How to Analyze a Rental Property: Cash Flow, Cap Rate, and Cash-on-Cash Return

The three numbers that describe every rental deal

Strip away the listing photos and the agent's pro forma, and any rental property reduces to three numbers: the monthly cash flow it throws off, the cap rate it earns on its price, and the cash-on-cash return it pays on the money you actually put in. The rental property calculator computes all three from six inputs — purchase price, down payment percentage, mortgage rate, loan term, expected monthly rent, and monthly operating expenses. This guide explains what each number means, how they interact, and where investors most often fool themselves.

The distinction that matters most is levered versus unlevered. Cap rate is the unlevered yield: what the property earns as a percentage of its price, as if you had bought it with cash. It describes the property. Cash-on-cash return is the levered yield: what lands in your pocket after the mortgage, divided by your down payment. It describes your deal. Two investors buying identical houses at identical prices can see wildly different cash-on-cash returns purely because one locked a 5% rate and the other is paying 7%. Keeping the two metrics separate is the discipline that makes rental analysis honest.

How the numbers are calculated

The calculator runs five steps, and each one is simple arithmetic. The definitions are where the rigor lives.

Down payment        = Purchase price × Down payment %
Loan amount         = Purchase price − Down payment
Monthly payment     = L × r / (1 − (1 + r)^−n)
(r = annual rate / 12, n = years × 12)
NOI (annual)        = (Monthly rent − Monthly expenses) × 12
Cap rate            = NOI / Purchase price × 100
Annual cash flow    = NOI − 12 × Monthly payment
Cash-on-cash return = Annual cash flow / Down payment × 100

Net operating income is the pivot of the whole calculation, and it has a strict definition: rent minus operating expenses. Operating expenses include property taxes, landlord insurance, repairs and maintenance, property management, HOA dues, owner-paid utilities, and an allowance for vacancy. They exclude the mortgage entirely. That is not an oversight — it is what keeps cap rate comparable across buyers. Financing belongs to you; the expense ratio belongs to the property. The mortgage enters one line later, as debt service subtracted from NOI to produce cash flow. (For a deeper treatment of NOI and what counts as an operating expense, see the guide to how cap rate works.)

One invariant worth knowing: if you set the down payment to 100%, the loan disappears and cash-on-cash return collapses to exactly the cap rate. Leverage is the only thing separating the two numbers, which is why comparing them tells you — at a glance — whether your financing is helping or hurting.

Worked example: a $250,000 single-family rental

Take a tidy three-bedroom house in a Midwest metro listed at $250,000. You put 25% down — $62,500 — which is what conventional lenders commonly want for the best pricing on an investment property, leaving a $187,500 loan. You lock a 30-year mortgage at 6.5%, roughly where Freddie Mac's weekly survey has had 30-year money for much of the past year. Market rent is $2,200 a month. Your operating budget — property tax, insurance, a 1%-of-value maintenance reserve, a vacancy allowance, and self-management — comes to $850 a month.

Run those six numbers through the rental property calculator and here is what comes back:

Monthly mortgage payment   $1,185
NOI                        ($2,200 − $850) × 12 = $16,200
Cap rate                   $16,200 / $250,000 = 6.48%
Annual debt service        $1,185 × 12 = $14,221
Annual cash flow           $16,200 − $14,221 = $1,979 (≈ $165/mo)
Cash-on-cash return        $1,979 / $62,500 = 3.17%

Read the story in the gap between 6.48% and 3.17%. The property itself earns a respectable unlevered yield, but the 6.5% mortgage rate sits above the 6.48% cap rate — leverage is working slightly against you, dragging the levered return below the unlevered one. Now rerun the same deal at the 5% rates of a few years ago: the payment drops to about $1,007, annual cash flow jumps to roughly $4,120, and cash-on-cash return more than doubles to 6.6%. Same house, same rent, same expenses — the financing alone swings the return from mediocre to solid. That sensitivity is the single most important thing the calculator teaches, and it is why serious investors rerun the numbers every time rates move.

Factors that move the result

The mortgage rate versus the cap rate

This is the leverage rule, and it governs everything. When your borrowing rate is below the cap rate, every borrowed dollar earns more than it costs, and cash-on-cash return rises above the cap rate — positive leverage. When the borrowing rate is above the cap rate, as in the example, each borrowed dollar costs more than it earns and leverage becomes a drag. With 30-year rates in the mid-6s and typical single-family cap rates between 5% and 7%, many 2026 deals sit right at the crossover, which is why thin or negative cash flow is so common right now.

Operating expenses — the number people lowball

The single most common analysis error is an expense figure that only includes taxes and insurance. A durable budget also carries maintenance (a common rule of thumb is 1% of the property value per year, more for older homes), capital reserves for the roof and HVAC that will eventually fail, property management at 8–12% of rent if you ever outsource, and any HOA dues. Across a full hold period, total operating expenses on single-family rentals tend to land near 35–45% of rent — far above the number most first-time landlords pencil in.

Vacancy

No property collects rent 12 months a year forever. The US rental vacancy rate has run in the 6–7% range in recent years (the Census Bureau publishes it quarterly in its Housing Vacancies and Homeownership survey), and a single month of turnover on an annual lease is 8.3% vacancy by itself. Budgeting 5–8% of rent as a vacancy allowance inside your monthly expense figure keeps one bad turnover from wrecking a year.

