Why It Matters
You hear "multifamily" and think apartment buildings. That's half the picture. In real estate investing, multifamily covers everything from a $215,000 duplex you live in while renting the other side to a $14 million, 80-unit complex with on-site management and a commercial mortgage.
The line that matters is four units. Properties with 2-4 units are classified as residential — you can buy them with an FHA loan at 3.5% down, get a conventional mortgage, and use the same appraisal process as a single-family home. The moment a building hits 5 units, it crosses into commercial territory. Different loans. Different appraisal methods. Different down payment requirements — typically 20-30%.
This 4-unit threshold is the single most important classification in real estate investing for beginners. A fourplex is the largest property you can buy with owner-occupied residential financing, which means lower interest rates, smaller down payments, and easier qualification. That's why so many investors start there.
Multifamily also solves the biggest risk in single-family rentals: binary vacancy. When your single-family rental sits empty, you collect $0 and pay 100% of the mortgage from your pocket. When one unit in a fourplex is vacant, the other three still generate income. You're diversified from day one.
At a Glance
- Definition: Any property with 2 or more separate dwelling units, each with its own kitchen, bathroom, and entrance
- Residential multifamily (2-4 units): Qualifies for FHA (3.5% down) and conventional residential loans
- Commercial multifamily (5+ units): Requires commercial financing, appraised by income approach, typically 20-30% down
- The 4-unit line: Largest property eligible for owner-occupied residential financing — the sweet spot for new investors
- Vacancy advantage: Multiple income streams reduce the all-or-nothing risk of single-family rentals
- Scale range: Duplexes, triplexes, fourplexes (small multifamily) through garden apartments, mid-rises, and high-rises (large multifamily)
How It Works
The residential side: 2-4 units. A duplex, triplex, or fourplex is underwritten just like a single-family home. The lender looks at your credit score, debt-to-income ratio, and employment history. They appraise the property using comparable sales — what did similar 2-4 unit buildings sell for recently? You can put down as little as 3.5% with an FHA loan if you live in one unit. Conventional loans typically require 15-25% down for investment properties, but only 5-15% if owner-occupied. The 2025 FHA loan limits for a fourplex reach $967,450 in standard markets and over $1.8 million in high-cost areas.
The commercial side: 5+ units. Once a building hits five units, everything changes. Lenders don't care much about your personal income — they underwrite the property based on its income. The appraisal uses the income approach: Net Operating Income divided by the local cap rate determines value. Down payments jump to 20-30%. Loan terms shift from 30-year fixed to 5-10 year terms with 20-25 year amortization and a balloon payment at maturity. Interest rates run 0.5-1.5% higher than residential. But commercial loans don't count against your personal mortgage limit — you can scale without hitting the Fannie Mae 10-property cap.
The economics of scale. Per-unit costs drop as unit count rises. A property management company charges 8-10% of gross rents on a fourplex but 4-7% on a 50-unit building because on-site staff handle more units per dollar. Insurance per unit drops. Maintenance costs spread across more doors. A new roof on a 12-unit building costs more than a single-family roof, but per-unit it's a fraction. This is why experienced investors graduate from small multifamily to large — the margins improve at scale.
Income diversification. A single-family rental has a vacancy rate of either 0% or 100%. A fourplex at 75% occupancy still covers most of the mortgage. A 20-unit building can absorb two vacancies without the owner feeling financial pressure. The more units you own under one roof, the more predictable your cash flow becomes. Lenders know this — it's one reason commercial multifamily gets favorable debt terms despite higher rates.
Real-World Example
Natasha Singh finds a triplex listed at $387,000 in a B+ neighborhood. All three units are occupied — two 2-bedroom units at $1,150/month each and one 1-bedroom at $875/month. Gross monthly rent: $3,175.
Natasha plans to live in the 1-bedroom and rent out both 2-bedrooms. Because she's owner-occupying, she qualifies for an FHA loan at 3.5% down:
- Down payment: $13,545
- Monthly mortgage (P&I + PMI): $2,410
- Monthly expenses (taxes, insurance, repairs, vacancy reserve): $635
- Total monthly cost: $3,045
- Rental income from 2 units: $2,300/month
Natasha's out-of-pocket housing cost: $3,045 - $2,300 = $745/month. She was paying $1,425/month renting a comparable apartment. She just cut her housing expense by $680/month while building equity in a $387,000 asset.
