FHA is the reason house hacking is reachable at all: 3.5% down on a building with up to four doors, one loan, one deed, owner-occupant pricing. It's the same mortgage a first-time homebuyer uses on a plain house, pointed at an income property instead.
The rules take an afternoon to learn. The arithmetic is where deals die: on three- and four-unit properties FHA runs a test almost nobody mentions until the appraisal lands, and a triplex that looks fine on a spreadsheet can fail it by $200 a month. What follows — what FHA allows, that test worked end to end, the county ceiling that scales with unit count, what mortgage insurance really costs, a fourplex on a receipt, and when a 5% conventional loan wins instead.
what FHA actually allows on one to four units
FHA's published floor for 3.5% down is a 580 credit score, with 10% down between 500 and 579 — but lender overlays routinely sit above the published floor, so treat the mid-600s as the practical number and shop more than one lender. The down payment doesn't change with unit count: a fourplex at 3.5% down is the same program as a single-family at 3.5% down.
Occupancy is the price of that pricing. You move in within roughly 60 days of closing and live there at least 12 months, and you get one FHA loan at a time — exceptions are narrow and documented, and your lender decides whether you fit one. Signing that you intend to occupy a property you won't live in is occupancy fraud on a federally backed loan.
Occupying also helps you qualify: lenders count a share of the appraiser's market-rent estimate on the units you don't live in — commonly around 75% — as income against your debt-to-income ratio. That is a different calculation from the one in the next section, and confusing the two is the most common mistake investors make reading about FHA multifamily.
the self-sufficiency test almost nobody mentions
On three- and four-unit properties, FHA requires the property to carry itself. The lender takes the appraiser's fair-market rent for every unit in the building — including the one you're going to live in — subtracts the greater of the appraiser's vacancy and maintenance estimate or 25%, and compares what's left to the full monthly payment: principal, interest, taxes, insurance, and FHA mortgage insurance. That net rent has to cover 100% of the payment. Not 90%, and not "close enough with your income backing it up." Duplexes are exempt entirely, which is the biggest reason a duplex is the most common first FHA house hack.
Worked, with round numbers. You're under contract on a $370,000 triplex and the full payment lands around $3,125/mo once taxes, insurance, and MIP stack onto principal and interest. All three units appraise at $1,300 of market rent, yours included — $3,900/mo gross, which feels comfortable against $3,125. Apply the haircut and the lender counts $2,925: $200/mo short, and the deal is dead on an FHA loan no matter how strong your income is.
Three fixes. Pay less — the right-hand column above is the same building at $340,000, and it clears. Buy the rate down with points or a seller-paid buydown, because the test runs on the payment and the payment runs on the rate. Or buy a duplex, where the test doesn't apply. What doesn't work is arguing; the ratio is mechanical.
Two things to settle with your lender before you write the offer: which rent figure the appraiser will use, and whether their vacancy and maintenance estimate comes in above 25%, because the higher number is the one that applies. On a deal this tight either one is the difference between passing and failing, and a loan officer can answer both in one call. Note too that passing means FHA will fund the loan — not that the building is a good buy.
the county ceiling scales with unit count
FHA loan limits are published per county and per unit count, and the spread is wider than most buyers expect: in the same county, the four-unit ceiling lands at roughly double the one-unit number. So in an expensive metro where a single-family house is priced well past the FHA one-unit limit, a fourplex at double that limit is still financeable at 3.5% down. The bigger building is the one that stays inside the program.
The limits reset annually, so a figure you read last year is stale, and they're county-level — a metro straddling a county line can carry two different ceilings twenty minutes apart. Look up your target counties before you shop.
what MIP really costs
FHA mortgage insurance comes in two pieces, and both are permanent features of the deal. The upfront premium is around 1.75% of the loan, almost always financed into the balance — on a $400,000 purchase that's roughly $6,800 added to what you owe on day one, quietly offsetting part of the equity your down payment bought. Then the annual premium, roughly half a point of the balance per year billed monthly, which at 3.5% down lasts the life of the loan and does not fall off at 20% equity. The only way out is a refinance.
