Reduction in Basis: Section 179, Bonus Depreciation, and Credits

A reduction in basis for depreciation is the dollar-for-dollar shrinking of a business asset’s depreciable cost whenever you claim a tax benefit that already recovered part of that cost. The common triggers are Section 179 expensing, bonus depreciation, investment and energy tax credits, non-taxable rebates or subsidies, casualty loss deductions, and canceled debt you excluded from income. Each reduction lowers the figure that flows into your MACRS calculations, and each one comes back as ordinary income through recapture when you sell. Get the sequence wrong and the error compounds every year you own the asset.

What Depreciable Basis Actually Is

Your initial basis is what you paid to acquire the property and put it in service: purchase price, sales tax, freight, installation labor, and similar costs.¹ That total is the ceiling on everything you can ever recover through deductions tied to the asset.

Depreciable basis is the slice of that initial cost still eligible for MACRS recovery after every required reduction. The IRS lists the items that decrease basis, including Section 179 deductions, investment and energy credits, non-taxable subsidies, casualty and theft losses, and certain canceled debt.² The rationale for every reduction is the same: you cannot deduct a dollar you did not actually spend, or a dollar you already recovered through another tax benefit.

Section 179 Comes Off First

Section 179 lets you deduct the full cost of qualifying business property in the year you place it in service instead of spreading the cost across years of depreciation.³ Whatever amount you expense under Section 179 leaves your depreciable basis first, before any other adjustment.⁴

Buy $110,000 of qualifying equipment, elect $50,000 under Section 179, and your remaining depreciable basis is $60,000. That $60,000 is the only amount available for bonus depreciation or regular MACRS. The annual Section 179 deduction is capped at $2,500,000 and phases out dollar-for-dollar once total qualifying property placed in service during the year exceeds $4,000,000.³ Both thresholds are indexed for inflation, so confirm the current year’s figures before filing.

Bonus Depreciation Reduces What Section 179 Left

After Section 179, the special depreciation allowance (bonus depreciation) applies to the remaining basis. For qualifying property acquired and placed in service after January 19, 2025, businesses can deduct 100 percent of the remaining cost in the first year.⁵ The One Big Beautiful Bill Act made the 100 percent rate permanent, replacing the phase-down schedule that had otherwise dropped the rate to 40 percent for 2025.⁶

At 100 percent, bonus depreciation zeroes out the remaining basis in year one, leaving nothing for regular MACRS. You do not have to take it. If you expect higher rates in later years or cannot absorb a large first-year deduction, you can elect a reduced 40 percent allowance (60 percent for certain long-production-period property and aircraft).⁶ Whatever bonus amount you actually claim reduces basis before regular MACRS begins.⁷

Investment Credits: 100 Percent, With an Energy Exception

Claim an investment tax credit under Section 46 or a related provision and the general rule is a full dollar-for-dollar basis reduction.⁸ A $20,000 rehabilitation credit on a historic structure drops depreciable basis by $20,000. The trade-off is intentional: credits offset tax dollar-for-dollar, so the code claws back basis to prevent recovering the same cost twice.

Energy credits and clean electricity investment credits get more favorable treatment. Only 50 percent of the credit reduces basis.⁸ A $30,000 energy credit on a solar installation reduces basis by $15,000, and you depreciate the other $15,000 as though you had paid it in cash. Every other investment credit in that subpart, including the advanced manufacturing credit, the childcare facilities credit, and the rehabilitation credit, requires the full 100 percent reduction.

Rebates, Grants, and Subsidies

Money that someone else paid for the asset comes out of your basis. The IRS addressed this directly for home energy rebate programs under the Inflation Reduction Act: a rebate received at purchase reduces cost basis under Section 1012, and a rebate received later triggers a basis adjustment under Section 1016.⁹ Spend $10,000 on qualifying equipment, receive a $5,000 rebate at the register, and your basis is $5,000.

The same logic applies to state grants, utility incentives, and other non-taxable subsidies used to offset a purchase. Publication 551 lists exclusion of subsidies for energy conservation measures and rebates treated as adjustments to the sales price among items that decrease basis.² Timing determines whether the reduction hits the original cost or a later adjustment; the net result is the same.

Casualty Losses and Insurance

If business property is damaged, destroyed, or stolen and you claim a casualty or theft loss, basis decreases by the amount of the loss. Insurance reimbursements also reduce basis: subtract any proceeds you receive or expect to receive when computing the deductible loss.¹⁰ For property that is completely destroyed, the loss equals adjusted basis minus salvage value and insurance payments. If the payout exceeds adjusted basis, you have a gain and may owe tax on the difference unless you reinvest in replacement property.

Excluded Canceled Debt

Exclude canceled business debt from gross income under Section 108 (for example, because you were insolvent or in bankruptcy) and the code requires an offsetting reduction, one form of which is a cut to the basis of your depreciable property. The reduction takes effect on the first day of the tax year following the year of exclusion.¹¹

The regulations set a priority order: real property securing the discharged debt first, then personal property securing the debt, then remaining business or investment property.¹¹ Basis cannot go below zero on any asset. Taxpayers who elect under Section 108(b)(5) to apply the reduction specifically to depreciable property can do so, but only against property that actually qualifies as depreciable. The sequencing rules here are unforgiving, and professional help usually earns its cost.

