Self Assessment Penalty Calculator, 2026/27

How this is calculated

The self-assessment late filing penalty regime is entirely separate from late payment penalties and applies purely because the return itself was not submitted on time. A fixed £100 penalty applies the day after the 31 January deadline, even where no tax is actually owed or a refund is due.

If the return is still outstanding 3 months later, HMRC can charge daily penalties of £10 a day for up to 90 days, a maximum of £900. At 6 months, a further penalty of the greater of £300 or 5% of the tax due is charged, and the same again at 12 months, meaning a return over a year late can attract penalties well over £1,600 even on a modest tax bill.

These penalties stack on top of each other rather than replacing one another, so the total shown here adds the fixed penalty, any daily penalties, and the 6 and 12 month charges together.

Filing versus paying

This calculator covers only the penalty for filing the return late. Paying the tax itself late triggers a different set of penalties and daily interest, covered separately by the personal tax penalty calculator elsewhere on this site, and both can apply at once if a return is both late and unpaid.

It is possible to owe nothing but still face the full filing penalty regime, which surprises many people who assume no tax due means no penalty risk.

Appeals and reasonable excuse

HMRC will consider cancelling a penalty where there is a reasonable excuse, such as a serious illness, bereavement or system failure at HMRC itself, provided the return is filed as soon as the excuse no longer applies. Simply forgetting, or being too busy, is not normally accepted.

Appeals must usually be made within 30 days of the penalty notice, in writing or online, explaining the reason for the delay and providing supporting evidence where available.

What is the penalty for filing a self-assessment return one day late?

A fixed £100 penalty applies immediately the day after the 31 January deadline, whether or not any tax is actually owed.

What happens if my return is 6 months late?

A further penalty of the greater of £300 or 5% of the tax due is added on top of the earlier fixed and daily penalties, and the same again if it reaches 12 months late.

Are daily penalties automatic?

HMRC can charge £10 a day once a return is 3 months late, for up to 90 days, but this requires HMRC to actually issue the daily penalty notice, which does not always happen immediately.

Can a late filing penalty be appealed?

Yes, if you have a reasonable excuse such as serious illness, bereavement or an HMRC system failure, and you file the return promptly once the excuse ends, usually within 30 days of the penalty notice.