Section 179 Business Income Limitation: Carryovers and Form 4562

The Section 179 business income limitation caps your immediate expensing deduction at the total taxable income you earn from all your active trades or businesses during the year. If your calculated Section 179 amount is larger than that income figure, you deduct only up to the income and carry the rest forward. The rule exists so that Section 179 can reduce business income to zero but never create or deepen a net loss.

What Counts as Active Business Income

The income base for the limitation is narrower than “everything on your tax return.” It picks up earnings from businesses you actively run, meaning you meaningfully participate in management or day-to-day operations. A passive investor who merely owns a stake doesn’t meet that standard.¹

These items go into the base:

Wages and salary you earn as an employee, because the IRS treats employees as actively conducting the trade or business of their employment.²
Net profit from a Schedule C sole proprietorship you actively operate.
Your share of income from a partnership or S corporation where you materially participate.
Section 1231 gains and losses from sales of property used in a trade or business you actively conduct.²
Interest earned on working capital held inside an active business.

What stays out: most rental real estate income (unless you qualify as a real estate professional under IRC Section 469), investment dividends, portfolio interest, and capital gains from stocks or other investments.³ So a business owner who earns $90,000 from active operations and $200,000 from a rental portfolio has a Section 179 income base of $90,000, not $290,000.

Adjustments That Increase the Base

You don’t pull the income base straight off your return. The regulations require you to compute it without several deductions that would otherwise shrink it:²

Add back the Section 179 deduction itself, which stops the calculation from becoming circular.
Ignore the deduction for one-half of self-employment tax under Section 164(f).
Ignore any net operating loss carryback or carryforward from other years.
Ignore deductions suspended under any other Code section.

These adjustments generally make the income base larger than the net profit line on your Schedule C, which works in your favor by giving you more room to claim the deduction. The Form 4562 instructions walk through the mechanics on Line 11.¹

Joint Filers and Multiple Businesses

On a joint return, the income base combines the active business income of both spouses. A spouse’s W-2 wages from a completely unrelated employer count, because the regulations treat employee compensation as income from the active conduct of a trade or business.²

Say you run a small manufacturing operation that earns $60,000 and your spouse earns $85,000 in salary. Your combined income base is $145,000. You can deduct up to $145,000 in Section 179 expenses even though the business that bought the equipment earned only $60,000. Without the spouse’s wages, $85,000 of the elected expense would land in a carryover year.

If you operate more than one business, the limitation applies once across all of them rather than separately to each. A taxpayer running two sole proprietorships combines the net income or loss from both into a single base. A $150,000 profit from one and a $50,000 loss from the other yields a combined base of $100,000. You then allocate the allowed deduction among your businesses as you choose.¹

How Pass-Through Entities Apply the Limit

When Section 179 flows through a partnership or S corporation, the income test runs twice. The entity first calculates its own Section 179 deduction and tests it against the entity-level income limitation. Whatever survives passes through to each partner or shareholder on Schedule K-1.

The partner or shareholder then adds the passed-through amount to any Section 179 deductions from their other active businesses and tests the combined total against their personal income base. The dual-level test blocks someone from using one entity’s deduction to shelter income unrelated to that business. If the entity’s own income limit already reduced the deduction, the individual’s personal limit can reduce it further.

Where the Income Limit Sits Among the Three Section 179 Caps

The business income limitation is the last of three constraints applied in a fixed sequence. Getting the order wrong produces the wrong deduction.

The dollar ceiling: for 2026, the maximum Section 179 deduction is $2,560,000, adjusted annually for inflation from the statutory base of $2,500,000.⁴
The investment phase-out: once total qualifying property placed in service during the year exceeds $4,090,000, the dollar ceiling drops dollar-for-dollar, phasing out entirely at $6,650,000.
The business income limitation: whatever remains after the first two limits cannot exceed your active business income for the year.⁴

An example. You place $4,190,000 of qualifying equipment in service during 2026. The investment phase-out reduces the dollar ceiling by $100,000 (the excess over $4,090,000), leaving a maximum potential deduction of $2,460,000. If your active business income is $1,800,000, the income limitation cuts the deduction to $1,800,000. The $660,000 difference carries forward.

