The 20% Penalty Under §6662 — and the One-Page Form That Can Switch It Off

Published: August 9, 2026 · Reading time: 11 min

TL;DR: Nearly every tax-strategy guide argues about whether a deduction is allowed. This one prices being wrong. §6662 adds 20% of the underpayment — not 20% of the deduction — and it reaches freelancers through two limbs: negligence (no records, a figure nobody can reconstruct) and substantial understatement, which for an individual means an understatement exceeding the greater of 10% of the tax required to be shown or $5,000. Below about $50,000 of correct tax, that threshold is simply $5,000 of understated tax. Three defences exist and they do not overlap: substantial authority works silently and alone; reasonable basis + disclosure on Form 8275 works only as a pair for the substantial-understatement limb, though the reasonable basis alone defeats negligence as to a position under Reg. §1.6662-3(b)(1); and §6664(c) reasonable cause reaches everything, including the one thing neither of the others touches — a substantiation failure, which is also negligence and which Reg. §1.6662-3(c)(1) excludes from the disclosure exception. That last gap is decided on records you either kept in June or did not.

Ninety-five of this corpus's tax-strategy posts help you decide what to claim. This one is about the layer underneath all of them: what happens when the answer you chose turns out to be wrong.

The penalty is on the tax, not on the deduction

The single most common misreading. §6662 applies 20% to the portion of the underpayment attributable to the failure — not 20% of the disallowed expense.

A disallowed $8,000 deduction for a freelancer at a 34.5753% combined marginal rate produces roughly $2,766 of extra tax, and the penalty is 20% of that — about $553. That is smaller than people fear.

What is larger than people expect is the total package, because three things arrive together (assuming the negligence limb, which has no threshold — the underpayment here is below the substantial-understatement floor set out further down):

And an examination rarely finds one item. The same reasoning that disallowed this year's deduction usually applies to the two other open years, which is how a single habit becomes a three-year assessment.

The two limbs that reach freelancers

§6662 lists several grounds. Two of them are the ones that show up in ordinary freelance examinations, and they behave completely differently.

Negligence, or disregard of rules and regulations

This is about your conduct. Failing to make a reasonable attempt to comply: a deduction with nothing behind it, income reported to you on a form you did not put on your return, a number that cannot be reconstructed from anything.

It is the limb most freelancers are actually exposed to, and — this is the important part — it is the one disclosure cannot touch.

Substantial understatement of income tax

This is arithmetic, and it does not care why you were wrong. For an individual, the Form 8275 instructions state the test: an understatement that

exceeds the greater of: 10% of the tax required to be shown on the return for the tax year, or $5,000

Two limbs and a floor. Note what the floor does: 10% of the correct tax only exceeds $5,000 once the correct tax exceeds $50,000. For most freelancers, the operative threshold is simply $5,000 of understated tax — a much lower bar than "10%" makes it sound.

Worked example: how close $5,000 actually is

Rowan is a freelance consultant. His filed return showed $24,900 of tax. On examination the correct figure is $31,400.

So Rowan owes $6,500 of tax, $1,300 of penalty, and interest from the original due date — $7,800 before interest, on a return that understated the correct tax by 20.7%.

Notice the 10% limb never binds here. It would have taken $50,000 of correct tax before 10% overtook the $5,000 floor. At freelance income levels, "substantial" means $5,001.

The three defences, and what each one actually covers

Substantial authority — the quiet one

The strongest defence and the only one that works silently. If the authorities supporting your treatment are substantial in relation to those opposing it, the item is removed from the substantial-understatement computation entirely — no form, no flag, nobody the wiser.

Reasonable basis plus disclosure — the paired one

The Form 8275 instructions describe the form as disclosing

items or positions, except those taken contrary to a regulation, that are not otherwise adequately disclosed on a tax return to avoid certain penalties

and specify what it reaches: the portions of the accuracy-related penalty due to disregard of rules or to a substantial understatement of income tax for non-tax-shelter items, provided the position has a reasonable basis.

