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

A reduction in basis for depreciation is required whenever you claim a tax benefit that already recovers part of an asset’s cost before regular depreciation starts. The usual triggers are Section 179 expensing, bonus depreciation, investment tax credits, energy credits, non-taxable rebates or subsidies, canceled debt excluded from income, and casualty loss deductions. Each one shrinks what the IRS calls your depreciable basis, and that is the only figure you can recover through MACRS. Miss a reduction and the error compounds every year you own the property, then shows up again as recapture when you sell.

Basis vs. Depreciable Basis

Your starting basis in business property is what you paid for it, including purchase price, sales tax, freight, and installation labor.¹ A machine that costs $100,000 to buy, $5,000 to ship, and $5,000 to install has an initial basis of $110,000. That is the ceiling on what you can ever deduct against the asset.

Your depreciable basis is the slice of that cost that still runs through MACRS. It often starts out equal to initial basis, but it drops every time you take an upfront benefit tied to the asset. IRS Publication 551 lists the items that decrease basis: Section 179 deductions, investment credits, energy credits, non-taxable subsidies, casualty and theft losses, and certain canceled debt.² The rule behind all of them is the same. You can’t deduct a dollar you didn’t pay or that you already recovered another way.

The Order the Reductions Happen In

Form 4562 and Publication 946 lay out a fixed sequence, and the order changes the numbers.³ Work through the $110,000 machine from above.

Step 1: Section 179 Comes Off First

Section 179 lets you expense the full cost of qualifying property in the year you place it in service instead of depreciating it over time.⁴ Whatever you expense this way is subtracted from basis before anything else. Elect $50,000 under Section 179 and the remaining depreciable basis drops to $60,000.³

The annual Section 179 cap is $2,500,000, with a dollar-for-dollar phase-out once total qualifying property placed in service during the year exceeds $4,000,000.⁴ Both thresholds are indexed, so confirm the current year’s figures before you file.

Step 2: Bonus Depreciation Applies to What’s Left

Bonus depreciation runs next, against whatever basis survives the Section 179 election. For qualifying property acquired and placed in service after January 19, 2025, the rate is 100 percent in the first year.⁵ The One Big Beautiful Bill Act made that rate permanent, replacing the earlier phase-down that had bonus dropping to 40 percent for 2025.⁶

At 100 percent, bonus wipes out the remaining $60,000 in year one and leaves nothing for regular MACRS. If that is more deduction than you want, you can elect the reduced 40 percent rate (60 percent for certain long-production-period property and aircraft).⁶ At 40 percent on $60,000 you deduct $24,000 as bonus and carry $36,000 into MACRS over the asset’s class life.⁷

Step 3: Credit-Related Reductions

If the asset also generates an investment or energy credit, basis comes down again by a required percentage of that credit. Energy credits and clean electricity investment credits reduce basis by 50 percent of the credit amount; most other investment credits under Section 50 reduce basis by the full 100 percent.⁸ A $30,000 energy credit on a solar install reduces basis by $15,000. A $20,000 rehabilitation credit on a historic building reduces basis by the full $20,000. In practice you generally will not stack Section 179 with an investment credit on the same asset, so this step usually bites on property you chose to depreciate.

Step 4: Subsidies, Rebates, and Grants

Any non-taxable payment that offset your purchase price comes off last. The IRS addressed this directly for Inflation Reduction Act home energy rebates: a rebate received at purchase reduces cost basis under Section 1012, and a rebate received later triggers a basis adjustment under Section 1016.⁹ The same logic applies to state grants, utility incentives, and government subsidies on business property. Publication 551 lists subsidies for energy conservation measures and rebates treated as adjustments to sales price among the items that decrease basis.² You only depreciate what you actually paid.

Investment Credits vs. Energy Credits

The split between a 100 percent and a 50 percent basis reduction is where taxpayers most often get it wrong. Section 50(c) sets the general rule at full reduction for investment credits and carves out a 50 percent reduction specifically for energy and clean electricity credits.⁸ Treating 50 percent as the default will understate the reduction on the advanced manufacturing credit, the childcare facilities credit, the rehabilitation credit, and other investment credits in the same subpart. The trade-off Congress built in is deliberate: a credit is worth more per dollar than a deduction, so basis gives ground to prevent a double benefit.

