How to Calculate Rental Property Cash Flow

Cash flow is the single most important number in rental property investing. It tells you whether a property puts money in your pocket each month or drains it. Before you buy an investment property, you need to know how to calculate cash flow accurately — not the back-of-napkin version, but the real number that accounts for all expenses, vacancies, and debt service.

Here's a complete walkthrough of the math behind rental property cash flow analysis, with formulas you can apply to any deal.

What Cash Flow Means for Rental Properties

Cash flow is simply the money left over after you collect rent and pay all expenses, including your mortgage. Positive cash flow means the property earns more than it costs to own. Negative cash flow means you're subsidizing the property out of pocket every month.

The formula is straightforward:

Cash Flow = Gross Rental Income - Operating Expenses - Debt Service

But the devil is in the details of what counts as operating expenses and how to estimate them realistically. That's where most new investors get tripped up.

Step 1: Calculate Net Operating Income (NOI)

NOI is the property's income after all operating expenses but before mortgage payments. It's the most universal metric in commercial and residential investment real estate because it separates the property's performance from how you finance it.

NOI = Gross Rental Income - Vacancy Allowance - Operating Expenses

Operating expenses include:

• Property taxes: Typically 0.5%-2.5% of property value annually, depending on the state
• Insurance: Landlord policies run $800-$2,000/year for single-family homes
• Maintenance and repairs: Budget 5-10% of gross rent, or $100-$200/month for a typical single-family rental
• Property management: 8-10% of gross rent if you hire a manager (even if self-managing, include this to value your time)
• Capital expenditures (CapEx): 5-10% of gross rent set aside for roofs, HVAC, appliances, and other big-ticket items
• Vacancy: Budget 5-8% of gross rent to cover turnover periods
• Utilities: Only if landlord-paid (water, trash, etc.)

A conservative rule of thumb: operating expenses typically run 40-50% of gross rental income. On a $2,000/month rental, expect $800-$1,000/month in total operating costs.

Step 2: Calculate Cap Rate

The capitalization rate (cap rate) measures a property's return independent of financing. It answers: "If I bought this property with all cash, what would my annual return be?"

Cap Rate = NOI / Purchase Price

For example, a property with $14,400 NOI purchased for $300,000 has a cap rate of 4.8%. Cap rates vary by market and property type. In 2026, typical residential cap rates range from 4-7% in most markets, with higher rates in lower-cost cities and lower rates in expensive coastal metros.

Cap rate is useful for comparing properties because it strips out financing. A 6% cap rate property is generating better income relative to its price than a 4% cap rate property, regardless of how each is financed.

Step 3: Calculate Cash-on-Cash Return

Cash-on-cash return measures the annual return on the actual cash you invested — your down payment plus closing costs. This is the metric that tells you how hard your money is working.

Cash-on-Cash Return = Annual Pre-Tax Cash Flow / Total Cash Invested

If you put $60,000 down on a property (plus $5,000 in closing costs) and it generates $4,800/year in cash flow, your cash-on-cash return is 7.4%. Many investors target 8-12% cash-on-cash returns, though in high-appreciation markets, investors sometimes accept lower cash flow in exchange for equity growth.

The 1% Rule: A Quick Screening Tool

The 1% rule is a fast back-of-napkin test: monthly rent should be at least 1% of the purchase price. A $300,000 property should rent for at least $3,000/month to pass the 1% test.

In practice, the 1% rule is hard to hit in expensive markets. Many investors in high-cost cities aim for 0.7-0.8% and rely on appreciation to make up the difference. In affordable markets (the Midwest, Southeast), 1% deals still exist, especially with off-market properties or value-add opportunities.

The 1% rule is a screening tool, not a decision tool. Always run full cash flow analysis before buying.

Worked Example: $300K Property

Let's run the complete analysis on a realistic deal:

• Purchase price: $300,000
• Down payment: 20% ($60,000)
• Closing costs: $5,000
• Total cash invested: $65,000
• Mortgage: $240,000 at 7.0%, 30-year fixed = $1,597/month
• Monthly rent: $2,000

Monthly operating expenses:

• Property tax: $375 (1.5% annually)
• Insurance: $125
• Maintenance: $150 (7.5% of rent)
• CapEx reserve: $100 (5% of rent)
• Vacancy: $100 (5% of rent)
• Property management: $160 (8% of rent)
• Total operating expenses: $1,010/month

NOI: $2,000 - $1,010 = $990/month ($11,880/year)

Cap Rate: $11,880 / $300,000 = 3.96%

Cash Flow: $990 - $1,597 (mortgage) = -$607/month

This property is cash-flow negative. At $2,000/month rent on a $300,000 purchase with 7% rates, the numbers don't work. You'd need rent closer to $2,600/month to break even, or a significantly lower purchase price. This is why the 1% rule exists as a quick filter — this property only meets 0.67%.

Now let's adjust: if you find the same property for $250,000 (a better deal) with $2,000/month rent:

• Mortgage on $200,000: $1,331/month
• Operating expenses: ~$960/month (slightly lower tax base)
• NOI: $1,040/month ($12,480/year)
• Cash flow: $1,040 - $1,331 = -$291/month — still negative, but getting closer

At today's interest rates, many single-family rentals require either below-market purchase prices, above-market rents, or larger down payments to achieve positive cash flow. This is the reality of 7% mortgage rates.

Key Takeaways

• NOI tells you property performance. It strips out financing to show what the property earns on its own.
• Cap rate compares deals. Use it to evaluate properties against each other and against alternative investments.
• Cash-on-cash return measures your return. It accounts for leverage and tells you what your actual invested dollars earn.
• The 1% rule is a filter, not a verdict. Use it to quickly screen deals, then run full analysis on anything that passes.
• Be conservative with expenses. New investors consistently underestimate vacancy, maintenance, and CapEx. Use 40-50% of gross rent as a realistic expense ratio.

Every successful rental property investor runs these numbers before making an offer. Use our rental property calculator to analyze any deal in seconds — plug in the purchase price, rent, and expenses, and see your cash flow, cap rate, and cash-on-cash return instantly.