Real estate is one of the oldest ways to build wealth, and one of the easiest ways to lose money slowly. The difference is usually not luck or timing. It's whether someone ran the numbers honestly before buying.
This guide teaches the core skill under every rental decision: analyzing a property's income, expenses, and returns. It's step 1 of our Real Estate learning path and part of the Money & Investing path. It uses the same method as our data analysis guide: start with the decision, use real numbers, compare against a baseline, and stress-test the result. All you need is a spreadsheet.
Before you analyze: is a rental right for you?
Owning a rental is a small business, not a passive investment. Before running numbers on a property, check the basics:
- Your foundation is solid. You have an emergency fund, no high-interest debt, and stable income. Our budgeting and emergency fund guide covers this.
- You can absorb surprises. A furnace, a roof, or three months of vacancy can arrive in the same year.
- You understand the work, or the cost of paying someone to do it: tenant screening, leases, repairs, rent collection, and legal compliance.
- You've compared the alternatives. You can also own real estate through REITs (real estate investment trusts), which trade like stocks and must distribute most of their taxable income as dividends. Our stock market guide covers buying funds through a brokerage. REITs give up control and leverage, but need far less money, time, and risk tolerance.
The numbers that matter
| Metric | Formula | What it tells you |
|---|---|---|
| Gross scheduled rent | Monthly rent × 12 | Income if every unit is rented all year |
| Vacancy and credit loss | Gross rent × vacancy rate | Months empty, and rent you never collect |
| Effective gross income (EGI) | Gross rent − vacancy | Realistic income |
| Operating expenses | Taxes + insurance + maintenance + capital reserves + management + utilities + HOA + other | The cost of running the property (not the mortgage) |
| Net operating income (NOI) | EGI − operating expenses | What the property earns before financing |
| Cap rate | NOI ÷ purchase price | Return on the price as if bought with cash; used to compare properties |
| Debt service | Annual mortgage principal + interest | What your loan costs each year |
| Cash flow | NOI − debt service | What you actually keep (or pay) each year |
| Cash-on-cash return | Annual cash flow ÷ total cash invested | Return on the money you put in |
| DSCR | NOI ÷ debt service | Whether the property can carry its loan; lenders often look for at least 1.2 or more on investment loans |
Two rules of thumb you'll hear, and their limits:
- The 1% rule: monthly rent should be at least 1% of the purchase price. It's a quick screen, not an analysis, and it's hard to meet in many expensive markets.
- The 50% rule: operating expenses (excluding the mortgage) often run around half of rent over time. It's a sanity check on your expense estimates, not a substitute for them.
A worked example, line by line
Imagine a small single-family rental, or a duplex, listed at $250,000. It rents for $2,100 a month in total. You'd put 25% down with a 30-year fixed loan at 7%.
Step 1: Your cash invested
| Item | Amount |
|---|---|
| Down payment (25%) | $62,500 |
| Closing costs (estimate) | $7,500 |
| Initial repairs | $5,000 |
| Total cash invested | $75,000 |
| Loan amount | $187,500 |
Step 2: Income
| Item | Annual |
|---|---|
| Gross scheduled rent ($2,100 × 12) | $25,200 |
| Vacancy and credit loss (5%) | −$1,260 |
| Effective gross income | $23,940 |
Five percent vacancy is about 18 days a year. If your local market or tenant turnover suggests more, use more.
Step 3: Operating expenses
| Item | Basis | Annual |
|---|---|---|
| Property taxes | From the county assessor (check post-sale reassessment) | $3,000 |
| Landlord insurance | Quote from an insurer | $1,500 |
| Maintenance | 8% of gross rent | $2,016 |
| Capital expenditure reserves | 8% of gross rent (roof, HVAC, appliances, flooring) | $2,016 |
| Property management | 8% of collected rent | $1,915 |
| Total operating expenses | $10,447 |
Include management even if you'll self-manage. Your time has value, and the number tells you whether the deal still works if you ever hire someone.
