Form 8990: The Business Interest Deduction Limit

Key Takeaways

• Form 8990 caps deductible net business interest under Section 163(j) of the tax code.
• The limit is business interest income plus 30% of adjusted taxable income plus floor plan financing.
• Small businesses under the gross receipts test ($31 million for 2025) are generally exempt.
• Disallowed interest carries forward indefinitely until adjusted taxable income allows the deduction.

What the Form 8990 Business Interest Limitation Is

Section 163(j) limits how much interest a business can deduct when its borrowing is large relative to its earnings. Form 8990 is where the business runs that calculation, reports the deductible amount, and tracks any interest pushed into future years.

The rule targets net interest expense, meaning interest paid minus interest earned. It applies to most businesses above a size threshold, including partnerships and S corporations, which compute the limit at the entity level and pass results through on Schedule K-1.

The Intuition

Before this rule, a company could load up on debt and deduct all the interest, shrinking taxable income sharply. Congress capped that to limit the tax advantage of heavy leverage over equity financing.

The cap ties the deduction to earnings. A business that earns more can deduct more interest. A business with thin or negative earnings deducts less, even if it owes the same interest. This makes the rule bite hardest in downturns, exactly when leveraged firms are already stressed.

How It Works

The deductible amount is the sum of three pieces:

Deductible business interest = business interest income
                             + 30% of adjusted taxable income (ATI)
                             + floor plan financing interest

Adjusted taxable income (ATI) is the base. It starts from taxable income and removes business interest, then adds or subtracts other items defined in the regulations. The definition of ATI has shifted over time, so the current Form 8990 instructions control which addbacks apply for the year.

Any net interest above the cap is disallowed for the year. Under 26 U.S.C. 163(j), that disallowed amount carries forward indefinitely. It becomes deductible in a later year when ATI is high enough to absorb it.

The small business exemption spares most smaller firms. A business with average annual gross receipts at or below the inflation-adjusted threshold, $31 million for tax years beginning in 2025, generally does not have to apply the limit. Tax shelters do not qualify regardless of size.

Worked Example

A company has the following for the year:

Business interest expense:   $5,000,000
Business interest income:      $200,000
Adjusted taxable income:    $12,000,000
Floor plan financing:                $0

The deduction cap is:

$200,000 + (30% x $12,000,000) + $0
= $200,000 + $3,600,000
= $3,800,000

Net interest expense is $5,000,000 minus $200,000 of interest income, or $4,800,000. The company can deduct $3,800,000 this year.

Disallowed interest = $4,800,000 - $3,800,000 = $1,000,000

That $1,000,000 carries forward. If next year's ATI rises, the company can deduct the carryforward then. If ATI falls, the carryforward keeps growing.

Common Mistakes

1. Assuming you are exempt. The small business exemption uses aggregation rules under Section 448(c). Related entities are combined, so a small standalone unit inside a larger group may still be subject to the limit.
2. Using the wrong ATI definition. The addbacks that build ATI have changed across tax years. Relying on an old worksheet can overstate or understate the cap.
3. Forgetting the carryforward. Disallowed interest is an asset that reduces future tax. Failing to track it on Form 8990 wastes a real deduction.
4. Ignoring pass-through mechanics. Partnerships apply the limit at the entity level, and excess items pass to partners with their own carryforward rules. Treating the K-1 amount as fully deductible is a common error.
5. Overlooking floor plan financing. Dealers that finance inventory get extra deduction room. Omitting floor plan interest understates the cap for those businesses.

Frequently Asked Questions

What is the Form 8990 business interest limitation in simple terms? The Form 8990 business interest limitation caps how much loan interest a business can deduct in a year, tied to its earnings. Interest above the cap carries forward to later years.

How does the Form 8990 business interest limitation affect investment decisions? It reduces the tax benefit of heavy debt, so highly leveraged companies may not deduct all their interest in lean years. Analysts watch the carryforward as a sign of leverage stress.

What is a real-world example of the business interest limitation? A company with $4.8 million of net interest but only $3.8 million of allowed deduction must carry $1 million forward, paying tax on income it could not offset with interest this year.

How can businesses use the rule effectively? Confirm whether the small business exemption applies after aggregation, track disallowed interest carryforwards each year, and time discretionary income to lift adjusted taxable income when needed.

How is the business interest limitation different from interest coverage? Interest coverage is a credit ratio measuring whether earnings can pay interest. The Section 163(j) limit is a tax rule capping the deduction, using its own adjusted taxable income definition.

Sources

1. IRS. Instructions for Form 8990 (Rev. December 2025). https://www.irs.gov/instructions/i8990
2. IRS. About Form 8990, Limitation on Business Interest Expense Under Section 163(j). https://www.irs.gov/forms-pubs/about-form-8990
3. IRS. Questions and answers about the limitation on the deduction for business interest expense. https://www.irs.gov/newsroom/questions-and-answers-about-the-limitation-on-the-deduction-for-business-interest-expense
4. Cornell Legal Information Institute. 26 U.S.C. 163. https://www.law.cornell.edu/uscode/text/26/163

Disclaimer

This article is educational content only and is not financial advice. Nothing here is a recommendation to buy, sell, or hold any security. Consult a licensed advisor before making investment decisions.