Most California real estate investors and business property owners assume they have to depreciate leasehold improvements over 15 or 39 years. That assumption is costing them tens of thousands of dollars per year in taxes they did not have to pay. The Section 179 deduction for leasehold improvements in 2025 California changes that math entirely — and with 100% bonus depreciation reinstated under the One Big Beautiful Bill Act (OBBBA), the opportunity to front-load write-offs has never been more powerful.

This is not a strategy for large REITs or institutional investors. It applies directly to California LLC owners, S Corp operators, and individual landlords who lease commercial space and spend money improving it. If you spent $50,000, $80,000, or more on qualified improvements to a leased property this year, you may be able to write off the entire amount in year one instead of spreading it across 15 years of slow deductions.

Here is exactly how it works, where the traps are, and how California’s non-conformity rules affect what you actually report to the FTB.

Quick Answer

For the 2025 tax year, Section 179 allows California business owners to immediately expense qualified leasehold improvements up to $1,160,000 federally (with a phase-out beginning at $2,890,000 in total asset purchases). When paired with 100% bonus depreciation — reinstated for assets placed in service after January 19, 2025 — business owners can often write off the full cost of eligible improvements in year one. California does not conform to 100% federal bonus depreciation, so state-level treatment differs. Understanding both layers is essential before filing.

What Qualifies as a Leasehold Improvement Under Section 179

A leasehold improvement is any permanent modification made to the interior of a commercial building that the tenant (or the landlord for a tenant) pays for. Think: new flooring, lighting upgrades, HVAC modifications, partition walls, plumbing rerouting, or specialized build-outs for a restaurant or medical practice.

Under the Tax Cuts and Jobs Act (TCJA) and confirmed under current law, these improvements now fall into a category called Qualified Improvement Property (QIP). QIP has a 15-year Modified Accelerated Cost Recovery System (MACRS) depreciation life at the federal level. That 15-year recovery period is what makes QIP eligible for both Section 179 expensing and 100% bonus depreciation.

What Does NOT Qualify

• Enlargements to the building’s footprint (adding square footage)
• Elevators or escalators
• Improvements to the structural components of the building (roof, load-bearing walls)
• Improvements attributable to the internal structural framework

The IRS is specific about this. Work done on the building’s exterior shell, structural integrity, or vertical transport systems is excluded from QIP classification. However, most interior tenant improvement work — the stuff that makes a space functional for a business — qualifies.

For a comprehensive breakdown of California-specific strategies related to property improvements, see our California Business Owner Tax Strategy Hub for deeper context on entity-level considerations that affect how these deductions flow through to your return.

The Section 179 + Bonus Depreciation Stack for 2025

As of the 2025 tax year, IRS Publication 946 governs how taxpayers elect Section 179 and apply depreciation rules. Here is the key hierarchy California business owners need to understand:

Step 1: Apply Section 179 First

The IRS requires you to apply Section 179 before bonus depreciation. For 2025, the federal Section 179 deduction limit is $1,160,000. This deduction is limited to your taxable income from active business activities — you cannot use Section 179 to generate a net operating loss (NOL).

Step 2: Apply 100% Bonus Depreciation to the Remainder

After Section 179 reduces the cost basis, 100% bonus depreciation under OBBBA applies to qualifying property placed in service after January 19, 2025. Unlike Section 179, bonus depreciation CAN create an NOL, which can be carried back or forward. For real estate investors, this opens the door to significant tax refunds in certain situations.

The Stacking Math

Here is what this looks like in practice for a California commercial tenant:

• Interior build-out cost: $120,000
• Section 179 election: $120,000 (subject to taxable income limit)
• Federal taxable income deduction: Full $120,000 in year one
• If Section 179 is limited by income: Remaining balance eligible for 100% bonus depreciation
• Net federal tax savings at 32% bracket: approximately $38,400 in year one

Without this stacking strategy, the same $120,000 deducted over 15 years at standard MACRS rates would only generate about $5,700 in first-year deductions. That is a $32,700 difference in year-one tax relief — from the same money spent.

Many real estate investors overlook this strategy entirely because they assume it only applies to equipment purchases. Qualified Improvement Property changes that assumption completely.

California Non-Conformity: The Trap That Catches Most Investors

Here is where California diverges sharply from federal law — and where most investors get surprised at tax time.

California does NOT conform to federal bonus depreciation rules under IRC Section 168(k). This is one of the most significant state-level non-conformity traps in California tax law, and it applies regardless of whether you file as an individual, LLC, S Corp, or partnership.

What California Does Allow

• California Section 179: California conforms to the federal Section 179 deduction, but with a lower limit. For 2025, California’s Section 179 limit is $25,000, compared to the federal $1,160,000.
• Standard MACRS Depreciation: The remaining cost basis must be depreciated over 15 years for QIP on your California return (Schedule CA), even if you took it all federally in year one.
• No Bonus Depreciation: California has not adopted 100% bonus depreciation. You must add back any federal bonus depreciation claimed when computing your California taxable income.