So model that refinance from day one. Once paydown and appreciation put you comfortably past 20% equity, moving to a conventional loan drops the premium entirely — on a four-unit balance that's real money every month. It isn't free: closing costs, a fresh appraisal, and a rate that has to cooperate. Put it in the underwriting as a planned step with a trigger, not a vague someday. Rates run around 7% as of late 2026 and move constantly, so treat any rate you read as a moving target.
a fourplex, on a receipt
Round numbers again. A $400,000 fourplex at 3.5% down is about $14,000 down plus roughly $10,000 of closing costs — $24,000 to control four doors. The full payment with taxes, insurance, and MIP lands near $3,500/mo. All four units appraise at $1,200, so the test counts four doors at 75% — $3,600 — and the building clears by $100. You live in one unit and the other three pay $3,600/mo, which covers the whole payment and leaves about $100 over, against the $1,200 a comparable unit would cost you to rent down the street.
That isn't luck, it's the test. Three quarters of four even rents is exactly the gross rent of the other three doors, so on a fourplex, clearing self-sufficiency and having your tenants cover your payment are the same sentence said twice. A fourplex that passes houses you for about nothing on paper; one that fails was never going to.
Two honest asterisks. That $100 of slack assumes full occupancy — one vacant unit swings it by $1,200 a month while the payment stays the same, so hold reserves on top of the $24,000, not inside it. And that $24,000 becomes the denominator on your return the day you move out and all four doors rent; the cash-on-cash calculator turns it into a percentage you can compare against anything else you'd do with the money.
The rent assumptions carry the whole model, so pressure-test them against more than one source. Where vouchers are common, HUD's published Fair Market Rents by state, metro, and ZIP are a useful second reference — with the caveat that an FMR is a gross rent covering rent plus tenant-paid utilities, so a landlord's contract rent sits below it by the local utility allowance, and what a voucher pays turns on the housing authority's payment standard and its own rent reasonableness finding. Varies by PHA. Read it as a benchmark, never a promised number.
The worked examples above are illustrative — these are not. Three listings from the catalog right now, already underwritten by the same engine a subscriber searches with. Open any of them on Zillow and check the numbers yourself.
FHA vs 5% conventional on the same house hack
Conventional financing now reaches 5% down on owner-occupied two-to-four-unit properties, which makes this a real decision. The trade is 1.5 points of down payment against permanent mortgage insurance: conventional PMI drops off as the loan amortizes toward roughly 80% of value, while FHA MIP at 3.5% down never does. Over a long hold the cheaper loan is usually conventional; over a short runway to your first deal, it's the one you can actually fund.
- Cash is the binding constraint and it's a duplex: FHA. No self-sufficiency test, and 1.5 points of price is money you don't have.
- Your 3-4 unit fails self-sufficiency: conventional, which has no equivalent test — the triplex FHA rejected may fund at 5% down.
- Thin credit or a messy file: FHA, which is more forgiving on score and on recent credit events.
- You can clear 5% down and expect to hold past five years: conventional. Avoiding life-of-loan MIP usually outweighs the extra cash at closing.
Price both. Ask each lender for the full payment including mortgage insurance, the cash to close, and — on a three or four unit — whether the FHA option clears self-sufficiency at your contract price.
the 12-month exit, and doing it again
Once you've genuinely served the occupancy year, the building converts: you move out, rent your old unit, and every door produces income — on a fourplex, three rents become four without buying anything. FHA doesn't call the loan when you leave after the occupancy period is honestly satisfied.
Then you repeat, with one constraint — one FHA loan at a time. Unless you qualify for a documented exception, the next house hack goes on a conventional owner-occupied loan at 5% down, or on FHA again once you've refinanced the first building out of it. The broader strategy, including the versions that aren't small multifamily, is in the house hacking guide. Before any of it, underwrite the specific building — including the self-sufficiency ratio if it has three or four doors. The rental property analyzer models that payment stack against market rent on any active listing, which is how you learn a deal fails the test on a Tuesday afternoon instead of three weeks and an appraisal fee later.