Canceled Debt You Excluded from Income

If a lender forgave business debt and you excluded the canceled amount from income under Section 108 (insolvency, bankruptcy, qualified real property business debt, and the like), one of the required tax attribute offsets is a reduction in the basis of your depreciable property. The reduction takes effect on the first day of the tax year after the year of exclusion.¹⁰

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, and no asset can be pushed below zero.¹⁰ A Section 108(b)(5) election can concentrate the reduction on depreciable property. The sequencing gets technical quickly and is worth running past a tax professional.

Casualty Losses and Insurance Proceeds

If business property is damaged, destroyed, or stolen and you claim a casualty or theft loss, basis drops by the amount of the loss. Insurance recoveries also reduce basis: when computing the deductible loss you subtract any insurance proceeds you received or expect to receive.¹¹ For a total loss, the deductible figure is adjusted basis minus salvage value minus insurance payments. If insurance pays more than your adjusted basis, you have a gain, not a loss, and may owe tax on the difference unless you reinvest in replacement property.

Depreciation You Didn’t Claim Still Reduces Basis

Section 1016(a)(2) is the trap. Basis has to be reduced 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 put it on the return.

The damage shows up at sale. Owned a rental building ten years without claiming a dollar of depreciation? The IRS still computes your gain as if you had claimed it every year. Your basis is lower, your gain is larger, and you owe recapture on depreciation you never benefited from. You can rebut this only by proving the amount actually allowed was less than what was allowable, and that is extremely hard to document.¹³ The practical takeaway: always claim the depreciation you are entitled to.

What All Those Reductions Cost You at Sale

Every reduction you made comes back around through depreciation recapture. 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 sweeps in regular MACRS deductions, bonus depreciation, Section 179 expensing, and basis reductions tied to investment credits (net of anything already clawed back when a credit was recaptured).¹⁴ Section 179 is treated as amortization for recapture, so expensing the cost instead of depreciating it does not avoid ordinary income treatment on sale.¹³ Combine the allowed-or-allowable rule with recapture and a taxpayer who skipped depreciation for years can face a five-figure bill at closing.

Where It Goes on the Return

Form 4562, Depreciation and Amortization, is the central form. You enter the asset’s cost, subtract the Section 179 election on the form, run bonus depreciation on what remains, and send any leftover basis into the MACRS section for annual recovery.¹⁵ Credit-related reductions get folded in before the figure hits the MACRS lines.

Investment and energy credits are reported separately on Form 3468, which flows into the general business credit forms.¹⁶ The required basis reduction is handled by entering the already-reduced figure on Form 4562, not on the credit form itself.

Keep purchase invoices, documentation of rebates and grants, credit calculations, and a worksheet showing each reduction in sequence. On audit, the examiner is checking that initial cost minus Section 179 minus bonus depreciation minus credit-related reductions minus subsidies equals the figure driving your MACRS lines. A gap between those numbers is the first thing to come up.

1
Internal Revenue Service. Depreciation Frequently Asked Questions
2
Internal Revenue Service. Publication 551 – Basis of Assets
3
Internal Revenue Service. Instructions for Form 4562 (2025)
4
Office of the Law Revision Counsel. 26 US Code 179 – Election to Expense Certain Depreciable Business Assets
5
Internal Revenue Service. One, Big, Beautiful Bill Provisions
6
Internal Revenue Service. Interim Guidance on Additional First Year Depreciation Deduction (Notice 2026-11)
7
Internal Revenue Service. Publication 946 (2025), How To Depreciate Property
8
Office of the Law Revision Counsel. 26 US Code 50 – Other Special Rules
9
Internal Revenue Service. Announcement 2024-19
10
eCFR. 26 CFR 1.1017-1 – Basis Reductions Following a Discharge of Indebtedness
11
Internal Revenue Service. Topic No. 515, Casualty, Disaster, and Theft Losses
12
Office of the Law Revision Counsel. 26 US Code 1016 – Adjustments to Basis
13
Office of the Law Revision Counsel. 26 USC 1245 – Gain from Dispositions of Certain Depreciable Property
14
Internal Revenue Service. Publication 544 (2025), Sales and Other Dispositions of Assets
15
Internal Revenue Service. About Form 4562, Depreciation and Amortization
16
Internal Revenue Service. Instructions for Form 3468