Cost Segregation and Bonus Depreciation for San Diego Rental Property (2026)

San Diego investors are used to hearing that the market's real return is appreciation, not cash flow, and the numbers back that up: multifamily cap rates here are running 4.3 to 4.7 percent against a 6.1 percent national average, at an average price per unit around $398,500. What doesn't get talked about nearly as often is the tax lever that can meaningfully improve that thin cash flow in the near term without touching the property itself. Cost segregation paired with 100 percent bonus depreciation, now permanent under the 2025 tax law, lets an investor front-load a huge share of a property's depreciation into year one rather than spreading it evenly over 27.5 years. It's not a loophole and it doesn't create extra deductions out of thin air, but it changes when you get to use them, and for a lot of San Diego owners that timing shift is worth real money right now.

What cost segregation actually does

Standard residential rental depreciation treats the entire building as one asset, written off in equal amounts over 27.5 years under IRS rules. A cost segregation study breaks that same building into its individual components, engineering-based analysis that identifies which parts of the property actually wear out on a shorter timeline, appliances, carpeting, certain cabinetry and fixtures, and land improvements like landscaping, fencing, and paving, and reclassifies them into 5-year, 7-year, and 15-year recovery periods instead of the standard 27.5. It's worth being precise about what this does and doesn't accomplish: a cost segregation study doesn't increase the total amount of depreciation you'll ever claim on the property. It changes the schedule, pulling deductions that would otherwise trickle out over decades into the first few years of ownership instead.

A qualified study typically costs $2,500 to $20,000 depending on the property's size and complexity, with a lot of single-family rentals landing in the $2,500 to $4,500 range and some simplified desktop studies available for under $2,000. That cost is worth weighing against what the study actually finds, since a well-documented, engineering-based report is also what protects the deduction if the IRS asks questions later.

Why bonus depreciation makes this dramatically more powerful right now

Cost segregation has been available for decades, but it got significantly more valuable with the 2025 tax law. Under the One Big Beautiful Bill Act, 100 percent bonus depreciation was restored and made permanent, with no scheduled phase-down, for qualifying property placed in service after January 19, 2025. That matters because it means every asset a cost segregation study reclassifies into the 5-year, 7-year, or 15-year buckets, tangible property with a class life of 20 years or less, can be fully expensed in the year the property is placed in service rather than depreciated gradually even within its shorter recovery period. Combine the two strategies and a meaningful share of a rental property's total value, often somewhere in the neighborhood of 20 to 30 percent depending on the property type, can be written off entirely in year one, all while the building structure itself continues depreciating on its normal 27.5-year schedule.

For a San Diego investor sitting on a property purchased anywhere near current price levels, that first-year deduction can be substantial, and it's exactly the kind of near-term tax benefit that partially offsets the thin cash-on-cash returns the county's low cap rates otherwise produce.

The catch: passive losses don't just offset anything you want

This is where a lot of investors get tripped up, because a large depreciation deduction is only useful if you can actually use it against your income. Rental real estate is treated as a passive activity under IRS rules by default, and passive losses generally can only offset passive income, not the W-2 salary or active business income most investors are also earning. There's a narrow exception: the $25,000 special allowance under Section 469(i), available to investors who actively participate in managing the property, but it phases out between $100,000 and $150,000 of modified adjusted gross income and disappears entirely above that range, which rules it out for a lot of higher-earning San Diego investors precisely when a large cost segregation deduction would be most useful.

The full workaround is real estate professional status, which requires spending more than 750 hours a year in real property trades or businesses and more than half of your total working hours in those activities, a bar that effectively requires real estate to be your primary occupation rather than a side investment. For investors who don't clear that bar, there's also a cap to be aware of regardless: for 2026, Section 461(l) limits aggregate business losses a non-corporate taxpayer can deduct against other income to $256,000 for a single filer or $512,000 for a joint return, with anything beyond that carried forward rather than lost outright.

