What are the UK Self Assessment deadlines and late filing penalty structures?

Guide to Self Assessment Milestones, Payments on Account, and Late Filing Penalties

If you are a sole trader, partner, director, or high-income individual earning over certain limits in the UK, you must report personal income via the Self Assessment system.

1. Core Compliance Dates

The UK tax year runs from 6 April to 5 April. Mark these critical milestones on your financial calendar:

2. The Penalty Matrix for Late Submission

HMRC maintains a highly strict, automatic fine schedule for late submissions, even if you do not owe any tax:

1. 1 Day Late: An immediate, automatic flat penalty of £100.

2. Up to 3 Months Late: Compounding penalties of £10 per day (capped at £900 for up to 90 days).

3. 6 Months Late: Further penalty of 5% of the tax due or £300 (whichever is greater).

4. 12 Months Late: An additional penalty of 5% of the tax due or £300 (whichever is greater), with possible higher fines if HMRC suspects deliberate concealment.

3. Surcharges on Late Payments

Separately from the filing deadline, late payments of the tax itself incur compounding interest (the current bank base rate + 2.5%) and flat surcharges:

4. Payments on Account

If your Self Assessment tax liability exceeds £1,000 (and less than 80% is collected at source like PAYE), you are automatically enrolled in Payments on Account.