House Hacking Taxes: Split Deductions on a Duplex

Marcus, a single 31-year-old software engineer in Columbus, Ohio, buys a $400,000 duplex with a $320,000 mortgage at 6.5%. He lives in the left unit and rents the right unit — identical 1,200-square-foot layouts — for $1,800/month, or $21,600/year. Because the units are equal, his allocation is a clean 50%. That single number does all the work. Half of his ~$20,800 in mortgage interest, half of his $8,000 property tax, half of his $2,400 insurance, and half of the shared utilities shift off his personal Schedule A and onto Schedule E — where none of it hits the $10,000 SALT cap or the $750,000 mortgage-interest cap. Layer in $5,818 of annual depreciation on the rental half of the building, and Marcus reports a small paper loss on $21,600 of real rent collected. He shelters the income and keeps the cash.

That is the entire game. House hacking is not a special tax regime — it is the ordinary rental rules applied to part of the home you live in. The lever you control is the allocation percentage and how cleanly you can defend it.

The one decision that drives everything: your allocation method

Every shared expense on a house hack gets multiplied by your rental percentage. IRS Pub. 527 permits any reasonable method; the two that survive scrutiny are:

• Unit count. A duplex with two equal units is 50% rental. A triplex where you occupy one of three identical units is 33.3% rental. Simple and clean when the units are comparable.
• Square footage. Better when units differ in size. If you live in a 1,680-sq-ft unit and rent a 720-sq-ft unit in a 2,400-sq-ft building, the rental share is 720 ÷ 2,400 = 30%.

Pick the method that reflects reality, document it, and use it consistently every year. Switching methods to manufacture a bigger deduction is exactly the kind of inconsistency an examiner flags. Measure once, write it down, and apply that ratio to every line.

Three buckets, not one

Not every dollar gets the allocation ratio. Sort costs into three buckets:

1. 100% rental (Schedule E in full): a repair to the tenant’s dishwasher, paint for the rental unit, advertising for the vacancy, the tenant’s portion of a separately metered utility.
2. 100% personal (Schedule A or nondeductible): repairs inside your own unit, your personal furniture, your half of a utility you pay only for yourself.
3. Shared (split by the rental %): mortgage interest, property tax, hazard insurance, roof and exterior repairs, landscaping, common-area utilities, HOA dues. These are the big-ticket items the allocation ratio actually moves.

Marcus’s duplex: the 50/50 worked example

Here is Marcus’s full year, with the shared costs split 50% to Schedule E and 50% to his personal Schedule A. Property basis is $400,000, with $80,000 allocated to land (non-depreciable) and $320,000 to the building.

Schedule E math: $21,600 rent − $10,400 interest − $4,000 tax − $1,200 insurance − $1,600 utilities/maintenance − $5,818 depreciation = a $1,418 paper loss. Marcus collected $21,600 of real cash and reports a deductible loss on it. Meanwhile his personal Schedule A picks up $10,400 of mortgage interest (well under the $750,000-principal interest cap) and $4,000 of property tax (which counts toward, but does not blow through, his $10,000 SALT cap on its own).

Why the uncapped Schedule E share is the real prize

Two ceilings hammer ordinary homeowners. The $10,000 SALT cap (IRC §164(b)(6)) limits how much state and local tax — including property tax — you can itemize on Schedule A. The $750,000 mortgage-interest cap (IRC §163(h)(3)) limits deductible interest to the first $750,000 of acquisition debt on a residence. Neither cap touches Schedule E.

That asymmetry is the whole reason the allocation matters so much. When Marcus moves $4,000 of property tax to Schedule E, that $4,000 is fully deductible against rental income with no SALT cap. His remaining $4,000 of personal property tax plus any state income tax then has the full $10,000 SALT room to work with. In a high-tax state, the difference is larger: a New York or California house hacker whose total property tax runs $16,000 can route half ($8,000) to uncapped Schedule E, leaving only $8,000 to fight for space under the $10,000 cap instead of $16,000 hopelessly over it.

Depreciation: the deduction with no cash cost

Depreciation is the deduction that creates Marcus’s paper loss while he pockets cash. You depreciate only the rental share of the building — never land, never your personal half — using straight-line MACRS over 27.5 years for residential rental property under IRC §168(c).

