How to Calculate Excess Taxable Income on Form 8990

To calculate excess taxable income on Form 8990, multiply the entity’s adjusted taxable income (ATI) by a fraction: the unused portion of the 30% ATI capacity over the full 30% capacity. Written as a formula, ETI = ATI × [(30% of ATI) − (BIE − floor plan financing interest − business interest income)] ÷ (30% of ATI).¹ The number only exists when a partnership or S corporation has 30% capacity left over after absorbing its current year business interest, and it only matters because that leftover capacity gets allocated to owners so they can deduct interest at their own level.² Getting the figure wrong cascades into partner-level errors that are expensive to fix.

Step One: Build Adjusted Taxable Income

ATI is the input the formula depends on, and it is not ordinary taxable income. Part I of Form 8990 walks through the adjustments. You begin with taxable income and strip out items so the result reflects core operating performance without the distortion of interest costs, depreciation timing, or unrelated deductions.²

Add back to taxable income:

Business interest expense, so the deduction cannot shrink the base that determines its own limit.
Any net operating loss deduction claimed under Section 172.
The Section 199A qualified business income deduction. Because QBI reduced taxable income, removing it from the ATI base means adding it back. This trips up a surprising number of preparers.³
Depreciation, amortization, and depletion, for tax years beginning after 2024. The One Big Beautiful Bill Act reinstated this add-back after it had been suspended for tax years 2022 through 2024.⁴
Capital loss carrybacks and carryovers, on Line 13.⁴

Subtract from taxable income:

Business interest income, since it already increased taxable income and the statute requires ATI to be computed without regard to it.
Items of income, gain, deduction, or loss not properly allocable to a trade or business.²

For tax years beginning after 2025, ATI also excludes income inclusions from controlled foreign corporations under Sections 78, 951(a), and 951A, along with the corresponding deductions allowed under Sections 245A(a) and 250(a)(1)(B).² If your business has significant CFC inclusions, that change can meaningfully reduce ATI, and therefore ETI, starting in 2026.

The reinstated depreciation add-back matters directly for the ETI calculation. By lifting ATI, it widens the 30% capacity, which widens the numerator of the ETI ratio whenever current year interest sits comfortably below the cap.⁵

Step Two: Measure the Unused 30% Capacity

Once you have ATI, calculate the maximum business interest the entity can deduct. The ceiling has three components that add together:²

Business interest income, which offsets interest expense dollar for dollar with no cap.
30% of ATI, which is the constraint ETI is built around.
Floor plan financing interest, which is fully deductible outside the 30% cap.

Business interest expense first absorbs against business interest income and floor plan financing interest. Only what remains gets tested against the 30% of ATI piece. That remainder is the number you plug into the ETI formula as “net business interest that needs the 30% cap,” written as BIE minus floor plan financing minus BII.

If that net figure is less than 30% of ATI, the leftover is unused capacity, and the entity has ETI. If the net figure equals or exceeds 30% of ATI, the capacity is fully consumed, ETI is zero, and the entity instead has disallowed interest.

Step Three: Apply the Ratio

With ATI, the 30% cap, and net business interest in hand, the ratio does the work:

ETI = ATI × [(30% of ATI) − (BIE − floor plan financing − BII)] ÷ (30% of ATI)

Excess taxable income is not simply ATI minus deductible interest, and that shortcut is one of the more common errors on Form 8990. The statute defines it as a proportion, so ETI is always a scaled-down slice of ATI, scaled by how much of the 30% cap sat unused.

Worked Example

A partnership has $1,000,000 in ATI, $250,000 in business interest expense, $50,000 in business interest income, and no floor plan financing interest.

The limitation is $50,000 (BII) plus $300,000 (30% × $1,000,000), which equals $350,000. The $250,000 of BIE fits well under that, so all of it is deductible.

Net business interest that needs the 30% cap is $250,000 − $50,000 = $200,000. The cap is $300,000, so $100,000 of capacity is unused. Running the formula:

ETI = $1,000,000 × ($300,000 − $200,000) ÷ $300,000 = $1,000,000 × $100,000 ÷ $300,000 = $333,333

That $333,333 of ETI gets allocated to the partners based on their distributive shares of the partnership’s nonseparately stated taxable income or loss.² When a partner adds their share of ETI to their own ATI, it raises their personal 30% capacity by exactly the right amount. A partner receiving half, or $166,667, gets $50,000 of additional capacity ($166,667 × 30%).

Why the Number Matters: What ETI Does for Owners

The calculation only matters because of what happens downstream. For partnerships, any interest the entity cannot deduct becomes excess business interest expense and is allocated to each partner on Schedule K-1, Box 13, Code K.⁶ A partner can deduct previously allocated EBIE only in a later year when the same partnership allocates them ETI. The EBIE is treated as business interest paid or accrued in the year the partner receives enough ETI to support it, and only up to that amount.² ETI from a partnership must first absorb all outstanding EBIE from that same partnership before it can increase the partner’s ATI for any other interest expense.

S corporations work differently. The disallowed interest stays inside the S corporation as a carryforward and is deducted when the entity’s own limitation has room; it does not get pushed out to shareholders as EBIE.⁷ But S corporations still compute and allocate ETI to shareholders, who then add it to their personal ATI to free up 30% capacity for interest from other activities.⁴

A pass-through entity that allocates ETI or excess business interest income to its owners must file Form 8990 even if the entity itself had no interest expense during the year.⁴ An entity with no debt is not automatically off the hook if it generates ETI for its owners.

Common Errors That Distort the Number

Three mistakes recur. First, treating ETI as “ATI minus deductible interest” instead of running the ratio. Second, subtracting the QBI deduction from the ATI base rather than adding it back. Third, forgetting that depreciation, amortization, and depletion are once again added back for tax years beginning after 2024, after being suspended for 2022 through 2024.

Any of these distortions can produce an understatement that invites the Section 6662 accuracy-related penalty, which is 20% of the underpayment attributable to negligence, disregard of rules, or a substantial understatement of income tax.⁸ An understatement is substantial if it exceeds the greater of 10% of the tax due or $5,000. For corporations, the threshold is the lesser of 10% of the tax due (or $10,000 if greater) and $10 million. Documenting every ATI adjustment line by line, and the math behind the ratio, is the most practical defense if the number is ever questioned.

1
Legal Information Institute. Excess Taxable Income – 26 USC 163(j)(4)
2
Office of the Law Revision Counsel. 26 USC 163 – Interest
3
Internal Revenue Service. Instructions for Form 8990
4
Internal Revenue Service. Instructions for Form 8990 – Limitation on Business Interest Expense Under Section 163(j)
5
Internal Revenue Service. Questions and Answers About the Limitation on the Deduction for Business Interest Expense
6
Internal Revenue Service. Partners Instructions for Schedule K-1 (Form 1065)
7
eCFR. 26 CFR 1.163(j)-6 – Application of the Section 163(j) Limitation to Partnerships and Subchapter S Corporations
8
Office of the Law Revision Counsel. 26 USC 6662 – Imposition of Accuracy-Related Penalty on Underpayments