Three limits fall straight out of that sentence, and each one defeats a common misuse:

1. The disclosure does nothing against negligence — the instructions say so explicitly. Be precise about what that means, because it is not that reasonable basis is useless there: Reg. §1.6662-3(b)(1) provides that "a return position that has a reasonable basis … is not attributable to negligence," so the position half of the pair defeats the negligence limb on its own, with no form filed. What neither half reaches is the other branch of the same limb — the regulation adds that negligence "also includes any failure by the taxpayer to keep adequate books and records or to substantiate items properly," and Reg. §1.6662-3(c)(1) excludes exactly that case from the disclosure exception. So a freelancer with no receipts who files Form 8275 has bought nothing and has attached a spotlight to the item — not because disclosure never helps, but because a substantiation failure is the one thing it cannot cure.
2. Reasonable basis still has to be there underneath. The instructions call it "a relatively high standard of tax reporting that is significantly higher than not frivolous or not patently improper." Disclosure is a multiplier on a position, not a substitute for one.
3. Contrary to a regulation is a different form. Use Form 8275-R — a more exposed posture that deserves professional advice before you take it.

On the percentages you will see quoted elsewhere: the regulations frame substantial authority and reasonable basis by the weight of the authorities, not by a numeric probability. The familiar "roughly 40%" and "roughly 20%" are practitioner shorthand with no authority behind them, and citing them as if they were the standard is its own small error. The usable question is: can you name the authorities on your side?

§6664(c) reasonable cause — the broad one

The widest of the three, because it reaches every limb including negligence. It removes the penalty for any portion of an underpayment where you show reasonable cause and good faith.

It is decided on facts, and the most important factor is the extent of your effort to assess the correct liability. Which means it is built out of ordinary artefacts:

• Contemporaneous records rather than reconstructions — the same reason a mileage log kept as you drove outperforms one rebuilt afterwards
• A written note of why you treated something the way you did, made at the time
• Where you relied on a professional, evidence that they had the complete and accurate facts

That last condition is where reliance defences collapse most often. Advice given on incomplete information protects nobody, and neither does a preparer handed a summary total with no documents underneath it.

Reasonable cause is not a decision you make in April. It is the by-product of a records habit maintained all year — which is why it is the defence a freelancer can actually control.

When disclosure is a good idea, and when it is not

Reach for Form 8275 when:

• The position has a genuine reasonable basis and you can name the authorities
• The amount is large enough that a substantial understatement is realistic if you lose
• The treatment is unusual on its face — an allocation an examiner would question, a characterisation that differs from the form you received, a method change

Do not reach for it when:

• The real exposure is negligence — missing records, unsupported figures. Disclosure does not reach it, and the form advertises the item.
• You have substantial authority. You already have the better defence and it requires saying nothing.
• The item is routine and already visible on the return. The instructions note that guidance is published annually in a revenue procedure identifying circumstances where an item reported on a return is already adequate disclosure, and that no Form 8275 is needed for items meeting it.

That third bullet is worth taking seriously. Filing an unnecessary Form 8275 is not neutral — you have hand-labelled an item for review, in exchange for protection you already had.

The part that actually moves the number

Everything above concerns what happens after an examination begins. The two inputs a freelancer genuinely controls are earlier:

• Whether the understatement clears $5,000 at all. Below the threshold, the substantial-understatement limb never engages. Ordinary accuracy — reconciling 1099s to gross receipts, not guessing at business-use percentages — is what keeps you under it.
• Whether reasonable cause is available. It depends entirely on records that either exist contemporaneously or do not. This defence is decided in June, not in April.

Both of those are recordkeeping, not tax planning. Which is the quiet conclusion of a post about penalties: the cheapest defence against §6662 is the one you build by accident, every week, by keeping the thing that proves the number.

Frequently Asked Questions

What is the section 6662 accuracy-related penalty and when does it apply?

It is a penalty of 20 percent of the portion of an underpayment attributable to any of several listed failures, and the two that reach ordinary freelancers are negligence or disregard of rules and regulations, and any substantial understatement of income tax. Negligence means failing to make a reasonable attempt to comply — no records behind a deduction, income you did not report that was on a form sent to you, a figure nobody can reconstruct. A substantial understatement is arithmetic rather than a judgement about your conduct: for an individual it is an understatement exceeding the greater of 10 percent of the tax required to be shown on the return for the year, or $5,000. The distinction matters because the two limbs have different defences. The penalty applies to the underpayment, not to the deduction, so it is 20 percent of extra tax rather than 20 percent of the disallowed expense, and it stacks with interest that runs from the original due date. There is also a 40 percent rate for gross valuation misstatements and undisclosed noneconomic-substance transactions, which is well outside ordinary freelance territory.

What does Form 8275 actually protect against?