What Happens to the Disallowed Amount

When the income limitation reduces your Section 179 deduction, the disallowed portion is not lost. It carries forward indefinitely and gets added to your Section 179 deduction in the next year that has enough income to absorb it.⁵ The carryover keeps its character as a Section 179 deduction and stays subject to the dollar ceiling, investment phase-out, and income limitation of whatever future year you use it in.⁴

One critical detail on basis: the property’s depreciable basis is reduced only by the Section 179 amount you actually deducted, not the amount you elected. If you elected $250,000 but the income limitation capped you at $180,000, the remaining $70,000 stays in the property’s basis for regular depreciation while also being tracked as a Section 179 carryover. You report the disallowed amount on Line 13 of Form 4562, which becomes next year’s starting point.¹

If You Sell the Property Before Using the Carryover

Dispose of the asset first and neither you nor the buyer can deduct the unused amount. The unused carryover gets added back to the property’s basis immediately before the sale. The increased basis reduces your taxable gain or increases your deductible loss on the disposition.⁵

Transfers by Gift or at Death

The same treatment applies to transfers at death: any unused carryover is added back to basis rather than deducted. Property received as a gift or inheritance doesn’t qualify for Section 179 in the hands of the new owner because it wasn’t acquired by purchase.⁵ If you’re carrying forward a large disallowed amount and a sale, gift, or business transition is on the horizon, it’s worth thinking about whether accelerating income into the current year would let you absorb the carryover before it converts into basis.

Choosing Between Section 179 and Bonus Depreciation When Income Is Tight

Section 179 and bonus depreciation under Section 168(k) can both apply to the same asset, but they run in sequence. Section 179 is applied first, and bonus depreciation applies to whatever cost remains. The Form 4562 instructions are explicit that you reduce the asset’s depreciable basis by the Section 179 amount before calculating any bonus depreciation.¹

The important contrast for the income limitation: bonus depreciation has no business income cap. It can create or increase a net operating loss, while Section 179 cannot. For 2026, the One Big Beautiful Bill Act restored 100% bonus depreciation for most qualifying property acquired after January 19, 2025.⁶ Property acquired before that date but placed in service during 2026 qualifies for only 20% bonus depreciation.

That gives you a planning lever. If your active business income is low relative to what you spent on equipment, electing a smaller Section 179 amount (or none at all) and relying on 100% bonus depreciation instead can generate a loss that survives as a net operating loss, whereas Section 179 would simply hit the income cap and defer the deduction. If income is strong enough to absorb the Section 179 deduction, applying Section 179 first to assets with the longest recovery periods speeds up your overall cost recovery, because those assets would depreciate the slowest under regular MACRS rules.

State Conformity

Not every state follows the federal Section 179 rules. Some states impose their own lower deduction ceilings, occasionally as low as $25,000, so a business that fully uses the federal $2,560,000 limit will need to add back a substantial amount on the state return. Other states decouple from the federal investment phase-out threshold or refuse to recognize certain types of qualifying property. Check your state’s conformity rules before assuming the federal deduction flows through unchanged.

Reporting the Calculation on Form 4562

The income limitation calculation lives in Part I of Form 4562. Line 11 is where you enter the net taxable income from all active businesses, computed with the adjustments above. Line 12 takes the smaller of Line 5 (your total elected expense after the dollar ceiling and phase-out) or Line 11, giving you the current year’s allowed deduction. Any excess appears on Line 13 as your carryforward.¹

Keep detailed records supporting the composition of your Line 11 figure. In an audit, the IRS will want to see that you excluded passive income, counted only income from businesses in which you meaningfully participated, and made the required add-backs for self-employment tax and NOL deductions. If you’re carrying disallowed amounts forward across multiple years, careful tracking matters even more, because the basis of the original asset depends on how much was actually deducted versus carried over.

1
Internal Revenue Service. Instructions for Form 4562 (2025)
2
eCFR. 26 CFR 1.179-2 – Limitations on Amount Subject to Section 179 Election
3
Office of the Law Revision Counsel. 26 USC 469 – Passive Activity Losses and Credits Limited
4
Office of the Law Revision Counsel. 26 USC 179 – Election to Expense Certain Depreciable Business Assets
5
Internal Revenue Service. Publication 946 (2025) – How To Depreciate Property
6
Internal Revenue Service. One, Big, Beautiful Bill Provisions