Reasonable cause is the phrase everyone uses and almost nobody defines. People think it means a good excuse. It does not. It means something narrower, and something you can prove.

The test comes from the regulations. Under Treas. Reg. 301.6651-1(c)(1), a late filing is due to reasonable cause if the taxpayer exercised ordinary business care and prudence and was nevertheless unable to file on time. The Internal Revenue Manual applies the same idea across penalties: relief is generally granted when you exercised ordinary business care and prudence in determining your tax obligations but were nevertheless unable to comply with them. That language is in IRM 20.1.1.3.2.

Two halves. You were careful. Something still stopped you. Miss either half and the request fails.

The law requires prudence, not perfection

IRM 20.1.1.3.2.2 describes ordinary business care and prudence as taking the degree of care a reasonably prudent person would exercise. It includes making provisions for business obligations to be met when reasonably foreseeable events occur.

That last part matters. Foreseeable events are your problem. If your bookkeeper always goes on vacation in April, a careful person plans around it. If your bookkeeper is hit by a car on April 10, nobody planned for that.

The Supreme Court described the burden plainly in United States v. Boyle, 469 U.S. 241 (1985). The taxpayer must prove both that the failure did not result from willful neglect and that it was due to reasonable cause. The Court read willful neglect as a conscious, intentional failure or reckless indifference, and it accepted the regulation's ordinary business care and prudence test for reasonable cause.

The five questions the IRS asks

IRM 20.1.1.3.2 gives IRS employees a set of questions to evaluate every reasonable cause request. If you want to know what your letter has to answer, here it is:

  • What happened and when did it happen?
  • During the period you were noncompliant, what facts and circumstances prevented you from filing, paying or otherwise complying?
  • How did those facts and circumstances result in the noncompliance?
  • How did you handle the rest of your affairs during this time?
  • Once the facts and circumstances changed, what did you do to comply?

Read the fourth question again. It is the one people never see coming. If you were too sick to file your return but you were running your business, signing contracts and taking vacations, the IRS will notice. Your explanation has to account for the whole period, not just the tax piece of it.

Four factors the IRS weighs

IRM 20.1.1.3.2.2 lists four things employees review:

  • Your reason. It has to address the penalty imposed, and the dates and explanations should clearly correspond with the events on which the penalty is based.
  • Your compliance history. The manual says to check at least the three preceding years. The same penalty in the past may suggest you are not exercising ordinary business care. A first offense is weighed with your other reasons, but the manual is explicit that a first failure does not by itself establish reasonable cause.
  • Length of time. When was the act required, how long were you unable to comply, and when did you finally comply?
  • Circumstances beyond your control. Could you have anticipated the event? Your obligation is ongoing, so the manual expects you to keep trying to comply even though late.

If your history is clean, you may not need reasonable cause at all. First-time abatement asks only about your record. Check that first.

Timing decides more cases than anything else

The manual says reasonable cause does not exist if, after the circumstances that explain the noncompliance end, the taxpayer fails to comply within a reasonable period of time.

IRM 20.1.1.3.5 gives two examples of requests that may fail. In one, a death in the family occurred several months before the due date, and the return was not filed until a year after the due date. In the other, records held by a third party were returned well before the deadline, but the return was filed months after they came back.

In both cases the event was real. The problem was the gap. The event explains some of the delay. It does not explain all of it. When the IRS lines up your dates and finds a stretch of months with no explanation, the request usually stops there.

So build a timeline before you write anything. Due date. Event start. Event end. Date you filed or paid. If there is a gap between the event ending and compliance, explain it or expect to lose on it.

What usually works, and what usually does not

The manual walks through the common categories of reasonable cause, and each has its own guide in this library:

The manual also names what usually fails. Claiming a mistake was made is generally not in keeping with ordinary business care and prudence. Forgetfulness is generally not a basis for reasonable cause. Relying on someone else to file or pay is generally not enough, because that responsibility cannot be delegated. More on that in why forgetting is not reasonable cause.

The list is not closed. IRM 20.1.1.3.2 says an acceptable explanation is not limited to the examples in the manual. Any reason that shows ordinary business care and prudence may be considered.

Willful neglect is a separate hurdle

Most penalty statutes that allow this relief use the phrase reasonable cause and not due to willful neglect. IRC 6651(a)(1) and (a)(2) both do. That is two tests, not one.

In practice, the willful neglect half rarely decides ordinary cases, because someone who meets the ordinary business care standard is usually not consciously ignoring the law. But it matters when the record shows the taxpayer knew about the obligation and chose to put it off. A request that admits you saw the notices and set them aside has a willful neglect problem no matter how sympathetic the rest of it is.

The manual also tells employees that reasonable cause should never be presumed. The explanation has to come from you, and it has to be supported.

A note on sympathy

IRS employees are people, and a hard story can be moving. But the request is decided against written criteria, often with the help of the Reasonable Cause Assistant software the manual requires employees to use for many failure-to-file, failure-to-pay and deposit penalty requests. Sympathy that is not tied to the criteria does not move the result.

Write for the criteria. Let the facts carry the emotion.

Failure to pay is a different question

Do not assume the same facts excuse a late payment. The regulation treats them differently. Under Treas. Reg. 301.6651-1(c)(1), a failure to pay is due to reasonable cause to the extent you show you exercised ordinary business care and prudence in providing for payment and were nevertheless unable to pay, or would suffer an undue hardship if you paid on the due date.

The regulation then gives examples of what is not prudent: lavish or extravagant living expenses that leave too little to pay the tax, and putting money into speculative or illiquid assets without enough left over. The full analysis is in failure-to-pay penalty relief and undue hardship.

The request itself

The regulation says a taxpayer seeking to avoid the failure-to-file or failure-to-pay addition must make an affirmative showing of all facts alleged as reasonable cause in a written statement containing a declaration that it is made under penalties of perjury. The IRS can consider oral requests in some situations, but a signed written statement is the formal standard and the safer course.

Your statement should identify each penalty and tax period, tell the story in date order, attach proof, and end by showing how quickly you complied once you could. I walk through structure in writing a penalty abatement letter. For how the firm approaches these requests, see penalty abatement at getirshelp.com.

The burden is on you. The manual says so. Meet it with dates and documents, not adjectives.