What are the penalties if you miss the Self Assessment tax return deadline?

29 January 2026 | posted in Self Assessment tax returns

What happens if you miss the Self Assessment tax return deadline?

You’ll get a penalty if you need to complete a Self Assessment tax return and you miss the 31 January deadline.

The tax return filing deadline for the tax year ended 5 April 2025 is Saturday 31 January 2026. If you need to complete a Self Assessment tax return and you file late, it’s an automatic £100 penalty regardless of whether you owe any tax or not.

If you leave it longer, penalties can really start stacking up – daily penalties of £10 a day can apply if the return is more than three months late (up to a maximum of £900). Leave it longer than that, and percentage penalties apply on top of that too.

After six months, you’ll get a further penalty of 5% of the tax due or £300 (whichever is greater) and if you’re more than 12 months late, there’s another 5% or £300 penalty (again, whichever is greater).

If you’re part of a partnership, all partners will be charged a penalty if the partnership tax return is late.

Penalties for late payment of tax

There are further penalties if the tax liability itself is paid late. Any tax owed must be paid by 31 January 2026. (There is a second payment deadline of 31 July if you make payments on account. These are payments made towards your next tax bill which help spread  the cost of your tax by making payments in two instalments with each payment being half of the tax you owed last year.)

Interest gets applied from day one and penalties can apply beyond that the longer the balance is unpaid. There are penalties of 5% of the unpaid tax after 30 days, six months and 12 months.

These charges can grow faster than you would expect, so please don’t make your tax situation worse – get your tax return dealt with as soon as possible. If you aren’t sure exactly how much you owe, paying an estimated amount could reduce the penalties you’re charged.

If you do miss the deadline, you can estimate your penalty for late Self Assessment tax returns and payments on the Gov.UK website.