When she moves out after the FHA's 12-month occupancy requirement, she rents the 1-bedroom for $875. Now gross rent hits $3,175/month against $3,045 in costs. The triplex cash flows $130/month — modest, but she bought it with $13,545 down and lived nearly free for a year.
Compare this to a single-family rental at the same price point. A $387,000 single-family renting for $2,100/month would require 20% down ($77,400) as an investment property, and the cash flow would be similar. Natasha got into multifamily for one-sixth the capital — and she diversified across three tenants instead of depending on one.
Pros & Cons
- Lower barrier to entry with FHA financing — Buy a 2-4 unit property with 3.5% down by living in one unit, while collecting rent from the others to offset your mortgage
- Built-in vacancy protection — Multiple income streams mean one empty unit doesn't zero out your revenue, unlike a single-family rental where vacancy equals 100% lost income
- Economies of scale on operating costs — Per-unit expenses for management, insurance, and maintenance decrease as unit count rises, improving margins at scale
- Faster portfolio growth — Buying one fourplex gives you four doors in a single transaction instead of four separate single-family purchases with four closings, four inspections, and four loans
- Income-based appreciation for 5+ units — Commercial multifamily values are tied directly to NOI, so raising rents or cutting expenses directly increases property value — something you control
- Higher complexity and management burden — More units mean more tenants, more maintenance requests, and more turnover cycles to coordinate, especially without professional management
- Commercial financing barriers at 5+ units — Crossing the 5-unit threshold requires 20-30% down payments, balloon payments, and income-based underwriting that can disqualify properties with thin margins
- Tenant concentration risk — All your units share one roof, one foundation, and one location — a major structural issue, flood, or neighborhood decline affects every unit simultaneously
- Higher entry cost in absolute dollars — Even with better per-unit economics, a $387,000 triplex requires more capital than a $185,000 single-family, and large multifamily can run into the millions
- More regulatory exposure — Multi-unit buildings face stricter fire codes, habitability requirements, and municipal inspections than single-family homes, adding compliance costs
Watch Out
Know exactly where the 4-unit line falls. The difference between a fourplex and a fiveplex isn't one unit — it's an entirely different financing universe. A fourplex qualifies for FHA at 3.5% down with a 30-year fixed rate. A fiveplex requires a commercial loan at 20-30% down with a 5-10 year balloon. If you're looking at a property advertised as "5 units," verify whether one of those units is actually a non-conforming conversion that could be reclassified. Conversely, don't assume a "4-unit" building meets FHA standards — each unit needs a separate kitchen, bathroom, and entrance to qualify.
Don't underwrite 2-4 units like a commercial property. New investors sometimes value small multifamily using cap rates and NOI. That's how 5+ unit buildings are appraised. Residential multifamily (2-4 units) is appraised by comparable sales — what similar buildings sold for, not what income they produce. Your duplex might generate a beautiful 8% cap rate, but if comps show $285,000, that's your value. You can't force appreciation on residential multifamily by raising rents.
Factor in the management transition. Self-managing a duplex is straightforward. Self-managing a 12-unit building is a part-time job. Most investors underestimate the jump in complexity between 4 and 12 units — more tenants, more turnover, more maintenance coordination. Budget for professional management from the start if you're buying 5+ units, and build a realistic management fee into your underwriting even for smaller properties.
Ask an Investor
The Takeaway
Multifamily property is the broadest category in real estate investing, spanning everything from a duplex you house-hack with 3.5% down to a 200-unit apartment complex financed with commercial debt. The critical distinction is four units: below that line, you're in the residential financing world with low down payments, 30-year fixed rates, and comp-based appraisals. Above it, you enter commercial territory with income-based valuations, larger down payments, and balloon terms. For most new investors, the 2-4 unit sweet spot offers the best combination of accessible financing, built-in vacancy protection, and a path to scaling — it's how you buy four doors in one transaction with less capital than a single investment-property purchase. Start small, learn the management realities on a duplex or triplex, and the jump to commercial multifamily becomes a decision about scale, not about learning a new asset class.