Down payment size

A bigger down payment lowers the mortgage payment and raises cash flow, but it also raises the denominator of cash-on-cash return — so the percentage can fall even as the dollars improve. Whether more equity helps or hurts the return depends entirely on which side of the leverage rule the deal sits. Try 15%, 20%, and 25% in the calculator and watch both the monthly cash flow and the percentage; the down payment calculator will translate the percentages into the cash you need at closing.

Property taxes and insurance drift

Taxes get reassessed — often upward, and often triggered by your own purchase. Landlord insurance premiums have climbed sharply in storm- and wildfire-exposed states. Both live inside your expense number, and both drift upward faster than many leases allow rent to follow. Underwriting with this year's tax bill on last year's assessment is a quiet way to overstate NOI.

How to improve a marginal deal

• Buy the rate down or shop harder for financing. The worked example showed a 1.5-point rate difference doubling the return. Points, credit-union pricing, or a 25%-down tier can each move the rate more than any expense trim.
• Attack the biggest expense line, not the smallest. Appealing a property-tax assessment or re-shopping insurance moves hundreds a year; switching light bulbs does not.
• Raise effective rent, not just headline rent. Reducing turnover — the dominant real-world vacancy cost — through longer leases and responsive maintenance often adds more than a rent increase that drives a good tenant out.
• Consider house hacking. Owner-occupying one unit of a 2–4 unit building qualifies you for owner-occupant financing with lower rates and smaller down payments, transforming the cash-on-cash math.
• Walk away. The cheapest fix for a deal that only works at fantasy numbers is not buying it. The calculator is at its most valuable when the answer is no.

Common mistakes

Counting the mortgage as an operating expense. Folding debt service into the expense line corrupts both metrics at once: cap rate stops being comparable to market benchmarks, and the mortgage gets double-counted in cash flow. Keep expenses operating-only and let the calculator handle the debt separately.

Analyzing with zero vacancy and zero maintenance. A pro forma that assumes a tenant who never leaves and a house that never breaks will make almost anything look like a buy. If the deal only works at 100% occupancy, it does not work.

Confusing cash-on-cash return with total return. Cash-on-cash is deliberately narrow: pre-tax operating cash divided by cash in. It ignores principal paydown, appreciation, and tax effects such as the 27.5-year depreciation deduction on residential rentals (see IRS Publication 527). Those can add several points of annual return — but they arrive later, on paper, or at sale. Treat cash-on-cash as the floor, and model the full multi-year picture with an IRR calculator when you want the ceiling.

Screening with the 1% rule and stopping there. The 1% rule (monthly rent ≥ 1% of price) is a filter for shortlisting, calibrated for a lower-rate era. It knows nothing about your taxes, insurance, or mortgage rate — the exact inputs that decide whether today's deals cash flow. Shortlist with the rule; underwrite with the real numbers.

When the calculator is not enough

The calculator answers the operating question — does this property pay you to own it — and deliberately stops there. It does not model your tax bracket, depreciation recapture at sale, 1031 exchanges, entity structuring, or local landlord-tenant law, and none of its output is investment advice. Before closing on a first rental, an hour each with a CPA who handles rental schedules and a local property manager who knows real vacancy and turnover costs for the neighborhood is cheap insurance against the two most expensive surprises: taxes and tenants.

Frequently asked questions

What counts as a good cash-on-cash return in 2026? With 30-year money in the mid-6s, most investors are underwriting to 6–10%, and settling nearer the bottom of that range in strong markets. Below roughly 4%, you are taking landlord risk for less than a treasury pays; above 10% usually means a cheaper market, heavier management, or more risk being priced in.

Should closing costs count as cash invested? Strictly, yes — the textbook definition of cash invested is down payment plus closing costs plus any up-front rehab. This calculator uses the down payment alone to stay to six clean inputs, which flatters the return slightly. For a purchase with heavy closing costs or rehab, mentally add them to the denominator, or fold them into a higher effective down payment.

What is the 50% rule? A screening heuristic that says operating expenses (excluding the mortgage) tend to consume about half of rent over a long hold. It looks pessimistic next to a first-year budget because it embeds the lumpy years — the roof, the eviction, the long vacancy. If your expense estimate is far below 50% of rent, be sure you know which real line items make your property the exception.

Is negative cash flow ever acceptable? Only as a deliberate, funded bet on appreciation or rent growth — never as a surprise. Some investors in high-growth metros knowingly feed a property monthly. The failure mode is discovering the negative cash flow after closing because vacancy and maintenance were left out of the analysis.

Why is my cash-on-cash return below the cap rate? Your mortgage rate is above the cap rate, so leverage is subtracting rather than adding — each borrowed dollar costs more than it earns. Common at current rates. The gap closes as you shrink the loan and disappears entirely at 100% down, where the two metrics are equal by construction.

Does the calculator work outside the US? The math — amortization, NOI, cap rate, cash-on-cash — is universal; only the framing (down-payment norms, tax references) is US-specific. Enter your own currency's amounts and the percentages read the same anywhere.

Related calculators

The rental property calculator is the levered view of a deal; pair it with the cap rate calculator for the unlevered yield with vacancy modeled explicitly, the mortgage repayment calculator to see total interest over the life of the loan, the down payment calculator for the cash needed at closing, the rent vs buy calculator for the owner-occupier version of the question, and the ROI calculator (explained in depth in its own guide) for any investment beyond real estate.