Buying a duplex, triplex, or fourplex can be one of the smartest real estate investments you make—but only if you know how to properly analyze the deal before you buy.
Too many investors rely entirely on online calculators or software to tell them whether a property makes sense. While those tools can be helpful, they often hide the “why” behind the numbers. Understanding how the financial analysis actually works will help you make better investment decisions and avoid expensive mistakes.
Whether you’re looking at a property in Portland, Bend, Salem, Eugene, or anywhere else in Oregon, here’s a straightforward way to evaluate a small multifamily investment from the ground up.
Step 1: Calculate Your Gross Rental Income
Every deal analysis begins with income.
Start by listing the monthly rent for each unit.
For example:
- Unit 1: $1,500
- Unit 2: $1,550
- Unit 3: $1,475
This gives you total monthly rent of $4,525, or $54,300 annually.
Don’t forget to include any additional sources of income, such as:
- Coin-operated laundry
- Parking fees
- Storage rentals
- Utility reimbursements
These smaller revenue streams can have a meaningful impact on the property’s overall performance.
Step 2: Estimate Operating Expenses
The next step is identifying every expense required to operate the property.
This is where many new investors underestimate costs.
Common operating expenses include:
Property Taxes
Taxes are easy to verify through the county assessor’s office or websites like Portland Maps. Since tax bills are annual, divide the annual amount by 12 to determine your monthly expense.
Insurance
Contact an insurance agent for a quote before writing an offer. Insurance premiums vary significantly depending on the property’s age, condition, and location.
Utilities
Determine which utilities are landlord-paid and which are tenant-paid.
Typical expenses include:
- Water and sewer
- Garbage
- Common area electricity
- Common area gas (if applicable)
Many Oregon duplexes and triplexes have separately metered electric service, meaning tenants pay their own electric bills. Water and sewer, however, are often paid by the owner unless the property has separate meters.
Never assume—always verify.
Step 3: Include Management Costs
Even if you plan to manage the property yourself, it’s smart to budget for professional management.
Why?
Because your time has value.
If life circumstances change—or you simply decide you’d rather hire someone later—you’ll already know whether the investment still works financially.
A typical management fee is around 8% of gross rental income.
Think of this less as an expense and more as assigning value to your own time.
Step 4: Budget for Vacancy
No rental property stays occupied 100% of the time forever.
Units occasionally sit vacant while you:
- Advertise
- Clean
- Repair
- Screen tenants
A common vacancy assumption is around 5% of gross rents.
If you’re buying in a particularly desirable neighborhood with consistently high demand, your actual vacancy may be lower. Conversely, weaker rental markets may require a larger vacancy allowance.
The goal isn’t to predict the future perfectly—it’s to be conservative enough that you’re prepared.
Step 5: Account for Repairs and Maintenance
Every property requires maintenance.
Repairs might include:
- Plumbing leaks
- Appliance repairs
- Electrical issues
- Minor carpentry
- Paint touch-ups
A useful starting point is budgeting approximately 5% of gross rental income annually for repairs.
Older properties may require more.
If you’re handy and perform repairs yourself, your costs may be lower. If you hire contractors for everything, plan accordingly.
Whenever possible, ask the current owner for maintenance records to better estimate future expenses.
Step 6: Save for Capital Expenditures
One mistake many first-time investors make is confusing repairs with capital improvements.
Repairs are routine.
Capital expenditures (often called “CapEx”) are major replacements, including:
- Roofs
- HVAC systems
- Water heaters
- Exterior painting
- Windows
These don’t happen every year, but they eventually happen to every property.
Rather than being surprised by a $15,000 roof replacement someday, smart investors set aside money every month.
Exactly how much depends on the property’s age and condition, but the important thing is to plan ahead.
Step 7: Calculate Net Operating Income (NOI)
After subtracting all operating expenses from your gross income, you arrive at one of the most important figures in commercial real estate:
Net Operating Income (NOI).
NOI represents how much income the property generates before debt payments.
This number allows investors to compare properties objectively regardless of financing.
Step 8: Add Your Mortgage Payment
Only after calculating NOI should you consider financing.
One important note:
Use only the principal and interest portion of your mortgage payment.
Don’t include taxes and insurance if you’ve already counted them as operating expenses, or you’ll accidentally double-count those costs.
Subtract your mortgage payment from NOI to determine your monthly cash flow.
Many investors are surprised that Oregon duplexes and triplexes don’t produce massive monthly cash flow.
That’s perfectly normal.
Understanding the Numbers That Matter
Once your analysis is complete, several important metrics can help you evaluate the investment.
Expense Ratio
Expense Ratio measures operating expenses as a percentage of gross rental income.
Many well-performing small multifamily properties fall somewhere around 35%, although every property is different.
Lower is generally better—but only if you’re not underestimating future expenses.
The 1% Rule
The famous 1% Rule suggests monthly rent should equal approximately 1% of the purchase price.
In many Oregon markets, quality duplexes and triplexes simply don’t meet this rule.
That doesn’t automatically make them poor investments.
Oregon investors often prioritize appreciation, stable rental demand, long-term wealth building, and tax advantages over immediate cash flow.
Gross Rent Multiplier (GRM)
Gross Rent Multiplier compares purchase price to annual gross rents.
Generally speaking:
- Lower GRM = better value for buyers
- Higher GRM = stronger pricing for sellers
Rather than focusing on a perfect number, compare GRMs between similar properties in the same market.
Cap Rate
Cap rate is one of the most widely discussed investment metrics.
It measures the relationship between Net Operating Income and the purchase price.
Unlike cash flow, cap rate ignores financing entirely.
That’s what makes it useful.
Whether an investor pays cash or finances 95% of the purchase, everyone calculates cap rate the same way.
For Oregon small multifamily properties, cap rates are often lower than in many other states because investors are willing to pay more for desirable locations and long-term appreciation potential.
Cash-on-Cash Return
Finally, calculate your cash-on-cash return.
This measures how much annual cash flow you’re earning relative to the actual cash you invested for your down payment.
While some investors focus heavily on this number, remember it’s only one piece of the puzzle.
A property with modest cash flow today may still become an exceptional investment because of:
- Rising rents
- Appreciation
- Mortgage paydown
- Tax benefits
- Increased equity over time
Looking at only one metric rarely tells the whole story.
The Bottom Line
Analyzing a duplex, triplex, or fourplex isn’t about finding one magic number that says “buy” or “don’t buy.”
Instead, it’s about understanding how all the pieces fit together.
By carefully evaluating income, expenses, Net Operating Income, cash flow, cap rate, expense ratio, and cash-on-cash return, you’ll gain confidence in your investment decisions and avoid surprises after closing.
If you’re considering buying or selling a duplex, triplex, or fourplex anywhere in Oregon, I’d be happy to help you analyze the numbers and determine whether the property truly fits your investment goals. A careful analysis today can save you thousands of dollars—and help you build long-term wealth with confidence.
