How to Calculate Rental Property Cash Flow (2026 Guide)

Learning how to calculate rental property cash flow is the difference between building wealth and quietly losing money every month. Most new investors run a napkin math check — rent minus mortgage — and call it a day. Then reality shows up in the form of a busted water heater, a two-month vacancy, or a property tax reassessment.

This guide walks you through the exact formula seasoned landlords use, the expense line items rookies forget, and the benchmarks that separate a real deal from a money pit. By the end, you’ll be able to analyze any property in under ten minutes.

What Cash Flow Actually Means (And What It Doesn’t)

Cash flow is simple in concept: it’s the money left in your bank account at the end of the month after the property has paid all of its own bills. Positive cash flow means the tenant is paying you to own the house. Negative cash flow means you’re paying them.

Here’s what cash flow is not:

• It’s not appreciation. That’s a paper gain you can’t spend.
• It’s not principal paydown. That’s equity building — great, but not cash.
• It’s not tax deductions. Depreciation looks good on paper but doesn’t buy groceries.

Cash flow is the boring, honest number that determines whether you can keep the property when the furnace dies in February. Everything else in real estate math is downstream of it.

How to Calculate Rental Property Cash Flow: The Formula

The core formula is stupid simple. Getting the inputs right is where 90% of investors go wrong.

Monthly Cash Flow = Gross Rent − Operating Expenses − Debt Service

Let’s break down each piece so you can plug in real numbers, not fantasy ones.

Step 1: Estimate Gross Rent (Realistically)

Don’t use the listing agent’s projected rent. Pull three data points:

1. Actual leases signed in the last 90 days within 0.5 miles (ask a local agent for comps).
2. Zillow Rent Estimate and Rentometer — take the lower of the two.
3. A quick Craigslist and Facebook Marketplace scan for identical bed/bath counts.

Use the lowest defensible number. If the deal only works at top-of-market rent, it doesn’t work.

Step 2: Subtract Vacancy and Bad Debt

Nobody rents a property 365 days a year forever. Even great tenants move out, and turnover eats 2–4 weeks between leases. Use a 5–8% vacancy allowance in stable markets and 10% in softer ones. Add another 1–2% for bad debt (tenants who stop paying and take months to evict).

Step 3: Add Up Operating Expenses

This is where deals die. Operating expenses typically run 35–50% of gross rent — the classic “50% rule” from real estate investing exists for a reason. Here’s the full list to price out.

• Property taxes — check the county assessor for the reassessed value after sale, not the current bill.
• Insurance — get an actual quote; rates have surged in coastal and wildfire states.
• Property management — 8–10% of collected rent, even if you self-manage (your time isn’t free).
• Repairs and maintenance — budget 5–10% of rent, higher on properties over 30 years old.
• Capital expenditures (CapEx) — 5–10% for the roof, HVAC, water heater, and appliances that will eventually die.
• Utilities — only what the landlord pays (often water, sewer, trash in multi-units).
• HOA fees — condos and some SFHs.
• Landscaping and snow removal — depends on climate and unit count.
• Leasing fees — 50–100% of one month’s rent every time you turn a tenant.

The IRS actually publishes a helpful primer on what counts as a deductible operating expense on rental property in Publication 527 — worth a skim before your first tax season.

Step 4: Subtract Debt Service (PITI + PMI if any)

Your mortgage principal and interest is only part of the monthly payment. Your lender likely escrows taxes and insurance, so make sure you don’t double-count those in expenses. A clean way: track the mortgage P&I only under debt service, and put taxes/insurance under operating expenses.

A Realistic Example: The $250,000 Duplex

Numbers speak louder than formulas. Here’s a side-by-side of the “rookie math” every listing tries to sell you, and the honest math a real investor runs.

Same property. Same rent. Same mortgage. A swing of roughly $900 a month — and the honest version is losing money before a single tenant turns over. This is why deals that “pencil out” on Zillow’s calculator so often bleed cash in real life.

