates cash flow until the day the water heater fails.
Is positive cash flow enough to call a deal good?
It's necessary but not sufficient. Positive cash flow keeps the property self-sustaining, but it doesn't tell you whether your money is working hard — a deal can cash flow $50 a month and still be a poor use of a large down payment. That's what cash-on-cash return measures: the annual cash flow against the cash you invested. Use this calculator to confirm the property pays for itself and to see the margin of safety, then run the cash-on-cash return to judge whether the return justifies the capital tied up.
Related tools
Itemize income and operating expenses line by line to get a property's net operating income — the number cap rates and appraisals are built on.
Open tool →Cash-on-Cash Return CalculatorAnnual pre-tax cash flow after the mortgage, as a percentage of the cash you actually invested — cap rate's levered counterpart.
Open tool →DSCR CalculatorDebt service coverage ratio — net operating income divided by debt service, the number rental and DSCR-loan lenders use to size a loan, with common thresholds shown.
Open tool →