• Building basis: $400,000 purchase − $80,000 land = $320,000.
• Rental share: $320,000 × 50% = $160,000.
• Annual depreciation: $160,000 ÷ 27.5 = $5,818/year.

One nuance worth flagging: bonus depreciation is back at 100%. The One Big Beautiful Bill Act (OBBBA, July 2025) restored 100% first-year bonus depreciation for qualifying property placed in service after January 19, 2025 — so do not assume a 40% phase-down for 2026. The building shell itself is 27.5-year property and is not bonus-eligible, but shorter-life components a cost-segregation study carves out (5-, 7-, and 15-year property) can be expensed 100% in year one on the rental share. For a modest duplex that is often not worth the study cost; for a larger multifamily house hack it can be.

What most people miss: depreciation you skip still gets recaptured

The single most expensive house-hacking mistake is skipping depreciation to “keep it simple.” The IRS does not care whether you actually claimed it. When you sell, recapture is calculated on depreciation allowed or allowable (IRC §1250). That phrase means the IRS computes recapture on the depreciation you could have taken, even if you never deducted a dollar of it. Skip depreciation and you get the worst of both worlds: no deduction during ownership, full recapture at sale.

So you take the depreciation. Every year. The flip side: unrecaptured §1250 gain is taxed at a maximum federal rate of 25% when you sell. Marcus’s $5,818/year becomes $29,090 of recapture after five years — potentially a $7,272 tax bill at the 25% ceiling. That is not a reason to skip it; it is a reason to model it before you sell and to understand that depreciation is a tax deferral, not a permanent escape. If you 1031-exchange the rental half into another property, you can defer the recapture too.

A second commonly missed item: start-up and first-year costs. The cost to get the rental unit ready — tenant screening, the lease, advertising, a separate utility meter — is deductible on Schedule E in the rental percentage (or fully, if directly attributable to the rental). Repairs are deducted immediately; improvements are capitalized and depreciated. Painting the rental unit is a repair; replacing the roof is an improvement split by your ratio.

Schedule E vs. Schedule C: stay passive

Report your house hack on Schedule E. Long-term residential rental income is passive rental income, not a trade or business, so it escapes the 15.3% self-employment tax. You would only land on Schedule C if you provided substantial services like a hotel — daily cleaning, meals, concierge — which a normal duplex tenancy does not involve. Keeping the activity on Schedule E preserves the passive characterization and the SE-tax exemption.

One caveat on the paper loss: passive activity loss rules (IRC §469) can suspend a rental loss if your modified AGI is high. But there is a $25,000 special allowance for active participation in rental real estate, which fully phases out between $100,000 and $150,000 of MAGI. Marcus, at an engineer’s salary under $100,000, can use his $1,418 loss against ordinary income this year. A higher earner’s loss would be suspended and carried forward until there is passive income or the property is sold.

The sale: blending §121 exclusion with recapture

Selling a house hack is two transactions stapled together. You blend the personal-residence treatment with rental treatment by the same allocation ratio.

Say Marcus sells after 6 years for $520,000 — a $120,000 total gain, split $60,000 personal and $60,000 rental by his 50% ratio. His $60,000 personal gain is fully excluded under §121 (well under the $250,000 single cap). On the rental side, $34,908 of depreciation (6 × $5,818) is recaptured at up to 25%, and the remaining rental gain is long-term capital gain. The exclusion shelters the personal slice; the rental slice pays. Knowing that split in advance lets you decide whether to sell, to 1031-exchange the rental portion, or to move back into the rented unit later to expand the §121-eligible fraction.

Your decision lever: set the allocation correctly before year one

The allocation percentage is the one input you set once and live with for the entire hold. It decides how much interest and tax escapes the SALT and mortgage caps, how much depreciation you bank each year, and how the gain splits at sale. Measure the rental footprint precisely — unit count for equal units, square footage for unequal ones — document it with a floor plan and your method, and apply it to every line item consistently. Then take the depreciation every single year (because recapture hits whether you claim it or not), keep the activity on Schedule E to dodge self-employment tax, and model the §121-plus-recapture blend before you ever list the property. Get the percentage right on day one and the rest of the house hack is just bookkeeping.