The short-term rental exception that changes the math for a lot of San Diego owners

There's a specific carve-out that matters a lot in a market where short-term rental investing is already common: an owner doesn't need real estate professional status at all if the property's average guest stay is seven days or less and the owner materially participates in operating it. Material participation is generally established by clearing one of a handful of specific hour thresholds, spending more than 500 hours a year on the activity, more than 100 hours with no one else spending more time on it, or more hours than everyone else involved combined. Meeting that test reclassifies the activity as a trade or business rather than a passive rental, which means the losses generated by a large cost segregation deduction can offset W-2 or other active income directly, without needing to qualify as a real estate professional in the first place.

This is worth reading alongside San Diego's short-term rental licensing rules specifically, since a property has to actually operate as a genuine short-term rental to qualify, both for this tax treatment and for the city's Tier 3 STR license in the first place. A property purchased with a cost segregation and short-term rental strategy in mind needs the licensing piece to actually pencil before the tax strategy is worth much at all.

What happens to the deduction when you sell

Front-loading depreciation doesn't make the underlying tax liability disappear, it defers it, and the recapture rules differ depending on which bucket of assets you're talking about. The portion of gain attributable to the building structure's standard depreciation is taxed as unrecaptured Section 1250 gain at a flat 25 percent federal rate when you sell, the same rule that applies to any rental property regardless of whether you did a cost segregation study. The personal property components a cost segregation study reclassified into 5-, 7-, or 15-year buckets are treated differently: depreciation on those assets is generally recaptured as ordinary income under Section 1245, up to the amount you deducted, when you sell or dispose of them. For an investor in a high tax bracket, that ordinary income treatment on the accelerated portion can be a meaningfully worse outcome at sale than the flat 25 percent rate on the building itself, which is worth running through your accountant before you assume the entire benefit is a permanent win rather than a very favorable timing shift.

The wrinkle that matters if you're planning a future 1031 exchange

This is a coordination point that's easy to miss, and it connects directly to how 1031 exchanges work. Since the 2017 Tax Cuts and Jobs Act, only real property qualifies for like-kind exchange treatment, personal property exchanges were eliminated entirely. A cost segregation study, by design, reclassifies a meaningful share of a property's value into personal property categories for depreciation purposes. If you later try to 1031 exchange that same property, the personal property components a cost segregation study identified generally aren't eligible for like-kind treatment the way the real property portion is, which can trigger gain recognition on those specific components even while the real property gain defers normally. If cost segregation and a future exchange are both part of your plan for the same property, loop your CPA and your qualified intermediary in together well before you list it, since this is exactly the kind of detail that's expensive to discover after closing rather than before.

What this means if you're buying rental property in San Diego right now

Given how thin cap rates are running countywide, a cost segregation study is worth pricing into your underwriting from the start rather than treating it as an afterthought once you already own the property, since the near-term tax benefit is one of the more reliable ways to improve first-year cash flow in a market like this one. If a short-term rental strategy is part of your plan, confirm both the STR licensing math and your material participation hours line up before counting on the non-passive tax treatment, since one without the other leaves you with a compliant rental but a passive loss you can't use.

What this means if you already own rental property here

A cost segregation study isn't limited to the year you buy. It can generally be done on a property you've owned for years through what's called a look-back study, catching up the accelerated depreciation you missed in prior years through a single adjustment rather than amending old returns. If you're carrying a rental property with real appreciation and thin cash flow, the same profile driving a lot of San Diego owners toward out-of-state 1031 exchanges, it's worth running the numbers on a cost segregation study before you decide whether selling or holding makes more sense this year.

Getting your specific numbers right

Whether cost segregation and bonus depreciation actually move the needle for you depends on your income level, whether you qualify as a real estate professional or under the short-term rental exception, and how the timing lines up with any exchange you're planning. This isn't a substitute for advice from a CPA who can run your specific numbers, but if you're weighing whether a cost segregation study makes sense on a property you own or one you're evaluating, reach out and we'll go through the real numbers together before you commit to the study.