The Addback Requirement

When you file your California Form 540 or Schedule CA (540), you must add back the federal bonus depreciation deduction as income. Then California allows you to amortize that addback over the remaining MACRS life of the asset. The result is a temporary timing difference — you get the federal deduction now, but California defers it.

For a business with $120,000 in leasehold improvements, this creates a California state tax difference of approximately $8,000 to $10,000 in year one depending on your effective California rate. Plan for this by setting aside a portion of your federal tax savings to cover the California shortfall.

Our real estate tax preparation services specifically address this state-federal reconciliation issue, which is one of the most common errors we see in landlord and investor returns filed without professional guidance.

KDA Case Study: Commercial Tenant in San Diego Captures $74,000 in Year-One Deductions

A San Diego-based physical therapy practice operating as an S Corp signed a 7-year lease on a 3,500 square foot commercial space in early 2025. To make the space functional, they invested $185,000 in interior improvements: specialized treatment room walls, HVAC modifications, accessible entryways, and custom flooring throughout.

Their previous accountant had planned to depreciate the improvements over 15 years using standard MACRS, which would have generated $12,333 per year in deductions. Over seven years of the lease, they would have captured only $86,333 in total deductions before potentially abandoning the remaining basis.

KDA reclassified the improvements as Qualified Improvement Property and structured a Section 179 election plus 100% bonus depreciation stack:

• Section 179 elected: $85,000 (limited to S Corp taxable income for the year)
• Bonus depreciation applied to remainder: $100,000
• Total federal year-one deduction: $185,000
• Federal tax savings at 32% bracket: $59,200
• California addback managed and deferred over 14 years
• Net first-year benefit after California reconciliation: $47,800

KDA’s fee for the year: $4,200. First-year ROI: 11.4x. Over the 7-year lease, the accelerated deduction strategy generates an estimated $21,000 in additional after-tax cash flow compared to straight-line MACRS, even accounting for California’s deferral.

The practice owner used that first-year cash savings to fund a Solo 401(k) contribution, which generated an additional $7,200 in federal tax savings — a compounding effect of strategic planning.

Ready to see how we can help you? Explore more success stories on our case studies page to discover proven strategies that have saved our clients thousands in taxes.

Common Mistakes That Destroy Leasehold Improvement Deductions

This strategy is powerful, but it is easy to misapply. Here are the most expensive errors we see California investors and business owners make:

Mistake 1: Treating All Construction Costs as QIP

Not every dollar you spend on a commercial build-out qualifies as Qualified Improvement Property. Structural work, exterior modifications, and additions to the building do not qualify. If your contractor invoices a single lump sum, you may need a cost segregation study or a detailed cost allocation to separate qualifying interior work from non-qualifying structural work. Filing without this separation risks an IRS challenge and potential denial of the entire deduction.

Mistake 2: Ignoring the Taxable Income Limitation on Section 179

Section 179 is capped by your net income from active business activities. If your S Corp or LLC had a rough year and shows net income of $40,000, you cannot take more than $40,000 in Section 179 — even if your eligible improvements totaled $200,000. The solution is to elect Section 179 up to your income limit and then use bonus depreciation for the remaining balance, which can generate an NOL.

Mistake 3: Failing to File Form 4562

IRS Form 4562 is the depreciation and amortization form where all Section 179 elections and bonus depreciation claims are reported. Many self-prepared returns either omit this form entirely or complete it incorrectly. A missing or incorrect Form 4562 can trigger IRS processing errors or outright disallowance of the deduction.

Mistake 4: Not Claiming Abandonment Loss When You Vacate Early

If you vacate a leased space before the end of the asset’s depreciable life and the improvements are left behind, you may be able to claim an abandonment loss for the remaining un-depreciated basis. Most investors and tenants never claim this loss because their accountant does not flag it. On $100,000 of improvements with 8 years remaining on a 15-year schedule, the abandonment loss could be worth $40,000+ in additional deductions.

Mistake 5: Miscalculating the California Addback

California’s treatment requires a manual addback on Schedule CA. If your return preparer uses software that auto-flows federal figures to California without a QIP/bonus depreciation adjustment, you will understate your California taxable income. This creates an underpayment that can trigger FTB notices, interest, and penalties. The California underpayment penalty is 5% of the amount owed plus 0.5% per month.

Want to know how your overall property income is taxed in California? Run a quick estimate using this capital gains tax calculator to understand your exposure before you file.

Who Should Prioritize This Strategy Right Now

The Section 179 and bonus depreciation strategy for leasehold improvements is most valuable for:

• Business owners who lease commercial space and invest in build-outs: Medical offices, dental practices, restaurants, retail operators, and professional services firms that customized their leased space in 2025.
• Real estate investors who own commercial property and fund tenant improvements: Landlords who pay for tenant improvement allowances (TI allowances) can potentially treat those costs as QIP if structured correctly in the lease.
• S Corp and LLC owners with active business income: The Section 179 deduction requires active income. Pass-through entities that show consistent profitability can absorb large Section 179 deductions efficiently.
• California taxpayers with high state income: The California non-conformity creates a planning gap, but the federal savings are real and immediate. A taxpayer in the 32% federal bracket and 13.3% California bracket can still come out well ahead even after accounting for the California timing difference.

