Reasonable Basis Standard for Tax Positions and Penalties

The reasonable basis standard for tax positions is the minimum level of legal support your return position needs to avoid the 20 percent accuracy-related penalty, and tax practitioners generally place it at roughly a 20 percent likelihood of being sustained if challenged in court. It sits above a merely non-frivolous position but below the stricter “substantial authority” and “more likely than not” thresholds. Whether your position clears this bar, and whether you disclose it properly, decides if you owe a penalty on any resulting underpayment.

Where Reasonable Basis Sits Among the Confidence Levels

Federal tax law uses a ladder of confidence levels. Each rung carries a rough probability of success if the IRS challenges you and the matter goes to court.

Not frivolous. The lowest recognized threshold, sometimes described as “not patently improper.” A frivolous position has virtually no basis in law and can trigger its own penalties. Clearing this bar alone does not protect you from accuracy-related penalties.
Reasonable basis. Approximately a 20 percent confidence level. Your position must rest on at least one recognized legal authority and amount to more than a merely arguable claim.
Substantial authority. Approximately a 40 percent confidence level. This is the default standard for avoiding the substantial understatement penalty without disclosure.
More likely than not. Greater than a 50 percent confidence level. Reserved primarily for tax shelters and certain reportable transactions.

Treasury Regulation § 1.6662-3(b)(3) defines reasonable basis as “a relatively high standard of tax reporting” that is “significantly higher than not frivolous or not patently improper.”¹ The regulation makes clear that a position that is “merely arguable” or a “merely colorable claim” does not satisfy the standard. The test is objective. Your personal belief that a deduction is valid counts for nothing if the legal authorities don’t support it.

What Counts as a Legal Authority

Your position must be grounded in at least one authority from the list Treasury recognizes under Regulation § 1.6662-4(d)(3)(iii). The regulation evaluates not just whether an authority exists, but how relevant and persuasive it is in light of your specific facts and any subsequent developments that may have weakened it.² The recognized authorities are:

The Internal Revenue Code and proposed, temporary, and final Treasury regulations interpreting it.
Revenue rulings, revenue procedures, notices, announcements, information releases, and other pronouncements published in the Internal Revenue Bulletin.
Federal court decisions at all levels, including the Tax Court, district courts, Courts of Appeals, and the Supreme Court.
Legislative history: committee reports, conference report explanations, and floor statements by a bill’s managers made before enactment.
Joint Committee on Taxation Blue Books (General Explanations of tax legislation). These carry weight for penalty purposes even though the Supreme Court has treated them as merely “persuasive” for statutory interpretation.
Private letter rulings and technical advice memoranda issued after October 31, 1976.
Actions on decisions and general counsel memoranda issued after March 12, 1981.
Tax treaties and their accompanying regulations and Treasury explanations.

Notably absent from this list: academic articles, law review commentary, tax textbooks, CPA firm white papers, and opinions from your tax advisor. These resources can help you research a position, but they carry zero weight as authorities for penalty purposes.² Relying on an authority that has been overruled, modified, or superseded by subsequent legislation likewise provides no protection.

How the Standard Protects You From Penalties

The accuracy-related penalty under IRC § 6662 equals 20 percent of any underpayment tied to negligence, disregard of rules, or a substantial understatement of income tax.³ That 20 percent is calculated on the tax shortfall itself, and the IRS charges underpayment interest on top, at 7 percent per year compounded daily as of early 2026.⁴ A $10,000 underpayment can quickly become $12,000 or more once penalty and interest stack up.

Reasonable basis interacts with the two main pieces of that penalty in different ways, and the distinction matters.

Negligence Penalty

If your position rests on a reasonable basis, the IRS cannot treat it as negligent, even without disclosure. The regulation is explicit: “A return position that has a reasonable basis… is not attributable to negligence.”¹

Substantial Understatement Penalty

Here, reasonable basis alone is not enough. You need both adequate disclosure and a reasonable basis to reduce the understatement amount. Without disclosure, you need the higher substantial authority standard to avoid this penalty.³

A “substantial understatement” for individual taxpayers means the underpayment exceeds the greater of 10 percent of the correct tax or $5,000. If you claim the qualified business income deduction under Section 199A, that percentage drops to 5 percent, making the threshold easier to cross.³

Disclosing the Position on Form 8275 or 8275-R

Because the substantial understatement penalty requires both reasonable basis and adequate disclosure, getting the disclosure right is critical. The IRS provides two forms, and using the wrong one renders your disclosure invalid.

Form 8275 handles most disclosures. You use it when your position is contrary to a rule like a statutory provision or IRS revenue ruling, or when the position simply isn’t adequately reflected elsewhere on your return.⁵ Form 8275-R applies only when your position is contrary to a Treasury regulation. Filing 8275-R signals that you are challenging the validity of the regulation itself, and the form requires you to explain why you believe the regulation is invalid. You must also demonstrate a good-faith challenge to the regulation’s validity for the disclosure to provide penalty protection.⁶

Both forms require three categories of information:

The specific return item being disclosed, including its amount and the line or schedule where it appears.
Enough factual detail for the IRS to understand the nature of the potential controversy. Vague summaries or boilerplate language will not satisfy this requirement.
The specific legal authority supporting your position, with a full citation and an explanation of how it applies to your facts. Simply naming a Code section without connecting it to your situation is not adequate.