The Cash-on-Cash Return Sanity Check

Cash flow in dollars is useful, but cash flow as a percentage of the money you put in is how you compare deals. That’s cash-on-cash return.

Cash-on-Cash Return = (Annual Cash Flow ÷ Total Cash Invested) × 100

“Total cash invested” means down payment + closing costs + rehab + any lease-up carrying costs. A common benchmark:

• Under 6% — usually too thin unless the appreciation story is strong.
• 6–10% — the middle band most experienced investors accept.
• Above 10% — either a great deal or a great story; verify carefully.

If you’d rather not build the model yourself, the Rental Property Analyzer spreadsheet plugs all of these lines into Google Sheets and Excel so you can price a deal in ten minutes flat. There’s also a free rental property calculator on our site if you just want to run a quick check without spinning up a spreadsheet.

Benchmarks: What Counts as “Good” Cash Flow?

The old rule of thumb was $100–$200 of cash flow per unit, per month, after all expenses and debt service. In 2026’s higher-rate environment, honest investors have adjusted:

• Single-family in stable markets: break-even to $150/month is common; profit comes from appreciation and paydown.
• Small multifamily (2–4 units): $150–$300 per unit is a healthy target.
• Value-add or BRRRR deals: aim for $200+ per unit after refinance, since your invested cash is lower.

Rents grew roughly 0.2% year-over-year in mid-2025 according to the Zillow rental research index, which is well below the historical average. That means underwriting for rent growth is riskier than it was in 2021 — assume flat rent for the first two years and you’ll rarely be disappointed.

The 5 Mistakes That Kill Rookie Deals

1. Zero CapEx reserve. A $12,000 roof over 20 years is $50/month whether you save for it or not.
2. Assuming self-management is free. Even if you manage the property, your time has a price. Budget the fee.
3. Using pre-sale property taxes. Most counties reassess on sale. Your bill will jump.
4. Ignoring insurance inflation. Landlord policies have gone up 20–40% in many states over the last three years.
5. Skipping the second walkthrough. A surprise sewer line or foundation crack can eat two years of cash flow in one repair.

Frequently Asked Questions

How much cash flow should a rental property make per month?

A commonly quoted target is $100–$200 per unit per month after all expenses, reserves, and debt service. In today’s rate environment, breaking even with strong appreciation potential is also acceptable, but negative cash flow should almost always be a hard no unless there’s a specific plan to raise rent or refinance.

What’s the 1% rule and does it still work?

The 1% rule says gross monthly rent should be at least 1% of the purchase price. It’s a screening shortcut, not underwriting. In 2026 most Sun Belt and Midwest markets have shifted closer to a 0.7–0.8% ratio, so use it to filter listings, then run the full cash flow formula on anything that passes.

Do I include mortgage principal in cash flow?

Yes — the entire monthly mortgage payment (principal + interest) is subtracted as debt service when you calculate cash flow. The principal portion is separately tracked as “equity build” or “principal paydown” if you want to measure your total return, but for cash-in-hand cash flow, the whole payment goes out.

How do I forecast cash flow before I buy?

Use market rent (not asking rent), the actual post-sale property tax bill, an insurance quote in writing, and reserves for vacancy, repairs, CapEx, and management — even if you plan to self-manage. Model it in a spreadsheet like the Landlord Rental Tracker so you can compare projected numbers to actuals once you own the property.

What if the numbers don’t work?

Walk. There will be another deal next week. The most expensive lesson in real estate is buying a bad property because you’re emotionally invested. Underwriting exists precisely so you can say no without regret.

Your Next Move

Now that you know how to calculate rental property cash flow, put it to work on the next three listings you scroll past. Run the honest math — vacancy, CapEx, management, real property taxes, real insurance — and see how many still look attractive. That filter alone will make you a better investor than most.

If you want a battle-tested spreadsheet that handles fix-and-flip, BRRRR, and long-term rentals in one file, the Real Estate Investor Toolkit bundles every calculator you’ll need. Analyze faster, buy smarter, sleep better.