Self Assessment registration deadline (5 October)

Anyone who needs to file a Self Assessment return for the first time must register with HMRC by 5 October following the end of the tax year (5 April) in which the trading started.

What is this filing?

The 5 October registration deadline applies to new self-employed individuals, new landlords, those starting to receive untaxed income, and high earners newly within scope (e.g. £100k+ income, child benefit clawback). Registration generates a UTR which is required to file the SA100.

When is it due?

5 October following the end of the tax year in which the obligation arose. E.g. someone who started trading on 1 June 2026 (in the 2026–27 tax year) must register by 5 October 2027.

What's the penalty for missing it?

Failure to register on time is treated as failure to notify chargeability. Penalties are based on the 'potential lost revenue' (PLR) and range from 0% (unprompted disclosure, reasonable excuse) up to 100% of the tax due for deliberate and concealed cases.

How PenaltyProof helps

PenaltyProof's Self Assessment secondary-date alerts cover the 5 October registration deadline at practice level (paid plans).

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