Analyzing a rental comes down to one question: after every realistic expense and the mortgage payment, does the property make money — and is the return worth the cash you put in? Answering it requires keeping five numbers straight: net operating income (NOI), debt service, cash flow, cap rate, and cash-on-cash return.
The five numbers, defined
Net operating income (NOI)
NOI = effective rental income − operating expenses. Operating expenses include taxes, insurance, maintenance, management, reserves, and other costs of running the property. NOI excludes the mortgage — it measures the property, not the financing.
Debt service
Your loan payments: principal and interest. This is a financing cost, not an operating expense. Keeping it separate lets you compare properties regardless of how they're financed.
Cash flow
Cash flow = NOI − debt service. This is what's left for you each month or year.
Cap rate
Cap rate = annual NOI ÷ purchase price (or value). It describes the property's unleveraged return and is useful for comparing properties, but it ignores financing entirely.
Cash-on-cash return
Cash-on-cash = annual cash flow ÷ total cash invested (down payment, closing costs, upfront repairs, and reserves you set aside). It measures the return on your actual dollars.
Vacancy and reserve assumptions
Two assumptions separate realistic analysis from wishful thinking:
- Vacancy: no property is occupied 100% of the time. Turnover, marketing, and make-ready time cost rent. Investors commonly budget a percentage of gross rent; use local data and your own experience to choose it.
- Maintenance: routine repairs — leaky faucets, appliance service, landscaping.
- Capital expenditures (CapEx) reserves: money set aside for big-ticket replacements like roofs, HVAC systems, and water heaters. These don't happen monthly, but they do happen.
Skipping these makes nearly any property look profitable on paper.
Hypothetical example
Hypothetical rental — illustrative numbers only
- Purchase price
- $220,000
- Down payment (25%)
- $55,000
- Loan amount
- $165,000
- Sample rate / term (assumption, not a lender quote)
- 7% / 30 years
- Monthly principal & interest
- $1,097.75
- Gross rent
- $1,950/mo
- Vacancy (5%)
- −$97.50
- Effective income
- $1,852.50
- Maintenance 5% + CapEx 5% + management 8%
- −$351.00
- Taxes ($2,640/yr) + insurance ($1,200/yr)
- −$320.00
- NOI
- $1,181.50/mo ($14,178/yr)
- Cash flow ($1,181.50 − $1,097.75)
- $83.75/mo ($1,005/yr)
- Cap rate ($14,178 ÷ $220,000)
- 6.44%
- Cash invested ($55,000 down + $6,000 closing)
- $61,000
- Cash-on-cash ($1,005 ÷ $61,000)
- 1.65%
- Property-level DSCR ($1,181.50 ÷ $1,097.75)
- 1.08
All figures are made up for illustration. Maintenance, CapEx, and management are figured on gross rent. A solid-looking 6.44% cap rate produces a thin 1.65% cash-on-cash return once financing is added.
Reading the results
- Cap rate tells you how the property performs on its own. Compare it to similar properties in the same area.
- Cash flow tells you whether the property supports itself. Thin cash flow leaves little cushion for surprises.
- Cash-on-cash tells you what your invested cash earns. Compare it to your other options and your goals.
- Remember that cash flow isn't the only return — principal paydown, appreciation, and tax effects may matter too. Talk to a tax professional about your situation.
Common mistakes
- Counting the mortgage as an operating expense, which distorts NOI and cap rate.
- Assuming zero vacancy or no CapEx.
- Leaving out property management because you plan to self-manage — your time has value, and plans change.
- Using current taxes when a sale may trigger reassessment.
- Forgetting closing costs and upfront repairs in cash invested.
Next steps
Run your own deal in our Rental Property Calculator — it computes NOI, cash flow, cap rate, cash-on-cash, DSCR, and the maximum price that hits your target cash flow, all in your browser. Read our DSCR Loans guide to see how lenders may evaluate the same property differently. When you're ready, Financing Resources offers a referral to All Ways Capital LLC, which independently determines eligibility, terms, and approval.
Frequently asked questions
What's the difference between NOI and cash flow?
NOI is income minus operating expenses, before the mortgage. Cash flow is NOI minus debt service.
Is the mortgage an operating expense?
No. Principal and interest are financing costs (debt service), kept separate from operating expenses.
What is a good cap rate?
It depends on the market, property type, and risk. Compare against similar local properties rather than a universal target.
What is a good cash-on-cash return?
It depends on your goals and alternatives. The calculation helps you compare options consistently.
How much should I budget for vacancy and reserves?
Investors often use a percentage of rent for each. Use local rental data, the property's age, and your experience to choose realistic figures.
Why is my cash-on-cash much lower than my cap rate?
When debt payments consume most of the NOI, little cash flow remains relative to your invested cash. Financing terms strongly affect cash-on-cash.
Does the calculator save my numbers?
No. Our calculators run entirely in your browser; inputs are not sent or saved.
Run the numbers, then explore your options
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Educational content only — not legal, tax, financial, or lending advice. Examples are hypothetical and do not reflect actual rates, fees, or terms from any lender. Requirements and availability vary by lender and state; consult qualified professionals before making decisions.