A reasonable-cause letter that wins is short, specific, and chronologically tight. A letter that loses is vague, argumentative, or asserts events without documents. The single best predictor of approval is whether the IRS examiner — who has 100 of these on their desk — can read the letter in under three minutes and understand exactly what happened, when, and why it prevented compliance.
The six-section structure
1. Identification
Open with the taxpayer name, EIN/SSN, tax form and year, and the specific penalty being challenged with its IRC section. One paragraph.
2. The standard
State the legal standard you are invoking — reasonable cause under IRC §6651(a) or the relevant section — and cite IRM 20.1.1 or the applicable regulation. Two sentences.
3. The facts (timeline)
Lay out the events chronologically, with specific dates. Start with the taxpayer's normal compliance process. Identify the triggering event. Describe how it unfolded. End with the corrective action and the filing date. This section is most of the letter — typically 60% of the total length.
4. Causation
Explicitly tie the event to the compliance failure. The IRS reviewer needs to see why the event prevented timely filing or payment — not just that it happened during the same period. "The medical incident on March 10 left the responsible officer hospitalized through May 2; the return was due April 15; the corporate records were in her exclusive custody and inaccessible during the hospitalization."
5. Corrective action
What did the taxpayer do once the obstacle resolved? How quickly? Demonstrating prompt action after the event is part of the "ordinary business care and prudence" showing.
6. Attached documents
List the exhibits attached to the letter — medical records, death certificates, FEMA notices, third-party correspondence — labeled as Exhibit A, B, C, etc. The letter references the exhibits inline.
Three things the examiner needs to see, in order: (1) specificity — exact dates and named events, not "around March I had some issues"; (2) substantiation — every asserted fact should have a document behind it; (3) continuity — the chain from event to non-compliance must be unbroken, covering the entire delinquency period.
Common drafting failures
- Vague timing. "Around tax time" or "during 2020" instead of specific dates.
- Asserting without proving. Claiming records were destroyed but not attaching an insurance claim or police report.
- Addressing only the start of the period. Explaining why March was hard but not why the return was eventually filed in November.
- Arguing instead of stating. Long passages of policy arguments rather than facts.
- Multiple grounds in conflict. Claiming both "I forgot" and "I was incapacitated" — they cannot both be true and the inconsistency damages credibility.
The signature
The letter and Form 843 must be wet-signed — Form 843 cannot be e-filed and cannot be submitted with an electronic signature. The taxpayer signs personally for individual returns; for entities, an authorized officer signs. If a representative (CPA, EA, or attorney) is signing under a Form 2848 power of attorney, that authorization must be on file or attached.
Templates you can adapt
We have published five reasonable-cause letter templates covering the most common scenarios — serious illness, natural disaster, records destruction, advisor error, and prolonged inability to obtain third-party records. Each is annotated with the IRS standard each section addresses. See letter examples.