Section 179 vs Bonus Depreciation Difference (2026)

Both provisions deduct the full cost of qualifying property in the year it is placed in service. With 100% bonus depreciation restored permanently, many owners assume the choice no longer matters.

It matters more than ever, because the differences are now entirely about control rather than about rate. Four distinctions decide which one you want.

Difference One: Section 179 Cannot Create a Loss

IRC Sec. 179(b)(3) limits the deduction to the taxpayer's aggregate taxable income from the active conduct of any trade or business. Any excess carries forward.

Bonus depreciation under IRC Sec. 168(k) has no such limit. It can drive taxable income negative, creating a net operating loss.

For a profitable business, this rarely binds. For a startup, a business having a down year, or a real estate investor with limited active business income, it binds constantly.

The carryforward is not lost, but it is deferred, and the taxpayer who wanted a current deduction does not get one.

Difference Two: Section 179 Is Elected Asset by Asset

You choose which specific assets receive Sec. 179 treatment and how much of each asset's cost to expense. You can take $40,000 on a $95,000 machine and depreciate the rest normally.

Bonus depreciation applies automatically to all qualifying property in a class unless you elect out, and the election out applies to the entire class for that year. You cannot bonus one five-year asset and not another.

This makes Sec. 179 the precision instrument. A business owner who wants taxable income to land at a specific number, perhaps to stay under a qualified business income threshold, to preserve a credit, or to manage a state tax result, uses Sec. 179 to hit the target.

Difference Three: The Dollar Caps

Sec. 179 has a dollar limit and a phase-out. For 2025 the deduction limit is $2,500,000, reduced dollar for dollar once qualifying property placed in service exceeds $4,000,000. These amounts are indexed annually.

Bonus depreciation has no dollar cap at all. A taxpayer placing $18,000,000 of qualifying property in service deducts all of it.

For most owners the Sec. 179 cap is irrelevant. For a large contractor, a manufacturer, or a real estate investor running multiple cost segregation studies in a year, bonus is the only provision that can absorb the volume.

Difference Four: What Property Qualifies

Sec. 179 reaches some property bonus depreciation does not. Under IRC Sec. 179(f), qualified real property includes roofs, HVAC, fire protection and alarm systems, and security systems installed on nonresidential real property after the building was placed in service.

That is meaningful. A $180,000 roof replacement on a commercial building is 39-year property, not bonus eligible, but can be expensed under Sec. 179.

Sec. 179 also applies to certain property used in furnishing lodging, which was formerly excluded.

Bonus depreciation reaches property Sec. 179 does not in one important respect. Sec. 179 requires property used in the active conduct of a trade or business. Property used in a passive rental activity generally does not qualify. Bonus depreciation has no such requirement, which is why cost segregation studies on rental real estate rely on bonus rather than Sec. 179.

State Conformity Is the Quiet Factor

Many states decouple from federal bonus depreciation while conforming to Sec. 179, often at a lower cap.

Pennsylvania, New Jersey, California, and several others require add-backs of federal bonus depreciation, recomputing state depreciation on a different schedule. That creates a permanent difference in timing and ongoing compliance complexity.

Where a state conforms to Sec. 179 but not bonus, electing Sec. 179 can produce a matching state deduction that bonus depreciation would not. For a business operating primarily in one such state, this can flip the analysis entirely.

The state analysis should be run alongside the federal one rather than after.

The Ordering Rule

Where both apply, Sec. 179 is taken first, then bonus depreciation on the remaining basis, then regular MACRS depreciation on whatever remains.

This ordering is useful. A taxpayer can elect Sec. 179 on a specific asset to capture a state benefit, then let bonus handle the rest of the class federally.

Worked Example: Two Owners, Different Answers

A contractor has $840,000 of business income and buys $620,000 of equipment. Either provision fully deducts it. The contractor operates in Pennsylvania, which disallows bonus depreciation but conforms to Sec. 179 at the federal limit. Electing Sec. 179 produces a matching state deduction worth roughly $19,000 that bonus would not. Sec. 179 wins.

A real estate investor buys a $2,400,000 apartment building and runs a cost segregation study identifying $610,000 of five-year and 15-year property. Sec. 179 is largely unavailable, because rental real estate is generally not an active trade or business for this purpose. Bonus depreciation is the only route, and it produces the full $610,000 deduction.

A startup manufacturer has $180,000 of business income and places $740,000 of equipment in service. Sec. 179 is capped at $180,000 by the taxable income limit, with the rest carrying forward. Bonus depreciation deducts the entire $740,000, creating a net operating loss the owner can carry forward under IRC Sec. 172. Bonus wins.

A medical practice owner with $960,000 of income wants taxable income to land at $394,000 to manage a specific threshold. Sec. 179 lets them elect exactly $566,000 across selected assets. Bonus would take everything in the class. Sec. 179 wins.

Frequently Asked Questions

Which is better, Section 179 or bonus depreciation?

Neither is universally better. Bonus depreciation has no dollar cap and can create a loss, making it right for large purchases and for rental real estate. Sec. 179 gives asset-by-asset control and often produces a state deduction where bonus does not.

Can Section 179 create a net operating loss?

No. IRC Sec. 179(b)(3) limits the deduction to aggregate taxable income from the active conduct of a trade or business, with the excess carrying forward. Bonus depreciation has no such limit and can drive taxable income negative.

Can I use Section 179 on rental property?

Generally not for the personal property components identified in a cost segregation study, because Sec. 179 requires active conduct of a trade or business and most rental activity does not qualify. This is why cost segregation studies rely on bonus depreciation.

Can I expense a new commercial roof?

Under Sec. 179, yes. Qualified real property under IRC Sec. 179(f) includes roofs, HVAC, fire protection, alarm, and security systems installed on nonresidential real property after it was placed in service. Bonus depreciation does not reach these, since they are 39-year property.

Do states treat them the same way?

Often not. Many states disallow federal bonus depreciation and require an add-back while conforming to Sec. 179, sometimes at a lower cap. Pennsylvania, New Jersey, and California are common examples. Run the state analysis alongside the federal one.

Section 179 vs Bonus Depreciation: Which One Should You Use?