The IRS instructions are blunt about completeness: if Form 8275 is not completed and attached to the return, the disclosure is not valid “even if the information described above is provided using another method, such as a different form or an attached letter.”⁵

Recurring and Carryover Items

For items that recur each year, such as a depreciation method, you must file a new Form 8275 every year the item appears on your return. Carryover items work differently. You disclose a carryover in the year it originates, and you do not need to file another Form 8275 for the years the carryover flows through to. The same rule applies to carrybacks: disclose in the origination year only.⁵

Filing Mechanics

Attach Form 8275 or 8275-R to your original tax return. If you missed the original filing, you may still be able to file the disclosure with a qualified amended return, but the window is narrow. A qualified amended return must be filed before the IRS contacts you about an examination, before anyone involved in the transaction is contacted about a tax shelter promotion penalty, or before a John Doe summons is served that relates to the activity.⁷ Once any of these events occurs, the amended return route is closed.

Electronic filers should confirm the form is transmitted as part of the e-file package through their tax software. A disclosure buried in a PDF attachment the IRS system doesn’t process could fail to register as a valid filing.

Where Reasonable Basis Will Not Save You

The standard has real limits, and knowing them matters as much as knowing what it covers.

Tax shelters. The reasonable basis standard does not apply to tax shelters at all. Under IRC § 6662(d)(2)(C), neither the reasonable basis reduction nor the substantial authority reduction is available for any item attributable to a tax shelter. A “tax shelter” for this purpose means any partnership, entity, investment plan, or arrangement where a significant purpose is avoiding federal income tax.³ If you participate in a tax shelter, the position needs to meet the more-likely-than-not standard to avoid penalties. Reportable transactions carry a separate disclosure regime built around Form 8886, not Form 8275, and failing to disclose one triggers its own penalties.⁸

Gross valuation misstatements. The 20 percent accuracy-related penalty doubles to 40 percent for gross valuation misstatements. A gross valuation misstatement occurs when, for example, you claim a property value at 200 percent or more of the correct amount, or when a charitable deduction property is valued so aggressively that the stated value hits the thresholds defined in IRC § 6662(h).³

Fraud. For fraud, the penalty is 75 percent of the underpayment attributable to fraudulent conduct under IRC § 6663.⁹ The IRS must show by clear and convincing evidence that some part of the underpayment was due to fraud. Once the IRS establishes fraud on any portion, the burden shifts to you to prove which portions were not fraudulent.

If Your Position Falls Short: Reasonable Cause and Good Faith

Even if your position doesn’t clear the reasonable basis bar, you may still escape the accuracy-related penalty through a separate defense under Treasury Regulation § 1.6664-4. The regulation says the single most important factor is “the extent of the taxpayer’s effort to assess the taxpayer’s proper tax liability.”¹⁰

The IRS makes this determination case by case. Situations that can demonstrate reasonable cause include an honest misunderstanding of law or fact that was reasonable given your experience and education, an isolated math or transcription error, or reasonable reliance on an information return like a W-2 or 1099 that turned out to be wrong.

Reliance on Professional Tax Advice

Hiring a tax professional does not automatically protect you. Reliance on an advisor is only a defense if the reliance was itself reasonable. To qualify, the advice must meet all of the following conditions:¹⁰

You disclosed all facts you knew or should have known were relevant. Holding back unfavorable details kills this defense.
The advice was not based on unreasonable factual or legal assumptions, including assumptions about future events.
You did not know, and had no reason to know, that the advisor lacked knowledge of the relevant area of tax law.

Even meeting these minimums doesn’t guarantee the defense succeeds. The IRS also considers your own sophistication and business experience. A seasoned real estate investor who claims to have relied on advice that a well-known anti-abuse rule doesn’t apply faces a harder sell than a first-time filer confused by a complex reporting requirement.

1
eCFR. 26 CFR 1.6662-3 – Negligence or Disregard of Rules or Regulations
2
eCFR. 26 CFR 1.6662-4 – Substantial Understatement of Income Tax
3
Office of the Law Revision Counsel. 26 USC 6662 – Imposition of Accuracy-Related Penalty on Underpayments
4
Internal Revenue Service. Interest Rates Remain the Same for the First Quarter of 2026
5
Internal Revenue Service. Instructions for Form 8275
6
Internal Revenue Service. Instructions for Form 8275-R – Regulation Disclosure Statement
7
Federal Register. Qualified Amended Returns
8
Internal Revenue Service. Instructions for Form 8886 – Reportable Transaction Disclosure Statement
9
Office of the Law Revision Counsel. 26 USC 6663 – Imposition of Fraud Penalty
10
eCFR. 26 CFR 1.6664-4 – Reasonable Cause and Good Faith Exception to Section 6662 Penalties