Bottom Line
- Section 179 and bonus depreciation both allow accelerated write-offs, but they have different rules, different limitations, and different applications for real estate
- Most cost segregation benefits come from bonus depreciation under IRC §168(k), not Section 179
- Section 179 is capped at $1,220,000 (2025) and limited to taxable income; bonus depreciation has no cap and can create a net loss
- They are not mutually exclusive — both can apply in the same tax year
Section 179 and bonus depreciation both allow accelerated write-offs, but they have different rules, different limitations, and different applications for real estate investors. Most cost segregation benefits come from bonus depreciation under IRC §168(k), not Section 179. Understanding the distinction matters because it affects how much you can deduct, when you can deduct it, and whether the deduction can create a tax loss.
This confusion shows up constantly. Investors ask their CPAs about "Section 179-ing" a rental property when what they actually mean is bonus depreciation on reclassified components. The two provisions overlap in some areas but differ in ways that materially affect your tax return. Here’s how they compare, when each applies, and how they interact with cost segregation.
Side-by-Side Comparison
The table below covers the six areas where Section 179 and bonus depreciation diverge most for real estate investors. The differences in annual limits and income requirements are the ones that matter most in practice.
| Feature | Section 179 | Bonus Depreciation |
|---|---|---|
| Annual limit | $1,220,000 (2025) | No limit |
| Real property eligible? | Limited — roofs, HVAC, fire protection, security systems | All tangible property with ≤20-year MACRS recovery |
| Buildings / structures | Not eligible | Not eligible (but components are, via cost seg) |
| Must be profitable? | Yes — limited to taxable income | No — can create a net loss |
| Recapture | Ordinary income | Ordinary income (25% rate for real property under §1250) |
| Phase-out threshold | Begins at $3,050,000 in total asset purchases | No phase-out |
The key takeaway: bonus depreciation is broader, uncapped, and more flexible. Section 179 is a narrower tool with specific guardrails. For real estate investors running a cost segregation study, virtually all of the Year 1 acceleration comes from bonus depreciation, not Section 179. For a deeper look at how bonus depreciation works in 2025–2026, see our dedicated guide.
How They Work with Cost Segregation
A cost segregation study doesn’t change which tax provision you use. It changes which components are eligible for accelerated treatment in the first place.
Without a cost seg study, your entire building (minus land) sits on the default depreciation schedule: 27.5 years for residential rental property or 39 years for commercial. That means roughly 3.6% or 2.6% of the building’s cost is deducted each year. No acceleration is available because the IRS treats the building as a single asset.
A cost segregation study breaks the building into its individual components — flooring, cabinetry, appliances, light fixtures, landscaping, driveways, specialty electrical — and classifies each one into its correct MACRS recovery period. Cabinetry is 5-year property. Landscaping is 15-year property. And so on, component by component, following the classification rules in Rev. Proc. 87-56 and the IRS Cost Segregation Audit Techniques Guide.
Once those components are reclassified into 5-year, 7-year, or 15-year categories, they become eligible for 100% bonus depreciation under IRC §168(k). That’s the mechanism: cost seg identifies the components, bonus depreciation deducts them in Year 1.
Section 179 applies to a narrower set of real property improvements. For most investors, bonus depreciation does the heavy lifting — typically 90%+ of the accelerated deduction from a cost segregation study comes through §168(k), not §179.
To understand how much acceleration is typical for different property types, see our cost segregation benchmarks or read about the difference between cost seg and standard depreciation.
When Section 179 Matters for Real Estate
Section 179 isn’t irrelevant to real estate — it just applies in specific scenarios that are different from the broad component reclassification that cost segregation enables. Here are the situations where Section 179 is the right tool.
- Qualified Improvement Property (QIP) — Interior improvements to an existing commercial building (not an expansion, not new construction). Think tenant buildouts, renovated lobbies, or reconfigured office layouts. QIP is 15-year property that qualifies for both Section 179 and bonus depreciation, giving you flexibility in how you deduct it.
- Specific building systems — Roofs, HVAC, fire protection and alarm systems, and security systems placed in service after the building was originally put in service. These are the only structural-adjacent items Congress specifically made Section 179–eligible for real property.
- Renovation projects — When you’re adding or replacing building systems (a new roof, a new HVAC system, a fire suppression upgrade), Section 179 lets you expense the cost in the year placed in service rather than depreciating it over 39 years. This is particularly useful for commercial landlords making capital improvements between tenants.
- Income-limited situations — Because Section 179 cannot create a net loss, some investors use it strategically to reduce taxable income to zero without generating a loss that might attract scrutiny or create passive activity complications. Bonus depreciation, by contrast, can create losses that carry forward.
The practical distinction: Section 179 is a targeted provision for specific capital improvements you make to an existing building. Bonus depreciation, applied through a cost segregation study, is a broad provision that accelerates depreciation on components that were already part of the building when you bought it. Different tools for different jobs.
Current Status: 2025–2026
The One Big Beautiful Bill Act (signed July 2025) permanently restored 100% bonus depreciation for property placed in service in 2025 and beyond. This reversed the phase-down that had reduced bonus depreciation to 80% in 2023 and 60% in 2024.
Section 179 limits adjust annually for inflation. The 2025 deduction limit is $1,220,000, with the phase-out beginning at $3,050,000 in total qualifying property purchases.
Both provisions are available simultaneously. They are not mutually exclusive. An investor could use Section 179 for a new HVAC system installed during a renovation and bonus depreciation on components identified through a cost segregation study on the same property in the same tax year. Your CPA determines the most advantageous combination based on your specific tax situation.
Frequently Asked Questions
Section 179 applies to rental real property only for specific building improvements: roofs, HVAC systems, fire protection, alarm and security systems, and certain interior renovations classified as Qualified Improvement Property. It does not apply to the building structure itself or to residential rental property components reclassified through cost segregation. For most rental property investors, bonus depreciation under IRC §168(k) — applied to components identified in a cost segregation study — provides a larger and more flexible deduction.
Both allow you to deduct property costs faster than standard depreciation, but they differ in key ways. Section 179 has an annual dollar limit ($1,220,000 for 2025), can only be used against taxable income (it cannot create a net loss), and applies to a narrow set of real property improvements. Bonus depreciation under IRC §168(k) has no dollar limit, can create a net loss, and applies to all tangible property with a MACRS recovery period of 20 years or less — which includes every component reclassified through a cost segregation study.
You need a cost segregation study to claim bonus depreciation on building components. Without one, the entire building (minus land) is depreciated over 27.5 years (residential) or 39 years (commercial) as a single asset. A cost segregation study identifies and reclassifies individual components — flooring, cabinetry, landscaping, specialty electrical, site improvements — into shorter MACRS recovery periods (5, 7, or 15 years). Those reclassified components then qualify for 100% bonus depreciation in Year 1. The study itself is what creates the eligibility.
Related Reading
Bonus Depreciation in 2025–2026: What Real Estate Investors Need to Know
100% bonus depreciation is back permanently. Here's what changed and how it affects cost segregation.
Cost Segregation vs Standard Depreciation
The mechanics of how cost seg accelerates depreciation compared to the default 27.5 or 39-year schedule.
Cost Segregation Benchmarks by Property Type
Typical reclassification rates and tax savings ranges across residential and commercial property types.