By Virtual Cost Segregation
The best cost segregation study provider for rental property investors
Built to IRS standards
Audit support includedFlat price for every study3 to 5 business days Cost segregation for unmarried co-owners of rental property works the same way it works for any other ownership structure at the engineering level, but the tax benefit splits by ownership percentage instead of flowing through one household return. Two people who bought a short-term rental together but never married need to plan the allocation and the material participation test separately, and that planning has to happen before the study, not after.
- Unmarried co-owners split cost segregation deductions by ownership percentage, not by household filing status.
- Each co-owner needs a separate material participation test if using the STR loophole to offset W-2 income.
- A tenancy-in-common structure reports depreciation on each owner's own Form 4562; an LLC taxed as a partnership issues K-1s that already reflect the split.
- One engineering-based study covers the whole property. Order it once, not per owner.
- Bonus depreciation is 100% permanent under OBBBA for residential rental property acquired and placed in service after January 19, 2025, regardless of how many names are on the title.
Why cost segregation matters for unmarried co-owners
Married couples filing jointly get IRS-recognized shortcuts that unmarried co-owners do not. Spouses can combine hours to clear the STR loophole's material participation test. Unmarried co-owners cannot. Each person on the title has to independently document 100+ hours and prove they worked more on the property than anyone else, including their co-owner, if they want to use accelerated depreciation to offset their own W-2 income.
That single distinction changes how you structure ownership before a cost segregation study. Get the ownership percentage and the participation records straight first. The engineering side of the study, the reclassification of building components into 5-year, 7-year, and 15-year property, works identically whether one person owns the property or four unmarried co-owners split it evenly.
A cost segregation study is not a CPA service and it is not filed with the IRS directly. It is a supplementary, audit-defensible report that each co-owner's own CPA applies when preparing that owner's return. For unmarried co-owners, that usually means two or more separate CPAs implementing the same underlying report on different tax returns.
Confirm the ownership structure before you order the study
Get this documented before the property goes under a cost segregation study, not after.
- Confirm whether title is held as tenants in common, joint tenants, or inside an LLC or partnership
- Get the ownership percentage in writing, whether that's the deed, the operating agreement, or a partnership agreement
- Confirm how the entity is taxed: disregarded entity, partnership, or S-corporation
- Note each co-owner's W-2 income and marginal bracket, since the STR loophole's value depends on it
- Flag any co-owner who is a purely passive investor with no plans to materially participate
Confirm the property qualifies as a residential rental
Virtual Cost Segregation studies residential rental property only, meaning short-term rentals, long-term rentals, single-family homes, duplexes, and similar residential types. Commercial property types are outside scope.
- Airbnb, VRBO, and other short-term rental units
- Long-term single-family and small multi-unit residential rentals
- Duplexes, triplexes, and fourplexes held for rental income
- Vacation rentals with mixed personal and rental use, evaluated on the rental-use percentage
- Accessory dwelling units rented as part of the property
Order one engineering-based study for the property, not one per owner
Unmarried co-owners sometimes assume each person needs a separate report. They don't. One study covers the whole building and its site improvements.
- A single engineering-based cost segregation study documents the entire property's components
- No site visit is required for most residential cost segregation studies, which keeps the process workable across co-owners in different cities
- Turnaround typically runs 3-5 business days once documents are submitted
- The report runs 100+ pages and documents the reclassification methodology in detail for audit defense
- The flat fee is $2,200 regardless of how many owners are on the title
Allocate the reclassified percentage across ownership shares
Here's where the math actually happens. Assume a property with a $500,000 depreciable basis and a cost segregation study that reclassifies 25% of that basis, or $125,000, into shorter recovery periods. Two unmarried co-owners splitting the property 50/50 each get $62,500 of accelerated basis. A co-owner in the 37% tax bracket who can use that basis against W-2 income in 2026 is looking at a meaningfully different outcome than a co-owner in a lower bracket who can only use it against passive income.
The allocation math is simple once the ownership percentage is documented. The mistake is skipping the documentation step and assuming a 50/50 split when the actual ownership percentage, the one on the deed or operating agreement, says otherwise. Review how to allocate cost segregation benefits among partners before the study closes to confirm the split matches the legal ownership record.
Test material participation separately for each co-owner
This is the step unmarried co-owners get wrong most often, usually because they assume the rules work like they do for a married couple.
- Track each co-owner's hours independently using separate time logs, not one shared log
- The 100-hour test and the "more time than anyone else" test both apply per person, not per household
- Unlike spouses filing jointly, unmarried co-owners cannot combine hours to clear either test
- A co-owner who fails material participation still benefits from bonus depreciation, just as a passive loss carried forward rather than a current-year offset against W-2 income
- Keep documentation (calendars, guest communication logs, maintenance records) that would hold up if the IRS asks who actually ran the property day to day
Hand the report to each co-owner's own CPA
One report, multiple implementations. This is where unmarried co-owners diverge from a married-filing-jointly household using a single return.
