There are penalties for late filing of a Self Assessment tax return in the UK, as follows:
If you miss the deadline for online submission (31 January following the end of the tax year), you will be charged an initial penalty of £100.
If your tax return is still outstanding after three months (i.e. by 30 April), you will be charged an additional daily penalty of £10 per day, up to a maximum of £900.
After six months (i.e. by 31 July), you will be charged a further penalty of 5% of the tax due or £300 (whichever is greater).
If your tax return is still outstanding after 12 months (i.e. by 31 January of the following year), you will be charged a further penalty of 5% of the tax due or £300 (whichever is greater).
Note that the penalties apply even if you have no tax to pay or have already paid all the tax you owe. It's therefore important to file your tax return on time, or as soon as possible after the deadline, to avoid these penalties.
