Rental Property Cash Flow: The Only Number That Matters

Ask a new real estate investor why they're buying a rental property and you'll usually hear something about appreciation. "Property values always go up." "I'll build equity over time." "It's a long-term wealth play."

Sure. But appreciation is a guess about the future. Cash flow is money in your account this month. One of those things pays your bills. The other one looks good on a spreadsheet.

A Property That Looks Great on Paper

Let's walk through a real example. Here's a duplex listed at $280,000 in a mid-sized city. Each unit rents for $1,200/month. Gross rental income: $2,400/month, or $28,800/year.

You put 25% down ($70,000), which is the typical minimum for conventional multi-unit investment property loans, and finance the rest at 7.25% on a 30-year loan. Your monthly mortgage payment (principal and interest) is $1,432.

$2,400 rent minus $1,432 mortgage = $968/month. Almost a thousand bucks a month in cash flow, right?

Not even close.

Where the Money Actually Goes

Here's what that $2,400/month really looks like once you account for actual operating costs:

Property taxes: $375/month. This varies wildly by location, and it often increases after a property changes hands. Consider looking beyond the seller's tax bill – check what the assessment will reset to after purchase.

Insurance: $165/month (a reasonable estimate, though costs vary significantly by location and coverage). Landlord policies cost more than homeowner policies. If the property is in a flood zone, add more.

Vacancy: $192/month (8% of gross rent). You won't have both units rented every day of every year. Turnovers happen. Sometimes a unit sits empty for a month between tenants. Most investors budget 5-10% for vacancy; 8% accounts for roughly one month of vacancy per unit every two years.

Maintenance: $240/month (10% of gross rent). Industry rules of thumb typically suggest budgeting 8-12% of gross rent for maintenance. Two units means two sets of everything that can break. Water heaters, garbage disposals, faucets, doors, locks. Stuff breaks constantly.

CapEx reserves: $192/month (8% of gross rent, a commonly recommended reserve target). The roof will need replacing eventually. So will the furnace, the water heaters, the windows. Setting money aside monthly means a $12,000 roof replacement in year 9 doesn't come out of your pocket all at once.

Property management: $240/month (10% of gross rent, which falls within the typical 8-12% range charged by most property management companies). Even if you plan to self-manage, price this in. Your time has a cost. And if you ever want to step away from day-to-day management, you need the numbers to work with a manager in place.

Now let's add it up:

$2,400 rent – $2,836 expenses = –$436/month

That duplex doesn't cash flow. It bleeds $436 every month. You'd be writing a check to own this property.

How Did $968 Turn Into Negative $436?

Because most investors skip five line items. They calculate rent minus mortgage and call it a day. The real expenses – vacancy, maintenance, CapEx, and management – eat up $864/month that simply didn't exist in the napkin math.

This is exactly how people end up as "accidental landlords" who hate real estate investing. They bought based on the top-line number, and the real costs slowly drained them.

What a Cash-Flowing Property Looks Like

For this duplex to break even, rents would need to be roughly $2,850/month total – about $1,425 per unit. To cash flow $200/month (a modest positive), you'd need rents around $3,050/month.

Alternatively, if you could buy the same property for $220,000 instead of $280,000, your mortgage drops to $1,022/month and total expenses fall to around $2,426. Now you'd cash flow about –$26/month. Still not great, but much closer.

The point isn't that it takes magical deals. It's that running the real numbers and knowing exactly where the break-even line is for any property makes or breaks the investment.

The Metrics to Watch

Once you've calculated true cash flow, look at two additional numbers:

Cap rate. Take your annual net operating income (rent minus operating expenses, not including the mortgage) and divide by the purchase price. For this duplex: ($28,800 – $14,448) / $280,000 = 5.1%. That tells you the property's return regardless of financing. Useful for comparing deals.

Cash-on-cash return. Take your annual cash flow and divide by the total cash you invested (down payment + closing costs). If cash flow is negative, this number is negative too – a clear red flag.

Both metrics give you different angles on the same question: is this property actually making you money?

Stop Guessing

The difference between a good rental and a money pit is often $200-400/month in expenses that investors forget to include. It's worth avoiding that trap.

Run your numbers through the [rental property calculator](/calculators/rental-property) and see the real cash flow – every expense included, no surprises.

Sources

• LendingTree – Down Payment for Rental Property
• BiggerPockets – Investor Benchmarks for Vacancy, Maintenance, and PM
• Mynd Property Management – Average and Hidden Maintenance Costs for a Rental Property
• Benzinga – Real Estate CapEx Calculator
• Baselane – How Much Do Property Managers Charge?

---

*This article is for informational purposes only and does not constitute financial, legal, or tax advice. Consult a qualified professional for advice specific to your situation.*

FAQ

How do you calculate cash flow on a rental property?

Take your gross monthly rent and subtract all expenses: mortgage payment, property taxes, insurance, vacancy allowance (5-10%), maintenance (8-12% of rent), capital expenditure reserves (8%), and property management (8-12%). The number left is your true cash flow. Most investors who only subtract the mortgage payment are missing $800 or more per month in real costs.

What is a good cash-on-cash return for a rental property?

Most experienced investors target a cash-on-cash return of 8-12% in the current market. Calculate it by dividing your annual net cash flow by the total cash you invested (down payment plus closing costs). If this number is negative, the property is costing you money every month regardless of potential appreciation.

How much should I budget for rental property maintenance?

Budget 8-12% of gross monthly rent for routine maintenance, plus an additional 8% for capital expenditure reserves (roof, HVAC, water heaters, and other big-ticket items). On a property renting for $1,200 per month, that is roughly $200-$240 per month for maintenance and another $96 for CapEx. These costs are unavoidable over time, and skipping the budget just means bigger surprises later.

Should I include property management fees even if I self-manage?

Yes. Your time has a dollar value, and pricing in management at 8-12% of gross rent ensures the property cash flows on its own merits. If you ever want to step back from day-to-day management, buy another property, or sell, the numbers need to work with a manager in place. Self-managing is a bonus, not a requirement baked into the deal.

What is a good cap rate for a rental property?

Cap rate varies by market and property type, but most investors look for 5-8% in a typical metro area. Calculate it by dividing your annual net operating income (rent minus operating expenses, excluding the mortgage) by the purchase price. A higher cap rate means better returns relative to price, but also often comes with higher risk or less desirable locations.