What Happens If I Missed the Self Assessment Deadline?
Missing the Self Assessment deadline can feel stressful, but it is important not to ignore it. The sooner you act, the easier it is to reduce extra costs and avoid the problem getting worse.
In most cases, if you miss the online Self Assessment deadline, HMRC will issue an automatic £100 late filing penalty. This can apply even if you do not owe any tax or your tax bill has already been paid. Further penalties and interest can also build up if your tax return or payment remains outstanding.
The best thing to do is simple: file your tax return as soon as possible and pay what you can. If you cannot pay the full amount straight away, you may still have options.
When Is the Self Assessment Deadline?
For most people, the online Self Assessment tax return deadline is 31 January after the end of the tax year. This is also the date by which any tax owed usually needs to be paid.
For example, for the 2025/26 tax year, which ends on 5 April 2026, the online tax return deadline is 31 January 2027. HMRC states that online returns must be submitted by 11:59pm on 31 January.
Paper tax returns have an earlier deadline, which is usually 31 October.
What Penalties Could I Face?
If your tax return is late, HMRC may charge penalties based on how late it is.
The current late filing penalties are:
- 1 day late: £100 fixed penalty.
- 3 months late: £10 per day, up to a maximum of £900.
- 6 months late: 5% of the tax due or £300, whichever is higher.
- 12 months late: a further 5% of the tax due or £300, whichever is higher.
These charges can add up quickly, which is why it is better to submit your return even if you cannot pay the full tax bill yet.
What If I Have Missed the Payment Deadline Too?
Filing late and paying late are two separate issues. You may receive a penalty for sending your return late and another charge if your tax payment is overdue.
HMRC can also charge interest on late payments. This means the longer the tax remains unpaid, the more the final amount may increase. Penalties may also apply if the tax is still unpaid after 30 days, 6 months and 12 months.
If you cannot afford to pay your bill in full, do not wait until HMRC contacts you. It is usually better to speak to HMRC early and explain your situation.
Can I Set Up a Payment Plan?
If you cannot pay your Self Assessment bill in one go, you may be able to set up a Time to Pay arrangement with HMRC. This allows you to spread the cost over a set period.
You will normally still need to file your tax return first, so HMRC knows how much you owe. Once the return is complete, you can look at your payment options.
A payment plan can help you manage the debt and may prevent further action, as long as you keep to the agreed payments.
Can I Appeal a Self Assessment Penalty?
You may be able to appeal a penalty if you have a reasonable excuse for missing the deadline. HMRC gives examples such as serious illness, bereavement, service issues, or other events that made it impossible for you to file on time.
However, not every excuse will be accepted. Forgetting the deadline, being too busy, or not having the money to pay are usually not enough on their own.
If you appeal, you should explain clearly what happened, when it happened, and why it stopped you from filing or paying on time. You should also submit your tax return as soon as you can.
What Should I Do Now?
If you have missed the Self Assessment deadline, take these steps:
- File your tax return as soon as possible.
This helps stop further late filing penalties from building up. - Pay what you can.
Even a partial payment may reduce the amount of interest charged. - Contact HMRC if you cannot pay in full.
You may be able to agree a payment plan. - Check whether you can appeal.
If you had a genuine reason for missing the deadline, you may be able to challenge the penalty. - Get help if you are unsure.
An accountant can review your position, prepare your return and help you deal with HMRC.
How an Accountant Can Help
An accountant can help you bring your Self Assessment up to date quickly and accurately. This is useful if you are unsure what income to include, what expenses you can claim, or how to deal with penalties.
They can also check whether your tax bill is correct, help you avoid further mistakes and support you with HMRC if you need to appeal a penalty or arrange payment.
Missing the deadline is not ideal, but it can be fixed. The key is to act quickly, submit your return and get clear advice if you need support.
