A client came to me recently with a setup I hadn't written about before. He was looking at a lake house. The plan was to live in it part of the year while his kids were still young, rent it on Airbnb the rest of the time, and then in a couple of years move out and run it as a full short-term rental.
His real question was about depreciation. How does it work while he's still using the place himself, and do the deductions he can't use in the early years come back to him later?
This is house hacking. It's just applied to a short-term rental instead of a duplex. The play is real, and most investors aren't thinking about it. But the depreciation math has a trap in it, and that's what I want to talk through in this post.
House hacking, applied to a short-term rental
Most people know the classic version. You buy a multi-unit property, live in one unit, and rent the others to cover the mortgage. Fewer people think about buying a single property they'll live in now and convert to a full short-term rental later. You get a home while your family needs one, and you set up a rental business for when they don't.
The catch is that the tax treatment isn't static. It changes year to year as your use of the property changes. So the depreciation you can take in the year you're living there looks very different from the depreciation you can take once you've moved out.
While you're living in it: personal use turns it into a "residence"
The first thing to understand is the line the IRS draws under Section 280A. Your property becomes a "dwelling unit used as a residence" in any year your personal use exceeds the greater of 14 days or 10% of the days it's rented at a fair rental price.Say you rent it 90 days at fair market rates during the year. Ten percent of 90 is 9 days, but the statutory floor is 14, so your threshold is 14. If you personally use the place 60 days, you're well over the line. For that year, the vacation-home rules apply.
That doesn't mean you lose depreciation entirely. You can still depreciate the property. But you can only depreciate the rental-use percentage. The personal-use portion gets nothing.
How Section 280A caps what you actually deduct
Even on the rental-use portion, the deduction is capped. Section 280A(c)(5) says your rental deductions can't exceed the rental income from the property. You can't use the rental to throw off a loss in a year you're treating it as a residence.
The deductions also come in a fixed order:
- First, mortgage interest and property taxes
- Then operating expenses like utilities, cleaning, repairs, and insurance
- Last, depreciation
Because depreciation sits at the bottom of the stack, it's the first thing squeezed out when you run out of rental income to absorb it.
A quick example.
- Say the property throws off $25,000 of gross rental income for the year.
- Allocable interest and taxes come to $4,000, and operating expenses come to $15,000.
- That leaves $6,000 of income for depreciation to work with.
- If your rental-use depreciation for the year is $30,000, you deduct $6,000 of it.
- The other $24,000 doesn't disappear, but you don't get it this year either. It becomes a Section 280A carryforward.
The trap: that carryforward is not a passive loss
This is the part my client wasn't sure about. People expect that stranded depreciation (the Section 280A carryforward from the previous example) behaves like a suspended passive loss. The story goes: it sits on the shelf, and once you go full short-term rental or qualify as a real estate professional, it gets released and offsets your other income.
Unfortunately, that's not how it works.
A Section 280A carryforward stays in the Section 280A world. The code keeps these dwelling-unit items out of the passive activity loss system entirely, and the carryforward stays tied to that same property and stays subject to the same income cap, even in later years after you've stopped living there. So it can only ever offset future net rental income from that property. It never becomes a deduction against your W-2 income, no matter how the activity is treated later.
That's different from a true passive loss under Section 469. A passive loss can free up when you have passive income or when you sell the activity in a fully taxable sale. A Section 280A carryforward doesn't get that treatment. Moving out later doesn't turn it into an active loss, and there's no clear authority that a sale releases it — plan on it being usable only against that property's future rental income.So crossing the personal-use threshold doesn't "suspend and release" your depreciation. It strands it.
One consolation: depreciation disallowed under the income cap doesn't reduce your basis. Only depreciation actually allowed does.
After you convert to a full short-term rental
Now after buying the property, move the calendar forward. My client moves out. No personal use. The average guest stay is seven days or less, and he materially participates in running the property.
At that point the analysis changes. A rental where the average stay is seven days or less isn't treated as a "rental activity" under the passive loss rules. If he materially participates, the activity is nonpassive, and current-year losses can offset active income. This is the actual short-term rental loophole, and it's powerful.
But two things still hold. The Section 280A cap governed the earlier year. And the carryforward from that year stays parked exactly where it was, usable only against that property's rental income.
When to run the cost segregation study
A natural instinct is to run the cost segregation study the year you buy the property or in the first full short-term rental year. The instinct is reasonable, but the study isn't the lever people think it is.
A cost segregation study doesn't place property in service. It reclassifies costs into shorter-lived categories that bonus depreciation can write off immediately. It can't move an asset's placed-in-service date. A property is placed in service when it's first ready and available for rent, and bonus depreciation belongs to that year. In other words, the placed in service date is the date it is converted into a rental property and no longer a primary residence or 280A vacation home. So the year that matters is the year you start renting, not the year you order the study.
That's what decides everything. If you run a cost segregation study in a year Section 280A governs the property, the accelerated deductions land inside the cap. You deduct up to your rental income, and the rest becomes a carryforward locked to that property. You paid for a study to generate a deduction you can't use and can never move.
So the sequence is: keep depreciation small while the property is a residence under Section 280A, and don't run a study until it's placed in service as a rental. Then take everything.
The switch flips at the conversion date, not January 1
The natural worry about a mid-year conversion is proration — that if you live there through April and rent from May, you only get eight-twelfths of the deduction. That's not how it works.
Section 280A(d)(4) creates a qualified rental period: a consecutive stretch of 12 months or more when the property is rented or held for rental at a fair rental price. If you used the property as your principal residence before that period starts, those personal-use days don't count against you. The year isn't split. The property converts on the date the qualified rental period begins.
Two conditions, and both matter. The 12 months have to be consecutive, which means it has to run past year-end. You can't rent for the last two weeks of December, call it converted, and move back in come January. And the rule covers use as your principal residence, not personal use generally.
On the way out: recapture and Section 121
Cost segregation accelerates deductions going in, and it adds complexity coming out. The short-life components you broke out are generally subject to Section 1245 recapture as ordinary income on sale, and depreciation on the building comes back as unrecaptured Section 1250 gain, taxed at up to 25%.
If the property was your principal residence for two of the five years before you sell, Section 121 can exclude up to $250,000 of gain, or $500,000 if you're married filing jointly. But the exclusion doesn't reach depreciation. Section 121(d)(6) carves out gain attributable to depreciation claimed after May 6, 1997, and that amount is taxable no matter how cleanly you meet the two-out-of-five-year test. On a property you've cost segregated, Section 121 shelters your appreciation. The depreciation you claimed still comes back as recapture.
There's a second limit. Section 121(b)(5) reduces the exclusion for "nonqualified use," meaning any period after 2008 when you owned the property but weren't using it as your principal residence or for rental use. Gain allocated to that period is prorated out of the exclusion based on nonqualified use over your total ownership period.
Order matters here too. Rental use after the last date you used the property as your principal residence isn't nonqualified use, so if you live in it first and convert it to a rental afterward, those rental years don't cut into the exclusion. Renting the property before it becomes your principal residence is what creates nonqualified use, and that version prorates your gain over the entire time you owned it.
The takeaway
House hacking a short-term rental works, but the depreciation rewards planning, not improvisation. The deductions you strand in a personal-use year don't come back as active losses later. They stay locked to that property and that income. So the move is to decide up front which year you want the big deduction in, and make that year a clean rental year — no personal use, or a qualified rental period that starts before the study and runs past year-end.
If you're thinking about a property like this, the timing of the study and the timing of your personal use both matter, and they need to line up. That's the kind of thing worth mapping out before you close, not after. If you want help running the numbers, that's what we do.