The Allowed-or-Allowable Rule

Section 1016(a)(2) reduces basis by the depreciation “allowed as deductions” or, if greater, the amount “allowable” under the code.¹² “Allowable” means the depreciation you were entitled to claim, whether or not you actually claimed it.

The consequence lands at sale. Own a rental building for ten years and never claim a dollar of depreciation, and the IRS computes gain as if you had claimed it every year. Your basis is lower, your gain is higher, and you owe recapture tax on depreciation you never benefited from. Proving that the amount “allowed” was less than the amount “allowable” requires records that most taxpayers do not keep.¹³ Always claim the depreciation you are entitled to, because the IRS treats you as though you did.

The Sequence, With Numbers

The order of reductions is fixed by the Form 4562 instructions and Publication 946.⁴ Change the order and the numbers change with it.

Start With Full Cost

Add purchase price, sales tax, freight, installation, and other costs to acquire and place the property in service. A machine priced at $100,000, with $5,000 shipping and $5,000 installation, has an initial basis of $110,000.¹

Subtract Section 179

Expense $50,000 under Section 179 and basis drops to $60,000. This happens before bonus depreciation is calculated.⁷

Apply Bonus Depreciation

Bonus applies to the remaining $60,000. At 100 percent, you deduct the full $60,000 and nothing is left for regular MACRS. Elect the reduced 40 percent rate and you deduct $24,000, leaving $36,000 to recover over the class life through standard MACRS.

Reduce for Credits

Reduce basis by the required share of any investment or energy credit: 50 percent for energy and clean electricity credits, 100 percent for most other investment credits.⁸ In practice, you generally will not combine Section 179 with an investment credit on the same asset, so this step usually applies to property you chose to depreciate rather than expense.

Subtract Rebates and Subsidies

Remove any non-taxable rebates, grants, or subsidies that offset your purchase cost. A $5,000 utility rebate takes $5,000 off basis. What remains is the depreciable basis that enters your MACRS calculations.

Recapture at Sale

Every reduction you made comes back when you sell. Under Section 1245, gain on the sale of depreciable personal property is treated as ordinary income (up to 37 percent for individuals) to the extent of all depreciation and amortization adjustments previously allowed or allowable.¹³

The recapturable amount includes regular MACRS deductions, bonus depreciation, Section 179 deductions, and basis reductions from investment credits (net of any amount already recaptured when a credit was clawed back).¹⁴ Section 179 amounts are explicitly treated as amortization for recapture purposes, so expensing rather than depreciating does not avoid ordinary income treatment.¹³ Combined with the allowed-or-allowable rule, taxpayers who skipped depreciation for years can face five-figure recapture bills they did not see coming.

Where It All Gets Reported

Form 4562, Depreciation and Amortization, is the worksheet for these calculations. You enter initial cost, subtract the Section 179 election on the form, apply bonus depreciation to what remains, and carry the result into the MACRS lines.¹⁵ Credit-related basis reductions come out before the remaining basis enters the MACRS section.

Investment and energy credits themselves are reported separately on Form 3468, which feeds the general business credit forms.¹⁶ The basis reduction does not appear on Form 3468; you handle it by entering the reduced figure on Form 4562.

Keep purchase invoices, documentation of any rebates or grants, credit calculations, and a written computation showing each reduction in order. On audit, initial cost minus Section 179, minus bonus depreciation, minus credit-related reductions, minus subsidies should tie exactly to the figure on your MACRS lines. Any gap is the first thing an examiner will flag.

1
Internal Revenue Service. Depreciation Frequently Asked Questions
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Internal Revenue Service. Publication 551 – Basis of Assets
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Office of the Law Revision Counsel. 26 US Code 179 – Election to Expense Certain Depreciable Business Assets
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Internal Revenue Service. Instructions for Form 4562 (2025)
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Internal Revenue Service. One, Big, Beautiful Bill Provisions
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Internal Revenue Service. Interim Guidance on Additional First Year Depreciation Deduction (Notice 2026-11)
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Internal Revenue Service. Publication 946 (2025), How To Depreciate Property
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Office of the Law Revision Counsel. 26 US Code 50 – Other Special Rules
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Internal Revenue Service. Announcement 2024-19
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Internal Revenue Service. Topic No. 515, Casualty, Disaster, and Theft Losses
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eCFR. 26 CFR 1.1017-1 – Basis Reductions Following a Discharge of Indebtedness
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Office of the Law Revision Counsel. 26 US Code 1016 – Adjustments to Basis
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Office of the Law Revision Counsel. 26 USC 1245 – Gain from Dispositions of Certain Depreciable Property
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Internal Revenue Service. Publication 544 (2025), Sales and Other Dispositions of Assets
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Internal Revenue Service. About Form 4562, Depreciation and Amortization
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Internal Revenue Service. Instructions for Form 3468