Reasonable cause is the defense that does the most work in crypto penalty cases. It applies to the 20 percent accuracy penalty, it can apply to the fraud penalty, and a parallel standard applies to the failure to file and pay additions. It is also the defense most often argued badly.

Here is what the law actually requires, how it applies to crypto facts, and how to build the record that wins it.

For the accuracy and fraud penalties, IRC 6664(c)(1) says no penalty is imposed under 6662 or 6663 for any portion of an underpayment if it is shown that there was reasonable cause for that portion and that the taxpayer acted in good faith.

For the failure to file and failure to pay additions, IRC 6651(a) uses a related phrase: the addition applies “unless it is shown that such failure is due to reasonable cause and not due to willful neglect.”

Treas. Reg. 1.6664-4(b)(1) explains how the accuracy penalty defense is judged. The determination is made case by case, on all the facts and circumstances, and “generally, the most important factor is the extent of the taxpayer’s effort to assess the taxpayer’s proper tax liability.”

Effort. Not intentions, not confusion, not how unfair the rules seem. Effort.

What the regulation says can count

Treas. Reg. 1.6664-4(b)(1) lists circumstances that may indicate reasonable cause and good faith:

  • An honest misunderstanding of fact or law that is reasonable in light of the facts and circumstances, including your experience, knowledge and education.
  • An isolated computational or transcriptional error, which the regulation says generally is not inconsistent with reasonable cause and good faith.
  • Reasonable reliance on an information return, such as a Form 1099, if you did not know or have reason to know it was wrong.
  • Reasonable reliance on professional advice, subject to the requirements in 1.6664-4(c).

Each of those comes with conditions, and crypto cases test them.

Relying on a Form 1099-DA

The regulation says reliance on erroneous information reported on an information return indicates reasonable cause and good faith, provided you did not know or have reason to know the information was incorrect. It adds that you generally have reason to know if the information is inconsistent with other information reported or furnished to you, or with your own knowledge of the transaction.

Crypto investors usually know their own transactions better than any broker form. If a 1099-DA showed no basis for coins you bought elsewhere, you knew your basis was not zero. If it showed a transfer as a sale, you knew you did not sell. Reliance on an obviously incomplete form is a weak defense. Reliance on a form that looked right and was wrong in a way you could not have spotted is a strong one. See how to handle a wrong 1099-DA.

Relying on a preparer

Treas. Reg. 1.6664-4(c) sets minimum requirements for reliance on advice. The advice must be based on all pertinent facts and circumstances, and the requirements are not met “if the taxpayer fails to disclose a fact that it knows, or reasonably should know, to be relevant.” The advice must not rest on unreasonable factual or legal assumptions. And reliance may not be reasonable if you knew or should have known the advisor lacked knowledge in the relevant area of federal tax law.

The regulation’s own examples make the line clear. Example 1: a taxpayer who gave a professional full details and followed the advice demonstrated good faith. Example 2: a taxpayer who followed a friend’s tax tip without further inquiry did not.

For crypto, the question is almost always disclosure. Did you give your preparer every exchange, every wallet, every staking reward? If you handed over one 1099 and kept quiet about the rest, reliance fails. If you handed over everything and the preparer got it wrong, you may have a real defense.

Relying on software

Many crypto taxpayers relied on tax software or crypto tax calculators. The regulation does not address software by name. Under its general rule, reliance on facts that turn out to be wrong “does not necessarily demonstrate reasonable cause,” but reliance is reasonable cause if, under all the circumstances, it was reasonable and you acted in good faith.

Software reliance tends to work when you imported complete data, the tool made a computational error you could not reasonably catch, and you had no warning signs. It tends to fail when data was missing because you never connected some accounts, or when you ignored the tool’s own warnings about unmatched transfers or missing basis.

Late filing and late payment: a different test

For the failure to file and pay additions, the statute asks whether the failure was “due to reasonable cause and not due to willful neglect.” IRC 6651(a). That is not the same wording as 6664(c)(1), and the facts that matter are different. The question is why the return was late or the tax unpaid, not why an item was misreported.

In crypto cases, I see two recurring patterns. One is the taxpayer who could not file because an exchange failed and records were unavailable for a period. The other is the taxpayer who simply did not know how to compute years of trades and froze. The first can support reasonable cause if the records problem was real and the taxpayer acted promptly once records were available. The second usually does not, because difficulty is not the same as inability.

Either way, the record you build is the same kind of record: what happened, when, what you did about it, and documents that prove each step.

What does not work

Some arguments almost never succeed.

  • “I didn’t know crypto was taxable.” The IRS has said virtual currency is property since Notice 2014-21. IRM 25.1.2.11.2 lists the IRS’s public notices on digital asset reporting and tells IRS personnel to consider them in evaluating reasonable cause.
  • “I got Letter 6173, 6174 or 6174-A and did nothing.” After a letter, misunderstanding is very hard to argue. See what happens after an ignored crypto letter.
  • “I answered ‘No’ to the digital asset question because I didn’t think it applied.” Possible, but the question is direct and the instructions are specific. See the digital asset question.
  • “I was busy.” Example 4 in the regulation describes a taxpayer who procrastinated, rushed the return on April 15, and made errors. No reasonable cause.

Building the record

Reasonable cause is proved with facts and documents. For each year, assemble:

  • What records you had when you filed, and how you gathered them.
  • What you gave your preparer or loaded into software, and when.
  • Any professional advice you received, in writing if possible.
  • The specific misunderstanding, if any, and why it was reasonable given your experience.
  • What you did when you learned of the error, including any amended return filed before IRS contact.

Present it per year and per item. Reasonable cause under 6664(c)(1) applies to “any portion” of an underpayment, so you can win it for some items and not others.

Do not forget the procedural defenses

Reasonable cause is a merits defense. Run the procedural checks alongside it. Did the IRS obtain timely written supervisory approval under IRC 6751(b) for penalties that need it? In court, has the IRS met its burden of production under IRC 7491(c)? See supervisory approval of crypto penalties and the burden of proof in crypto cases.

The law requires prudence and care, not perfection. Show the IRS the prudence and the care, with paper, and a lot of crypto penalties go away.