The general business credit: how Section 38 limits what you can actually use

Most federal business credits — the research credit, the work opportunity credit, many energy credits — do not stand alone. Section 38 pools them into a single "general business credit," and Section 38(c) caps how much of that pool can offset tax in any year: net income tax minus the greater of the tentative minimum tax or 25% of net regular tax liability above $25,000. Whatever the cap strands carries back one year and forward twenty under Section 39, absorbed oldest-first.

That machinery — stack, cap, carry — determines whether a credit computed on a study is cash this year, cash in 2031, or a deduction-value scrap in 2046. Practitioners who model the credit but not the limitation routinely overstate the benefit.

How Section 38 stacks the credits

Section 38(b) lists the component credits — several dozen, from the investment credit to the research credit under Section 41 to the employer-provided childcare credit — and sums them into the current-year general business credit. Order matters within the stack: Section 38(d) absorbs the components in the order listed in 38(b), which controls which credit is treated as used when the cap bites and therefore which credit carries forward. The full text is worth reading directly at the Internal Revenue Code; summaries reliably omit the ordering rules.

The aggregation has a practical consequence: a taxpayer claiming both a research credit and, say, a work opportunity credit does not get two separate limitations. They compete for the same headroom.

What does the Section 38(c) limitation actually allow?

The formula: the credit allowed for the year cannot exceed the excess of net income tax over the greater of (i) the tentative minimum tax or (ii) 25% of net regular tax liability above $25,000.

For C corporations, the pre-2018 corporate AMT's tentative minimum tax is treated as zero for this purpose (the new corporate alternative minimum tax runs on separate rails — more below), so prong (ii) usually controls. Worked numbers:

A corporation with $500,000 of net income tax and $600,000 of available Section 38 credits can use only $381,250 of them this year.

Credit usable this year$381,250

Tax that must still be paid (25% floor)$118,750

Credit carried to other years$218,750

Worked example from this article; assumes a C corporation with tentative minimum tax of zero.

The 25% floor is the point: Congress decided profitable taxpayers should not zero out with credits. Roughly a quarter of regular tax above the first $25,000 is always payable, no matter how large the credit pool. For individuals and passthrough owners, the tentative minimum tax prong is live — a taxpayer in the AMT zone can find prong (i) far more restrictive than the 25% floor, and "specified credits" under Section 38(c)(4), including eligible small business research credits in certain years, get relief from the TMT prong. Check the current statute; this subsection has been amended repeatedly.

Section 39: one back, twenty forward, oldest first

Excess credit is not lost — yet. Section 39 carries it back one year (a refund claim for last year, filed on Form 1045/1139 or an amended return, subject to the refund statute of limitations) and forward twenty years.

Absorption is strictly FIFO under Section 38(d): in any year, carryforwards are used oldest vintage first, then the current-year credit, then carrybacks into that year. Three consequences:

1. Vintage tracking is mandatory. A taxpayer with 2019, 2022, and 2025 credits must know which dollars were absorbed in which year — Form 3800 requires it, and Section 383 (below) makes it matter at exit.
2. The current-year credit is the one that carries. Because old credit absorbs first, a taxpayer generating credit faster than the cap allows pushes each new year's credit further down the queue.
3. Expiry is real. After year twenty, Section 196 permits a deduction for certain expired credits, including the research credit — worth 21 cents on the dollar to a corporation instead of 100. The carryforward mechanics for the research credit specifically follow this same schedule.

What happens to credit carryforwards after an ownership change?

Section 383 imports the Section 382 regime: after an "ownership change" — a more-than-50-percentage-point shift in 5% shareholders over a three-year testing period — pre-change credits can offset only the tax liability attributable to the annual Section 382 limitation (loss-company equity value times the long-term tax-exempt rate, a rate that has hovered in the low single digits). The mechanics live in Treas. Reg. §1.383-1, on eCFR Title 26.

The arithmetic is brutal for credit-heavy startups. A company worth $10 million at change with a 3.5% rate has a $350,000 annual income limitation; the credit usable each year is only the tax on that sliver — at 21%, about $73,500 of credit per year, against a carryforward that may run into the millions. Venture-backed companies routinely trigger ownership changes at financing rounds without noticing. Any acquirer pricing a target's Form 3800 balance should assume a Section 383 haircut until a study proves otherwise.

Credits against BEAT and the corporate AMT

Two parallel minimum-tax regimes interact with the credit pool, briefly:

• BEAT (Section 59A). The base erosion minimum tax is computed by comparing 10% of modified taxable income to regular tax reduced by credits — so credits, by lowering the comparison baseline, can mechanically increase BEAT. The statute carves partial protection for the research credit and certain Section 38 credits in the computation; the interaction is a Form 8991 exercise, not an afterthought.
• Corporate AMT (CAMT). The 15% book-minimum tax enacted in 2022 is not reduced by general business credits. A CAMT payer can find fresh research credits unusable in the CAMT year, though the resulting CAMT credit and the Section 39 carryforward both preserve value for later regular-tax years.

Neither regime eliminates credit value; both defer it, sometimes for years.

Why do unusable credits pile up, and what should you do?

Credits accumulate when generation outruns the cap: pre-profit startups, loss years, NOL-sheltered income (an NOL deduction reduces the tax the credit needs to offset), Section 383 events, and CAMT years. A large Form 3800 carryforward schedule is common; a managed one is not. The toolkit:

• Elect the payroll offset if eligible. Qualified small businesses can apply up to $500,000 of research credit against payroll taxes via Form 8974 — converting a stranded income-tax credit into near-term cash. The election is only available on a timely filed original return; see the planning-calendar consequences.
• Model the 280C election annually. The reduced-credit election trades credit size for deduction size; a taxpayer who cannot use the credit for a decade may prefer the deduction now. This is the classic credits-versus-deductions trade with a time-value twist.
• Sequence deductions and credits. Accelerating deductions (bonus depreciation, Section 174A expensing) into a year with expiring-vintage credits can be exactly wrong — it shrinks the tax base the old credit needed. Sometimes the right move is to slow deductions.
• Protect vintages in M&A. Pre-transaction Section 382/383 studies, and purchase agreements that price the haircut.

When the limitation analysis does not matter

If the taxpayer pays substantial regular tax every year, generates modest credits, and has stable ownership, Section 38(c) is a formality — Form 3800 absorbs everything and this article is trivia. The machinery matters at the margins: startups, loss companies, acquisitions, minimum-tax payers, and anyone whose credit study produces a number larger than a quarter of their tax bill. For those taxpayers, the limitation — not the credit computation — is where the modeling belongs, and it is also where the IRS looks least and the calendar punishes most.