An audit is stressful enough without an extra bill tacked on top. But if the IRS decides your return was wrong in the wrong way, it doesn’t just ask you to pay the difference, it can charge an accuracy-related penalty of 20% (or more) of the underpayment. On a $25,000 understatement, that’s an extra $5,000 before interest even starts compounding.
The good news: this penalty is largely avoidable, and even when it’s assessed, it can often be reduced or removed. Here’s what triggers it, how it’s calculated, and what actually works to stay clear of it, and what to do if a notice has already landed in your mailbox.
What Is the IRS Accuracy-Related Penalty?
The accuracy-related penalty is authorized under Internal Revenue Code § 6662. It applies when the IRS determines that part of your tax underpayment resulted from one of several specific problems, not just any mistake. Unlike the failure-to-file or failure-to-pay penalties, this one is about the quality of the return itself: did you take reasonable care, and did you report a defensible number?
The standard penalty rate is 20% of the underpayment attributable to the problem. In cases involving significant overvaluation of property, the rate can jump to 40%. Importantly, these penalties don’t stack, if the same underpayment is due to more than one type of error, the IRS applies only the single highest applicable rate, not a combined total.
What Triggers an Accuracy-Related Penalty
IRC § 6662(b) lists several grounds for the penalty. The two that show up in the vast majority of cases are:
1. Negligence or Disregard of Rules and Regulations
“Negligence” in tax law doesn’t require intent to cheat, it just means you failed to make a reasonable attempt to comply. The IRS and courts have treated the following as evidence of negligence:
- Failing to report income that was documented on a W-2, 1099, K-1, or similar form
- Claiming deductions or credits without records to support them
- Not keeping adequate books and records
- Careless math or transposition errors that a basic review would have caught
- Taking a position on a return that has no reasonable basis in the law
2. Substantial Understatement of Income Tax
This one can apply even if you didn’t do anything careless, it’s essentially a math threshold. For individuals, an understatement is “substantial” if it’s more than the greater of 10% of the tax required to be shown on the return, or $5,000. (If you claim the Section 199A qualified business income deduction, that 10% threshold drops to 5%.) For C corporations, the threshold is the lesser of 10% of the tax due (or $10,000 if greater) or $10 million.
3. Substantial or Gross Valuation Misstatements
If you claim a value or basis for property that turns out to be significantly overstated, a separate penalty applies:
- Substantial valuation misstatement: the claimed value is 150% or more of the correct value, 20% penalty
- Gross valuation misstatement: the claimed value is 200% or more of the correct value, 40% penalty
- Similar rules apply to substantial and gross valuation understatements on estate and gift tax returns
4. Other Less Common Triggers
Section 6662 also covers substantial overstatements of pension liabilities, undisclosed foreign financial asset understatements, and reportable transaction understatements (addressed under the related IRC § 6662A). These are far less common for individual filers but carry the same 20% baseline rate.
How the Penalty Is Calculated
The math is simpler than the statute makes it look:
Penalty = 20% (or 40%) × the portion of the underpayment caused by the triggering issue
For example, if the IRS determines you understated your income tax by $20,000 due to unreported income, the accuracy-related penalty is $4,000. That’s on top of the $20,000 you owe, plus interest that accrues from the original due date of the return.
The penalty applies only to the portion of the underpayment tied to the specific problem, not your entire tax bill, so a single missed 1099 usually doesn’t put your whole return at risk of the higher rate, though it can still be enough to cross the “substantial understatement” threshold.
How to Avoid the Penalty in the First Place
Most accuracy-related penalties trace back to a handful of avoidable habits. Here’s what actually reduces your exposure:
- Reconcile every income document against your return. Cross-check every W-2, 1099-NEC, 1099-MISC, 1099-K, 1099-INT/DIV, and K-1 against what you reported. The IRS matches these automatically, and mismatches are the single most common audit trigger.
- Keep contemporaneous records for every deduction and credit. “I remember spending about that much” is not a defense. Receipts, mileage logs, bank statements, and invoices, kept at the time, not reconstructed later, are what actually hold up.
- Disclose uncertain positions. If you’re taking a return position that’s arguably correct but not a slam dunk, IRS Form 8275 (Disclosure Statement) or 8275-R can protect you from the substantial-understatement penalty even if the IRS later disagrees with your position, as long as the position had a reasonable basis.
- Get a second look on anything unusual. Large deductions, home office claims, crypto transactions, rental losses, and business use of vehicles are all areas where a qualified preparer or tax professional catches errors before they become penalties.
- Don’t guess on valuations. If a return depends on the value of property, a donated asset, closely held stock, real estate in an estate, get a qualified, independent appraisal rather than an informal estimate.
- File electronically and double-check math. E-filing software catches most arithmetic errors automatically, which eliminates one of the most common negligence findings.
What If You’ve Already Been Assessed the Penalty?
You have more options than you might think:
Reasonable cause and good faith. IRC § 6664(c) provides a full exception to the penalty if you can show you acted with reasonable cause and in good faith. The IRS weighs factors like your effort to determine the correct tax, your experience and education, and whether you relied on a competent tax professional who had all the relevant facts. Reliance on a paid preparer is a strong defense, but only if you gave them accurate and complete information.
First-Time Abate. If you have a clean compliance history for the prior three years (no penalties, all returns filed, all taxes paid or on a payment plan), you may qualify to have the penalty removed administratively, regardless of the underlying reason.
Formal protest or Tax Court. If the penalty was assessed as part of an audit, you can dispute it through the IRS Independent Office of Appeals, and, if necessary, in U.S. Tax Court.
Facing an accuracy-related penalty notice right now? The window to protest is short, and the facts you present at this stage shape everything that follows. Talk to a Tax Law Advocates attorney about your notice before you respond, our team is led by tax attorneys and enrolled agents who handle these disputes daily, from the first IRS letter through full resolution.
The Bottom Line
The accuracy-related penalty exists to punish careless or unsupportable returns, not honest mistakes made with reasonable care. The best protection is straightforward: report every dollar shown on a tax document, back up every deduction with real records, disclose genuinely uncertain positions, and get professional help when a return gets complicated. If a penalty still lands, reasonable-cause relief and first-time abatement resolve a meaningful share of cases, but they require acting quickly and documenting your case well.
If you’re facing an active audit or have already received a penalty notice, it’s worth having a tax attorney or enrolled agent review the specific IRS notice before you respond, the deadline to protest is short, and the facts you present at that stage shape everything that follows.
FAQ
Is the accuracy-related penalty the same as a fraud penalty? No. Fraud penalties (IRC § 6663) apply when the IRS can show intentional deception and carry a much higher 75% rate. Accuracy-related penalties don’t require proof of intent, carelessness or an unsupported position is enough.
Can I be charged both a substantial-understatement and a negligence penalty on the same underpayment? No. The penalties don’t stack. If the same portion of underpayment qualifies under more than one category, the IRS applies only one 20% (or 40%) rate to that portion.
Does relying on a CPA automatically protect me from the penalty? Not automatically, but it helps significantly. You need to show you gave the preparer complete and accurate information and reasonably relied on their advice. If you withheld information or the advice was clearly unreasonable on its face, reliance won’t shield you.
How long does the IRS have to assess an accuracy-related penalty? Generally the same three-year statute of limitations that applies to the underlying tax assessment, extended to six years if income was understated by more than 25%, and unlimited in cases of fraud or a failure to file.
