How to Calculate Rental Property Cash Flow — The Right Way

Cash flow is the first metric most real estate investors talk about and the first metric most of them calculate wrong. Overestimated cash flow is the most common reason investors buy properties that perform poorly — the numbers looked great on paper but collapsed in practice.

This guide shows you how to calculate cash flow correctly, what expenses most investors miss, and what benchmarks to use when evaluating deals.

The Cash Flow Formula

Cash flow is simple in concept:

Cash Flow = Rental Income – All Expenses

The complexity is in "all expenses." Most beginning investors dramatically undercount expenses, which produces inflated cash flow projections and bad investment decisions.

Step 1: Calculate Effective Gross Income

Start with gross potential rent — what the property could generate at full occupancy. Then apply a vacancy factor.

Gross Potential Rent: What the market will pay at 100% occupancy. If you have a two-unit building at $1,400/unit, gross potential rent is $2,800/month.

Vacancy: No property is occupied 100% of the time. Turnover creates gaps. Even in tight markets, assume 5% vacancy. In markets with more turnover or higher price points, assume 8-10%.

Effective Gross Income = Gross Potential Rent × (1 – Vacancy Rate)

On $2,800/month at 5% vacancy: $2,800 × 0.95 = $2,660 effective gross income

Some investors also subtract a credit loss factor (1-2%) to account for non-paying tenants, evictions, and partial payments. For conservative underwriting, include it.

Step 2: Calculate Operating Expenses

This is where most investors undercount. Operating expenses for a rental property include:

Property Taxes

Look up the actual assessed property tax, not just the current owner's payment. Property taxes often reset (higher) on sale. In many states, reassessment happens at sale — verify the post-purchase tax amount with your local assessor's office.

Insurance

Landlord insurance (also called dwelling fire or rental property insurance) is different from homeowner's insurance and typically costs 15-25% more. For a single-family rental worth $350,000, budget $1,500 – $2,500/year.

Property Management

If you hire a property manager (and you should, unless managing is your plan), budget 8-12% of gross collected rents. On $2,660/month, that is $213 – $319/month, or $2,555 – $3,830/year.

Critical note: Even if you self-manage, your time has real value. If you spend 5 hours/month managing a property and your time is worth $50/hour, that is $250/month in implied cost. Conservative underwriting includes management fees regardless of your intention.

Maintenance and Repairs

The standard rule is 1% of property value per year for maintenance. On a $350,000 property: $3,500/year, or $292/month.

This is an average across time — some years you spend nothing, some years you spend $8,000 replacing the water heater and fixing a broken sewer line. The average holds over time.

Older properties (pre-1980) often require 1.5-2% of value per year. Factor this in when underwriting older homes.

Capital Expenditures (CapEx)

CapEx is the big one that new investors almost always omit. CapEx refers to major replacement costs: roof, HVAC, water heater, appliances, flooring, windows, exterior paint.

Standard reserve: 1-2% of property value per year. On a $350,000 property: $3,500 – $7,000/year.

If the property is newly renovated with new systems, you can be at the lower end. If the roof is 18 years old and the HVAC is 15 years old, be at the higher end.

Never skip CapEx reserves. Investors who exclude them are not generating higher cash flow — they are generating cash flow that will be wiped out the first time something major breaks.

HOA Fees

If applicable. These are non-negotiable and can be significant ($200-$500+/month in some markets). Always verify HOA fee amounts and whether special assessments are pending.

Lawn, Snow, and Utilities

If any utilities are owner-paid, include them. If lawn care or snow removal is your responsibility, include those costs.

Step 3: Calculate Net Operating Income (NOI)

NOI = Effective Gross Income – Operating Expenses

Using our $350,000 single-family example at $1,800/month rent:

Item	Annual Amount
Gross rent	$21,600
Less vacancy (5%)	($1,080)
Effective gross income	$20,520
Less property taxes	($5,000)
Less insurance	($2,000)
Less property management (10%)	($2,052)
Less maintenance (1%)	($3,500)
Less CapEx reserve (1%)	($3,500)
NOI	$4,468

NOI is a pre-debt metric. It tells you what the property generates before your mortgage.

Step 4: Calculate Cash Flow After Debt Service

If you financed the property, subtract your annual mortgage payment (principal + interest):

Cash Flow = NOI – Annual Debt Service

On a $350,000 property purchased with 25% down ($87,500) and a $262,500 mortgage at 7.5% for 30 years:

Monthly P&I: approximately $1,836/month = $22,032/year

Annual Cash Flow = $4,468 NOI – $22,032 debt service = -$17,564

This property does not cash flow at these numbers. This is a very common outcome in most major markets — properties at market-rate prices in high-rate environments often produce negative cash flow with conventional financing.

This does not necessarily make the property a bad investment. Appreciation, debt paydown, and tax benefits may still produce attractive total returns. But you need to know the real cash flow before you buy.

The Metrics That Matter

Cash-on-Cash Return (CoC)

CoC = Annual Cash Flow ÷ Total Cash Invested

If you invested $100,000 in down payment and closing costs and the property produces $6,000/year in cash flow: $6,000 ÷ $100,000 = 6% CoC

Target CoC return: 8%+ is good in most markets; 6-7% is marginal; below 5% is difficult to justify unless you have very high conviction on appreciation.

Debt Service Coverage Ratio (DSCR)

DSCR = NOI ÷ Annual Debt Service

A DSCR above 1.0 means the property covers its debt from income. Below 1.0 means you are subsidizing the mortgage from other income.

Lenders typically require 1.2 DSCR minimum for investment property loans (meaning the NOI is 20% more than the debt service). In the example above, DSCR = $4,468 ÷ $22,032 = 0.20 — this property would not qualify for most investment property loans based on income alone.

What Good Cash Flow Looks Like

In the current rate environment (7-8% interest rates), most full-price market-rate residential properties do not cash flow positively with conventional financing. This is a mathematical reality, not a failure of underwriting.

Properties that cash flow today are typically:

Purchased at a significant discount to market (distressed, inherited, or under-valued)
In secondary and tertiary markets with lower purchase prices relative to rents
Multi-family (2-4 units) where combined income improves the math
Purchased with owner-occupant financing (lower rates, smaller down payment)
Value-add situations where below-market rents can be raised after acquisition

Knowing the real cash flow before you buy is the difference between an investment and a hope.

Running the Numbers Efficiently

Running full cash flow analysis on every property you look at is time-consuming — which is why most investors shortcut and get the numbers wrong.

Our Real Estate Investment Analyzer does all of this automatically. Enter the purchase price, rent estimate, and expense inputs, and it outputs NOI, cash flow, CoC return, cap rate, and DSCR instantly. It also runs a 10-year projection with adjustable appreciation and rent growth assumptions, so you can see total return, not just annual cash flow.