Step 4: NOI and cap rate
- NOI = $23,940 − $10,447 = $13,493
- Cap rate = $13,493 ÷ $250,000 = 5.4%
Step 5: Financing and cash flow
- Monthly principal and interest on $187,500 at 7% for 30 years ≈ $1,247
- Annual debt service ≈ $14,969
- Annual cash flow = $13,493 − $14,969 = −$1,477, about −$123 a month
- Cash-on-cash return = −$1,477 ÷ $75,000 ≈ −2.0%
- DSCR = $13,493 ÷ $14,969 ≈ 0.90
- 1% rule check: $2,100 ÷ $250,000 = 0.84%, below the 1% screen
This property looks reasonable on the listing. Honest numbers show it loses money every month, can't cover its own loan, and would likely struggle to qualify for many investment loans.
Step 6: Stress-test and find what would make it work
| Scenario | Monthly cash flow | Cap rate | Takeaway |
|---|---|---|---|
| Base case: $2,100 rent, 7% rate | about −$123 | 5.4% | Loses money |
| Same property, 6% rate | about $0 | 5.4% | Breaks even; one repair puts it underwater |
| $2,400 rent, 7% rate | about +$91 | 6.4% | Positive, but thin |
| Base case plus a $6,000 roof repair in year one | about −$623 a month, averaged over that year | 5.4% | Why capital reserves matter |
Notice that the cap rate doesn't change with the interest rate, because it ignores financing. That's why you need both property metrics (NOI, cap rate) and deal metrics (cash flow, cash-on-cash, DSCR).
Owners also build equity as the loan is paid down (about $1,900 of principal in year one here) and may benefit from appreciation and tax deductions. Those are real, but they're not cash you can use to pay the mortgage, and appreciation isn't guaranteed. A deal that only works if prices rise is a bet, not an analysis.
Where to get honest numbers
| Number | Where to find it |
|---|---|
| Rent | Current leases and rent rolls from the seller; comparable rentals nearby; HUD Fair Market Rents as a reference point; local property managers |
| Property taxes | The county assessor's site; ask how taxes change after a sale, since many areas reassess at the new price |
| Insurance | A quote for a landlord (dwelling fire) policy, not a homeowner's policy |
| Repairs and capital needs | A professional inspection, plus the age of the roof, HVAC, water heater, plumbing, and electrical |
| Utilities and HOA | Seller's bills and HOA documents; check for special assessments |
| Mortgage terms | Written loan estimates from at least two or three lenders |
| Sale history and price estimates | County records; listing sites. Automated price estimates are a starting point, not an appraisal |
Treat the listing's "projected rent" and "estimated return" figures as marketing until you verify them. Our Claude + Zillow article covers how listing platforms and AI tools fit into this research, and where their estimates come from.
Financing basics
- Owner-occupied vs investment loans. If you'll live in the property, you may qualify for owner-occupied financing with a much smaller down payment. In the US, FHA loans can allow as little as 3.5% down on one-to-four-unit homes if you live in one unit and meet credit requirements. This is the idea behind "house hacking." Loans for pure investment properties usually require a larger down payment, often 15% to 25% or more, and may carry higher rates.
- Get loan estimates in writing and compare the APR, rate, points, and closing costs. The Consumer Financial Protection Bureau has free tools for comparing mortgage offers.
- Reserves: lenders often require several months of payments in reserve for investment properties. Even if yours doesn't, keep them.
Risks and rules beginners miss
- Concentration: one property is a large, illiquid bet on one location.
- Leverage cuts both ways: a loan magnifies gains and losses.
- Liquidity: selling takes months and costs a significant share of the price in commissions and closing costs.
- Fair housing: in the US, the federal Fair Housing Act prohibits discrimination in renting based on race, color, religion, sex, national origin, familial status, or disability. Many states and cities add more protected classes. Use written, consistent screening criteria for every applicant.
- Local landlord law: security deposit limits, notice periods, eviction procedures, rent regulation, rental registration, and short-term rental rules vary widely by state and city.