- If the property is held as tenants in common, each owner's CPA applies their percentage of the reclassified basis independently on that owner's own Form 4562
- If the property is held in an LLC taxed as a partnership, K-1s should already reflect each partner's allocated share of bonus depreciation before anyone files
- Confirm both CPAs are using the same placed-in-service date and the same reclassification percentages from the underlying report
- If one co-owner's CPA has questions about the engineering methodology, the report is built to answer them without a second study
Get a flat-fee study for your rental
One $2,200 report, delivered in 3-5 business days, no site visit required.
Comparing ownership structures for unmarried co-owners
| Structure | Best for | Reporting mechanism | Key limitation |
|---|---|---|---|
| Tenancy in common | Two or more unrelated owners who want independent tax treatment | Each owner reports their percentage on their own Form 4562 | No liability shield; each owner's creditors can reach the shared property |
| LLC taxed as a partnership | Co-owners who want liability protection and a single K-1 process | K-1s allocate bonus depreciation by ownership percentage | Requires a partnership return and an operating agreement that spells out the split |
| LLC taxed as a disregarded entity | A single owner using an LLC for liability protection, not a true co-ownership | Flows through to one owner's personal return | Doesn't fit true unmarried co-ownership with two or more real owners |
| General partnership | Informal co-ownership without a separate entity | Partnership return with allocated K-1s | Offers no liability protection; rarely the right long-term structure |
Verdict: unmarried co-owners planning to use the STR loophole independently are usually better served by an LLC taxed as a partnership, since it forces the ownership percentage into writing and produces K-1s that already carry the correct allocation into each owner's return.
Common mistakes unmarried co-owners make
- Assuming they can combine hours like spouses can. The material participation combination rule applies to married filing jointly, not to unmarried co-owners, no matter how the property is run day to day.
- Splitting the study cost 50/50 without confirming ownership matches. A co-owner who put up 60% of the purchase price but agreed to split the report fee evenly should still get 60% of the reclassified basis, not 50%.
- Ordering separate studies per owner. One property needs one engineering-based cost segregation study. Duplicate studies waste money and can create conflicting reclassification numbers between owners.
- Not updating the ownership record after a buy-in or buyout. If a third person buys into the property in 2026, the operating agreement and the depreciation allocation both need to reflect the new percentage before that year's return is filed.
- Letting one CPA implement the report without looping in the other owner's CPA. Both returns need to agree on the placed-in-service date and reclassification percentages, or the study becomes an audit flag instead of an audit defense.
FAQ
Can unmarried co-owners split a cost segregation study's benefits?
Yes. The reclassified depreciation splits according to each owner's percentage of the property as recorded on the deed or operating agreement, not by an assumed even split. One engineering-based study covers the whole property regardless of how many owners hold title.
Do unmarried co-owners need separate cost segregation studies?
No. A single study documents the property's components and reclassified basis. Each co-owner's own CPA then applies that owner's percentage share to their individual or partnership return.
Can unmarried co-owners combine hours for the STR loophole's material participation test?
No. Only spouses filing a joint return can combine hours under IRS rules. Unmarried co-owners must each independently clear the 100-hour test and the "more time than anyone else" test.
What structure works best for unmarried co-owners of a short-term rental?
An LLC taxed as a partnership generally works best because it forces the ownership percentage into a written operating agreement and produces K-1s with the depreciation allocation already applied.
How much does a cost segregation study cost for co-owned rental property?
Virtual Cost Segregation's flat-fee residential study runs $2,200 regardless of how many names are on the title, with delivery typically in 3-5 business days.
Does bonus depreciation still apply if only one co-owner materially participates?
Yes. Bonus depreciation applies to the property's reclassified basis regardless of participation status. A co-owner who doesn't materially participate still gets the deduction, but as a passive loss rather than an offset against their own W-2 income.
What happens if unmarried co-owners split ownership unevenly?
The reclassified depreciation follows the documented ownership percentage, so a 70/30 split on the deed produces a 70/30 split of the accelerated depreciation, not an even division.
Is a cost segregation study filed with the IRS?
No. The report is a supporting document each co-owner's CPA uses when preparing that owner's own tax return. It is not filed directly with the IRS but should be kept on hand in case of an audit.
One last thing
The part unmarried co-owners underestimate is how differently the STR loophole can play out between two people who each expect the same result. If one co-owner runs the guest communication and cleaning schedule while the other is fully passive, only the active co-owner clears material participation in 2026, and only that person's share of the bonus depreciation offsets W-2 income directly. The passive co-owner still gets their percentage of the deduction, just carried forward against future passive income instead of used against a paycheck this year. That gap is worth discussing before the study is ordered, not after the return is filed.
