Written by the TaxTune Editorial Team · Reviewed by our qualified accountants · Updated for 2026
The quick answer The key dates are 5 October to register, 31 October for a paper return, and 31 January to file online and pay. Miss the online filing deadline and there is an automatic £100 penalty even if no tax is due, followed by daily penalties after 3 months.

The deadlines that matter

  1. 5 October. Register for Self Assessment if this is your first year.
  2. 31 October. Deadline for a paper return.
  3. 31 January. Deadline to file online and to pay the tax you owe, plus any first payment on account.
  4. 31 July. Second payment on account, if you make them.

What late filing costs

  • The moment you miss 31 January: an automatic £100 penalty, even if no tax is due.
  • After 3 months: £10 a day for up to 90 days, a further £900.
  • After 6 months: the greater of 5% of the tax due or £300.
  • After 12 months: another 5% or £300, and more in serious cases.

What late payment costs

Interest runs from 1 February on anything unpaid. On top of that, HMRC adds a 5% surcharge on tax still unpaid after 30 days, again after 6 months, and again after 12 months. Filing on time but paying late still triggers these.

Already had a penalty?

If a fine has landed, there may be grounds to appeal, and there is often relief you have missed. TaxTune can review it, appeal where there is a reasonable excuse, and make sure it never happens again.

How to appeal a penaltyAsk for help

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Frequently asked questions

What is the Self Assessment deadline?

You must file online and pay any tax you owe by 31 January following the end of the tax year. A paper return is due earlier, by 31 October, and first year registration by 5 October.

What is the penalty for filing late?

An automatic £100 the moment you miss 31 January, then £10 a day after 3 months up to £900, then the greater of 5% of the tax or £300 at 6 and 12 months.

What if I pay late but file on time?

Interest runs from 1 February, and HMRC adds a 5% surcharge on tax unpaid after 30 days, 6 months and 12 months. Filing on time does not stop late payment penalties.

Can I appeal a penalty?

Yes, if you have a reasonable excuse such as serious illness or bereavement. You appeal to HMRC, ideally with evidence, and the penalty can be cancelled.

Is there a penalty if no tax is due?

Yes. The £100 late filing penalty applies even when your tax bill is zero, as long as HMRC has asked you to file a return.