- Taxes: rental income is taxable. In the US, residential rental buildings (not land) are generally depreciated over 27.5 years, and special rules apply to rental losses and to sales. Talk to a tax professional before your first year.
- Insurance gaps: make sure your policy covers a rental, and consider liability coverage and requiring renters insurance.
A repeatable deal-analysis checklist
- Decide your criteria first: minimum cash flow, minimum cash-on-cash return, minimum DSCR, and maximum price.
- Collect real numbers (table above) into a spreadsheet template you reuse for every property.
- Calculate EGI, operating expenses, NOI, cap rate, debt service, cash flow, cash-on-cash, and DSCR.
- Stress-test: rent down 10%, vacancy doubled, rate up one point, and a major repair in year one.
- Compare against your criteria, other properties, and the simple alternative of a low-cost index or REIT fund.
- Walk away if it only works in the best case. Most deals should fail your analysis; that's the point of doing it, and why you need a steady supply of leads. Our guide to finding real estate deals covers where they come from.
Frequently asked questions
What is a good cap rate for a rental property?
There's no universal number. Cap rates vary by city, neighborhood, property type, and interest rates. Compare a property with similar properties nearby, and always check cash flow with your real financing, since cap rate ignores the loan.
What's the difference between cap rate and cash-on-cash return?
Cap rate measures the property's income relative to its price, as if bought with cash. Cash-on-cash return measures your annual cash flow relative to the cash you actually invested, so it reflects your financing.
How much should I budget for repairs on a rental?
Many investors budget separately for routine maintenance and for big-ticket capital items, often several percent of rent for each, and adjust for the age and condition of the property. An inspection and the age of major systems are better guides than any rule of thumb.
Is the 1% rule realistic?
It's a quick filter that many properties in expensive markets fail. Use it to screen, then run the full analysis.
Should I buy a rental or invest in REITs?
They suit different people. Direct ownership offers control and leverage but needs more money, time, and risk tolerance. REITs offer diversification and liquidity with much less work. Many people start with funds and buy property later, if at all.
Check your understanding
Answer each question from memory before opening it. Recalling, not rereading, is what makes learning stick (here's why).
1 What is net operating income (NOI), and what does it leave out?
NOI is rental income after vacancy, minus operating expenses such as taxes, insurance, maintenance, capital reserves, and management. It leaves out mortgage payments, so it describes the property, not your financing.
2 A property has NOI of $15,000 and costs $250,000. What is its cap rate?
6%: $15,000 divided by $250,000.
3 Why can a property with a decent cap rate still lose money each month?
Cap rate ignores financing. If the annual mortgage payments are larger than NOI, cash flow is negative even when the cap rate looks fine. That's what happens in this guide's example at a 7% interest rate.
4 What does a DSCR below 1.0 tell you?
The property's NOI doesn't cover its debt payments. You'd have to add money from your own pocket every year, and many lenders won't approve an investment loan below their minimum DSCR.
5 Name two expenses beginners most often leave out of a rental analysis.
Any two of: vacancy, capital expenditures (roof, HVAC, appliances), maintenance, property management, a property tax increase after purchase, or landlord insurance costing more than homeowner's insurance.
Where to go next
You've finished step 1 of the Real Estate path. Next:
- How to find real estate deals: where to find properties worth analyzing, on and off the market, and how to work leads legally.
- Real Estate Development on Coursera (University of Michigan) review: how small development projects come together, including a financial model walkthrough.
- Claude + Zillow: making money through Zillow's Claude connector: AI listing tools, lead flow, and compliance.
- How to analyze data for any project: the general method behind this guide, for any dataset.
Sources
- HUD User: Fair Market Rents: rent reference levels by area.
- US Department of Housing and Urban Development: Fair Housing: protected classes and landlord obligations.
- Consumer Financial Protection Bureau: mortgage shopping tools and loan estimate explanations.
- IRS Publication 527: Residential Rental Property: rental income, expenses, and depreciation.
- Investor.gov: how REITs work and what to check before investing.