Missing a self-assessment deadline means an automatic fine from HMRC — even if you don't owe a penny in tax. Here are the dates every sole trader and subcontractor needs in the diary.

The deadlines that matter

  • 5 October — deadline to register for self-assessment if you're newly self-employed
  • 31 October — deadline for paper tax returns
  • 31 January — deadline for online tax returns, and to pay any tax you owe
  • 31 July — second "payment on account" deadline, if applicable

💡 Quick tip: Almost everyone files online now, so 31 January is the date to burn into your memory. It's both the filing deadline and the payment deadline.

What the penalties look like

Miss the 31 January online deadline and here's what HMRC charges:

  • £100 immediately — even if you owe no tax or are due a refund
  • After 3 months — £10 per day, up to £900
  • After 6 months — a further penalty on top
  • Interest is also charged on any tax paid late

Those fines stack up fast, which is why filing early is always the cheaper option.

What "payments on account" means

If your tax bill is over £1,000, HMRC asks you to pay next year's tax in two advance instalments — one on 31 January, one on 31 July. It catches a lot of people out in their first year, because it can feel like you're paying "one and a half times" your bill. You're not — you're just paying some of it early.

Don't leave it to January

The single best habit is to get your records to your accountant well before Christmas. The January rush is when mistakes happen, HMRC's systems get slow, and stress peaks. File early, know your number, and pay on time.

Topics: Self-Assessment Tax Deadlines Sole Traders