Less than most people assume, and it is important to know which parts before relying on it. The Form 8275 instructions say the form is filed to disclose items or positions, except those taken contrary to a regulation, that are not otherwise adequately disclosed on a tax return to avoid certain penalties — specifically the portions of the accuracy-related penalty due to disregard of rules or to a substantial understatement of income tax for non-tax-shelter items, if the return position has a reasonable basis. Read that carefully and three limits fall out. First, the disclosure itself does nothing against the negligence limb, which the instructions state explicitly — though be precise about what that means, because Regulation 1.6662-3(b)(1) provides that a return position which has a reasonable basis is not attributable to negligence, so the reasonable-basis half of the pair defeats that limb on its own without any form being filed. What neither half reaches is the branch of negligence the same regulation describes as any failure to keep adequate books and records or to substantiate items properly, which Regulation 1.6662-3(c)(1) expressly excludes from the disclosure exception. So a freelancer with no records who files Form 8275 has bought no protection at all, not because disclosure never helps but because a substantiation failure is the one thing it cannot cure. Second, it requires a reasonable basis underneath it — the instructions describe that as a relatively high standard significantly higher than not frivolous or not patently improper, so disclosure does not rescue a position with nothing behind it. Third, a position taken contrary to a regulation needs Form 8275-R instead, which is a different and more exposed posture.

What is a substantial understatement of income tax for a freelancer?

For an individual it is an understatement that exceeds the greater of 10 percent of the tax required to be shown on the return for the tax year, or $5,000. That is a two-part test with a floor, and the floor is what catches freelancers at ordinary income levels. Consider a return showing $24,900 of tax when the correct figure was $31,400. The understatement is $6,500. Ten percent of the tax required to be shown is $3,140, and the greater of that and $5,000 is $5,000. Because $6,500 exceeds $5,000, the understatement is substantial and a 20 percent penalty of $1,300 is on the table on top of the $6,500 of tax and the interest running from the original due date. Notice that the 10 percent limb never binds until the correct tax exceeds $50,000, so for most freelancers the operative threshold is simply $5,000 of understated tax. The trigger is the size of the error, not its cause — the same $6,500 arrives here whether it came from an aggressive position or a spreadsheet mistake.

What is the difference between substantial authority and reasonable basis?

They are two different standards protecting against two different things, and they sit at different heights. Substantial authority is the stronger one and it works on its own: if the authorities supporting your treatment are substantial in relation to those opposing it, the item is removed from the substantial-understatement computation without any disclosure at all, and nobody need ever know you thought about it. Reasonable basis is the lower standard and it only works when paired with disclosure — the Form 8275 instructions describe it as a relatively high standard of tax reporting that is significantly higher than not frivolous or not patently improper, and the protection arrives only when the position is disclosed. The regulations frame both standards by reference to the weight of authority rather than by a numeric probability, so the familiar practitioner shorthand of roughly forty percent for substantial authority and twenty percent for reasonable basis has no authority behind it and should not be cited as though it did. The practical question is simply whether you can name the authorities on your side.

Can I avoid the penalty by showing reasonable cause?

Yes, and it is the broadest defence of the three because it reaches every limb of the penalty including negligence, which disclosure does not. The reasonable-cause exception in section 6664(c) removes the penalty for any portion of an underpayment where you show there was reasonable cause and you acted in good faith. In practice that is decided on facts rather than on a form: the most important factor is the extent of your effort to assess the correct liability, and the defence is built out of the ordinary artefacts of having tried. Contemporaneous records rather than reconstructions, a mileage log kept as you drove, a written note of why you treated something the way you did, and where you relied on a professional, evidence that they had the complete and accurate facts. That last condition is where reliance defences most often collapse — advice given on incomplete information protects nobody, and neither does a preparer who was handed a summary total with no underlying documents. Reasonable cause is not a filing decision made in April; it is the by-product of a records habit maintained all year.

Authoritative References

• IRS — Instructions for Forms 8275 and 8275-R
• IRS — About Form 8275, Disclosure Statement
• IRC §6662 — Imposition of accuracy-related penalty on underpayments
• IRC §6664 — Definitions and special rules, including the reasonable cause exception
• Treas. Reg. §1.6662-4 — Substantial understatement of income tax
• IRS — Accuracy-Related Penalty

Related reading: Audit-proof business expenses · Contemporaneous mileage log requirements · The Cohan rule and lost receipts · IRS audit document requests · Schedule C audit triggers

The Only §6662 Defence You Control Is Built in June

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This guide is general education for U.S. freelancers and Schedule C filers in 2026. It is not personalized tax advice — whether a position has substantial authority or a reasonable basis, and whether to disclose it, are judgements to make with a CPA or EA before the return is filed, not afterwards.