What If I Am a Landlord Who Paid for Tenant Improvements?

This is a nuanced area. If you are the building owner and you funded improvements to attract or retain a tenant, those improvements may or may not qualify as QIP depending on the structure of the arrangement. Improvements made by the landlord for a tenant’s use are generally treated as the landlord’s depreciable property — and if they qualify as interior improvements under the QIP definition, they may be eligible for the same accelerated treatment. Work with a tax advisor to document the lease structure and ownership of the improvements correctly before filing.

Documentation You Need Before You File

The IRS and FTB both require solid documentation to support accelerated depreciation claims. Before your return is prepared, gather:

• Signed lease agreement confirming you have leasehold interest in the improved space
• Contractor invoices and itemized bid breakdowns showing which work is interior vs. structural
• Certificate of occupancy or improvement completion date to confirm “placed in service” date
• Cost segregation study (recommended for improvements over $75,000)
• Completed Form 4562 with Section 179 election and bonus depreciation properly calculated
• California Schedule CA addback calculation reconciling federal and state depreciation

The placed-in-service date matters significantly. Improvements must be placed in service during the 2025 tax year to qualify for 2025 deductions. Planning an improvement project for Q4 2025? Make sure construction is complete and the space is actually usable before December 31st.

What Changes Under the One Big Beautiful Bill Act

The OBBBA reinstated 100% bonus depreciation for qualifying assets placed in service after January 19, 2025. This reversal of the TCJA’s phased reduction schedule (which had dropped bonus depreciation to 40% in 2025 under prior law) is one of the most significant tax changes for commercial real estate operators and business property tenants in years.

Key OBBBA points for California real estate investors:

• 100% bonus depreciation applies federally to QIP placed in service after January 19, 2025
• California still does not conform — the state addback requirement remains unchanged
• The Section 179 limit remains at $1,160,000 federally for 2025 (subject to inflation adjustments)
• The Section 179 phase-out begins at $2,890,000 in total qualifying property placed in service during the year
• California’s conformity to Section 179 remains capped at $25,000 for state purposes

This information is current as of March 20, 2026. Tax laws change frequently. Verify updates with the IRS or FTB if reading this later.

Frequently Asked Questions

Can I Use Section 179 on Leasehold Improvements If My Business Showed a Loss?

No. Section 179 is limited to your net income from active business activities. If your business reported a net loss for 2025, you cannot take the Section 179 deduction. You can, however, use bonus depreciation, which is not subject to the income limitation and can create or increase a net operating loss.

Do Leasehold Improvements Qualify for Section 179 in California?

California conforms to the federal Section 179 election for leasehold improvements that qualify as QIP. However, California’s deduction limit is $25,000 — not the federal $1,160,000. Any amount you deduct federally above $25,000 must be added back to your California taxable income and amortized over the remaining MACRS recovery period.

What Happens to Un-Depreciated Leasehold Improvements When I Leave the Property?

If you vacate the property and the improvements are permanently abandoned, you may be able to claim an abandonment loss deduction for the remaining book value of the improvements under IRC Section 165. This requires proper documentation including written evidence that the improvements were abandoned and have no salvage value. Consult a tax professional before claiming this loss.

Is a Cost Segregation Study Worth It for Leasehold Improvements?

For improvements under $50,000, a full engineering-based cost segregation study may cost more than it saves. For improvements over $75,000, it is almost always worth commissioning. The study identifies which components qualify for 5-year, 7-year, or 15-year classification vs. 39-year treatment, and provides the IRS-defensible documentation needed to support accelerated deductions during an audit.

Key Takeaway: The Section 179 deduction for leasehold improvements is one of the highest-leverage, most underutilized strategies available to California commercial tenants and property investors. When paired with 100% bonus depreciation under OBBBA, it can turn a $120,000 build-out into an $80,000+ year-one federal tax write-off — but only if the improvement is properly classified and the California non-conformity addback is accurately calculated.

“The IRS reinstated 100% bonus depreciation. California didn’t follow. That gap is where most California investors leave their biggest deductions on the table.”

Claim Your Leasehold Improvement Deductions Before They Expire

If you spent money improving a leased commercial space in 2025 and your accountant has not mentioned Qualified Improvement Property, Section 179, or bonus depreciation, you are almost certainly leaving real money behind. The window to claim these deductions on your 2025 return is open right now. Book a strategy session with our team before your return is filed. We will review your improvement costs, classify them correctly, stack the available deductions, and make sure your California addback is calculated so there are no FTB surprises later. Click here to book your consultation now.