Here is the rule: take §179 first on assets bonus cannot reach, then bonus on everything else, then regular MACRS. The two provisions are not competitors. They cover different property, and which one you reach for depends on what you bought and how much taxable income you have.
The clearest case is a roof. A $180,000 roof on your nonresidential building is not bonus-eligible at all. It is §179-eligible. That single fact decides the analysis.
Key takeaways
- Bonus depreciation is 100% and permanent for qualified property acquired and placed in service after January 19, 2025, with no dollar cap.
- §179 for 2026 is capped at $2,560,000, phasing out from $4,090,000 of qualifying property and gone at $6,650,000.
- §179 cannot create a loss. It is limited to business taxable income, excess carried forward. Bonus can create a loss.
- §179 reaches roofs, HVAC, fire protection and security systems on nonresidential real property. Bonus never reaches the 39-year structure.
- The default order is §179 first, then bonus, then MACRS — flip it when the §179 cap is scarce or your state decouples.
The Head-to-Head Comparison
| Section 179 | Bonus depreciation, §168(k) | |
|---|---|---|
| 2026 dollar cap | $2,560,000 | None |
| Phase-out | Begins at $4,090,000; gone at $6,650,000 | None |
| Rate | Up to 100% of the elected amount | 100% after Jan 19, 2025 |
| Can it create a loss? | No; limited to business taxable income, excess carries forward | Yes, subject to §469 and §461(l) |
| Election granularity | Asset by asset, and you pick the amount | Class-wide, all or nothing |
| Roofs, HVAC, fire protection, security | Yes, on nonresidential real property under §179(f) | No |
| 5-, 7-, and 15-year property from a study | Yes | Yes |
| Qualified improvement property | Yes | Yes |
| Residential rental improvements | Generally unavailable | Available for qualifying 20-year-or-less property |
| State conformity | Widely, though not universally, conformed | Frequently decoupled |
Two rows carry most of the weight: the loss row and the §179(f) row.
Why the Taxable Income Limitation Is the Real Constraint
Section 179 is capped by your aggregate business taxable income. Elect more and the excess does not vanish, but it does not help you this year either. It carries forward.
Bonus has no such limit. A study on a newly acquired property routinely produces a deduction larger than the property's net income, and bonus lets that flow through as a loss. Whether the loss is usable is a separate question, governed by the passive activity rules of §469 and by the excess business loss limitation of §461(l), which OBBBA made permanent with 2026 thresholds of $256,000 single and $512,000 married filing jointly. Disallowed excess business loss becomes an NOL carryforward, and post-2017 NOLs offset only 80% of future taxable income. Read the excess business loss limitation before assuming a large deduction lands where you want it.
The mirror image, then: §179 is blocked by your income, and bonus by the character of the loss it creates.
What Section 179 Reaches That Bonus Cannot
This is the underrated half of the comparison. Bonus applies to property with a MACRS recovery period of 20 years or less, plus qualified improvement property. The 39-year structure sits permanently outside that boundary.
Section 179(f) opens a specific door. On nonresidential real property, you may elect §179 for roofs, heating, ventilation and air conditioning property, fire protection and alarm systems, and security systems.
These are structural components, and bonus will never touch them. For an owner replacing a roof or a rooftop HVAC package, §179 is the only route to an immediate write-off, which is why the ordering rule exists. See renovations and tenant improvements.
The Ordering Rule, and When to Flip It
The default sequence is mechanical and right most of the time:
- §179 on property bonus can't reach — roofs, HVAC, fire protection, security.
- Bonus on everything else — 5-, 7-, and 15-year property from your study, and QIP.
- Regular MACRS on the balance.
Modify it in three situations. Near the $4,090,000 phase-out, every dollar of qualifying property erodes the cap, so spend §179 only where bonus cannot substitute. If taxable income is thin, §179 is worth less this year than the election suggests. And if your state decouples from bonus but conforms to §179, reversing the order can produce a materially better state result; see state tax conformity.
Worked Example: A $180,000 Roof
Example: a $180,000 roof replacement on a nonresidential building, placed in service in March The owner also placed $420,000 of 5- and 15-year property in service from a cost segregation study the same year. Business taxable income before these deductions is $700,000. Combined marginal rate assumed at 35%.
| Asset | Cost | Bonus-eligible? | §179-eligible? | Election | Year-one deduction |
|---|---|---|---|---|---|
| Roof | $180,000 | No | Yes, §179(f) | §179 | $180,000 |
| 5-year property | $300,000 | Yes | Yes | Bonus | $300,000 |
| 15-year land improvements | $120,000 | Yes | Yes | Bonus | $120,000 |
| Total | $600,000 | $600,000 |
The roof is the point. Without a §179 election, $180,000 on a 39-year life yields roughly $3,700 in year one, because MACRS applies the mid-month convention to real property and a March placement carries a 2.033% first-year factor. Elected under §179, it yields $180,000, about $61,000 of deferred tax at 35%, and $700,000 of taxable income absorbs it with nothing carried forward.
Note what did not happen: §179 was not spent on the 5- and 15-year property, because bonus covers those with no cap and no income limit. Preserving the cap for the roof is the strategy. Your result depends on your tax rate and whether you can use passive losses.
Four Places Section 179 Runs Out
Residential rental property is largely out. The §179(f) categories apply to nonresidential real property. An apartment owner replacing a roof cannot elect §179 and cannot use bonus either. That roof depreciates over 27.5 years. It is one of the sharpest asymmetries in the rules, and it surprises multifamily owners every year.
The taxable income limit bites hard. An investor with a large portfolio and modest business taxable income may find the §179 election almost entirely deferred. The carryforward is genuine, but a deduction in 2031 is not a deduction in 2026, and time value is the whole reason to accelerate.
§179 requires active trade or business use. If qualifying business use later drops, part of the elected deduction can be recaptured. The election is a monitoring obligation, not just a filing decision.
Neither provision eliminates tax. Both defer it. Accelerated deductions on §1245 property return as ordinary-income recapture on sale, so the honest framing is time value plus rate arbitrage, not free money. For the full bonus landscape, including the transition elections under IRS Notice 2026-11, see the 2026 bonus depreciation guide.
Frequently Asked Questions
Can I use both §179 and bonus in the same year?
Yes, and most owners with a study should. Section 179 applies first to the assets you designate, and bonus then applies to the remaining eligible basis.
Which is better for a $60,000 HVAC unit on a commercial building?
Section 179, because bonus does not apply to a structural component of a 39-year building. If business taxable income supports the election, that $60,000 is deductible in year one under §179(f) rather than over 39 years.
Do states follow these rules?
Not uniformly. Many states conform to §179 with their own lower caps while decoupling from bonus entirely, so federal and state depreciation schedules diverge. Model both before choosing an election order.
See What Your Property Would Yield
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This article is provided by Precision Cost Segregation for general educational purposes and does not constitute tax, legal, or accounting advice. Tax outcomes depend on your specific facts, your tax rate, your passive activity position, and your entity structure. Figures shown are illustrative. Consult your CPA or tax advisor before acting, and engage a qualified professional to perform any cost segregation study. Information is current as of publication.
This article is general information, not tax or legal advice. Depreciation outcomes depend on your facts, elections, and current law — consult your CPA before acting. © 2026 Precision Cost Segregation.