A $200,000 cost-seg loss is worthless this year if the passive activity rules trap it. Here’s how to know — before you pay for a study — whether your deduction is usable.
By Foad Nabi, EA · Enrolled Agent · California · June 2026
This is the question that should come before you pay for a cost segregation study, and it’s the one most people skip: even if the study produces a $200,000 first-year deduction, can you actually use it this year? For most rental owners, the honest answer is “not against your salary” — because of the passive activity loss rules. Understanding those rules is what separates a deduction that cuts your tax bill now from one that sits on a shelf for years.
Under Section 469, rental real estate is presumed “passive,” no matter how involved you are. Passive losses can only offset passive income — other rentals, certain investments — not your wages or active business profit. So a large cost-seg loss on a long-term rental usually can’t touch a doctor’s W-2 or a business owner’s Schedule C income. It carries forward until you have passive income or sell the property. Not lost — just deferred, sometimes for a long time.
There’s a small exception: if your modified AGI is under $100,000 and you “actively participate,” you can deduct up to $25,000 of rental losses against ordinary income, phasing out completely by $150,000 of AGI. Most people doing cost segregation earn too much to use it.
1. Real estate professional status (REPS). If you (or your spouse) spend more than 750 hours and more than half your total working time in real property trades or businesses, and you materially participate in your rentals, your rental losses become non-passive — usable against any income. This is gold for full-time investors and for couples where one spouse works real estate full-time while the other earns a high W-2. The hours are real, they must be logged, and “I own some rentals on the side” does not qualify if you also work a 40-hour job elsewhere.
2. The short-term rental route. A rental with an average stay of seven days or fewer isn’t a “rental activity” under the rules at all, so material participation alone (no REPS required) makes the loss non-passive. This is the more accessible path for high earners who can’t claim 750 real-estate hours. It has its own article on this site.
Decide whether the loss will be usable BEFORE you commission a study. A $200k deduction you can’t use this year is worth far less than the study fee implies. Usability first, study second.
Material participation has seven tests, but the ones that matter in practice: more than 500 hours in the activity; or 100+ hours and more than anyone else; or substantially all the work. Whatever the path, the IRS wants a contemporaneous log — dates, hours, what you did. This is the single most-litigated point in this area. Calendars, not memories.
The passive activity rules apply for California too, and largely mirror the federal ones — so REPS or short-term-rental treatment governs both. But remember the depreciation amounts differ: California disallows bonus depreciation, so even when your loss is fully usable, the California loss is smaller and spread over years. And California’s NOL suspension for high-income taxpayers through 2026 can temporarily trap a large state loss even when it’s non-passive. Usability and amount are two separate questions in this state, and both have to clear.
Cost segregation is only as valuable as your ability to use the deduction it creates. If you’re a passive investor earning a high salary with long-term rentals and no REPS or short-term-rental angle, a study still has value — but mostly as deferred deductions and a hedge against future passive income or sale, not an immediate tax cut. If you qualify as a real estate professional, or you self-manage a short-term rental, that same study can wipe out a huge chunk of this year’s tax. Same study, completely different value — and which one you’re in is knowable before you spend a dollar.
Foad is a federally licensed Enrolled Agent who writes about tax and bookkeeping for small businesses.