A "reasonable excuse" is the legal mechanism through which HMRC can cancel a late filing penalty. If you had a genuine reason — beyond your control — that prevented you from filing on time, you may be able to get the penalty reduced or cancelled entirely through a formal appeal.
The problem is that HMRC applies a specific legal test to these appeals. The excuse has to be genuine, it has to have actually prevented filing (not just made it difficult), and you have to have acted promptly once the preventing circumstances resolved. Thousands of appeals are rejected every year because they fail one of these three tests.
The Three-Part Test HMRC Applies to Every Appeal
Before getting into what qualifies, understand the test. All three elements must be satisfied:
- 1The circumstances were genuinely beyond your reasonable control — you did not choose them and could not have predicted them.
- 2Those circumstances actually prevented you from filing — not just made it inconvenient or difficult, but genuinely impossible or unreasonable to expect.
- 3You acted promptly once those circumstances resolved — you did not leave it weeks or months before filing once you were able to.
The third point catches a significant proportion of otherwise-valid appeals. Someone who had a serious illness is in a strong position — until HMRC notices that they recovered in June but did not file until the following January. That delay, unexplained, undermines the entire appeal.
Excuses HMRC Accepts
Serious Illness — Yours or a Close Relative's
A serious illness that genuinely incapacitated you — or that required you to be a full-time carer for someone with no other support — is the most commonly accepted excuse. The threshold is real incapacity, not feeling unwell. Hospital admissions, major surgery, mental health crises requiring clinical intervention, and terminal diagnoses all qualify. A fortnight of flu does not.
Evidence needed: a letter from a GP or hospital confirming the diagnosis, the dates of incapacity, and that you were unable to manage administrative affairs during the relevant period. The more specific the dates relative to the 31 January deadline, the stronger the appeal.
Bereavement of a Close Relative
The death of a spouse, partner, parent, child, or sibling close to the filing deadline is accepted. "Close to" is interpreted generously where the bereavement is genuinely recent — a death in December or January is significantly easier to argue than one the previous spring. Estate administration responsibilities on top of grief strengthen the argument further.
Evidence needed: death certificate. A GP letter confirming your state during the period is helpful but not always required.
HMRC or Government System Failure
If HMRC's own online filing system was unavailable at a critical time — for example, a confirmed outage on 31 January — this is accepted without question. HMRC publishes records of system failures and they cannot reasonably penalise taxpayers for their own infrastructure problems. Screenshot evidence of the error, dated, is ideal.
Fire, Flood, Theft, or Natural Disaster
Where a physical event destroyed or made inaccessible the records you needed to complete the return, and that event happened close enough to the deadline to have genuinely prevented filing, this qualifies. Police crime reference numbers, insurance claims, fire brigade reports, and photographs all serve as evidence.
Emergency Hospital Admission
An unplanned emergency admission — yours or that of a person entirely in your care — that overlaps with the period leading up to the deadline is accepted. Planned procedures are harder to argue because you had advance notice; emergency admissions are straightforwardly beyond your control.
Excuses HMRC Always Rejects
These will not succeed at appeal — ever
The following excuses have been tested at tax tribunal repeatedly. They have lost, consistently. Do not build an appeal around any of them.
- Being too busy — work pressure, business demands, and staffing problems are explicitly excluded in HMRC guidance. No tribunal has ever accepted this.
- Not knowing about the filing obligation — awareness of Self Assessment requirements is considered the taxpayer's responsibility.
- Your accountant failed to file — the general rule is that agent failure is the taxpayer's problem, not a reasonable excuse. (Some very specific exceptions exist, but they are narrow.)
- Forgetting the deadline — this has never succeeded at tribunal.
- Finding the return too complicated — complexity of your affairs does not excuse lateness. You are expected to get help.
- Not having the money to pay — inability to pay the tax owed does not excuse the failure to file the return itself.
- Waiting for missing documents from a third party — you can file on estimated figures and amend later.
Why DIY Appeals Fail
HMRC's penalty appeals team processes thousands of letters a month. A letter that says "I was ill" without specifying dates, attaching medical evidence, or explaining why the delay after recovery was reasonable will be rejected. A letter that cites an accepted excuse but fails to demonstrate that it actually prevented filing — rather than making it inconvenient — will be rejected.
The structure of an appeal matters as much as the content. A specialist who handles these cases regularly knows how HMRC frames the three-part test in practice, which evidence is considered compelling versus marginal, and how to present the timeline in a way that addresses HMRC's likely objections in advance.
You also cannot appeal until the return is actually filed. HMRC will not consider a penalty appeal for an outstanding return. Filing comes first — then appeal.
HMRC rejects thousands of DIY appeals — don't be one of them
Our tax agents draft and submit penalty appeals for you. We assess whether your excuse qualifies before we start, so you know the realistic outcome upfront. No fee for the assessment.