Late Self Assessment tax returns and penalty appeals
If you have missed the Self Assessment deadline, file the return as soon as you can, because HMRC’s late filing penalties grow the longer it stays outstanding. IB&Co Accountants, accountants and tax advisers in Canary Wharf, can prepare and file your late return, check every penalty and appeal any that you have a reasonable excuse for.
What happens if I miss the Self Assessment deadline?
HMRC must receive an online tax return by 11:59pm on 31 January after the end of the tax year, and a paper return by 31 October. For the 2025 to 2026 tax year, that means 31 October 2026 for paper and 31 January 2027 online. Any tax you owe is also due by 31 January.
If you miss the filing deadline, HMRC charges late filing penalties that build up over time:
- an initial £100 penalty, even if you have no tax to pay or you pay on time
- after 3 months, £10 for each day, up to a maximum of £900
- after 6 months, a further 5% of the tax due or £300, whichever is greater
- after 12 months, another 5% of the tax due or £300, whichever is greater
Paying late is a separate problem. HMRC charges a penalty of 5% of the tax still unpaid at 30 days, at 6 months and at 12 months, and charges interest on the amount owed from the day after the deadline. Late payment interest is set at the Bank of England base rate plus 4%.
I have not registered for Self Assessment yet. Is it too late?
No, but act now. You must tell HMRC by 5 October if you need to file a return for the previous tax year. If you register after 5 October 2026, HMRC will give you a filing deadline 3 months from the date of its letter or email, but the tax is still due by 31 January 2027. If you register late and do not pay in full by 31 January, you may get a separate “failure to notify” penalty.
We can register you, get your Unique Taxpayer Reference moving and prepare the return in parallel, so you are ready to file as soon as HMRC’s letter arrives. See our Tax Registration with HMRC service.
How do I sort out a late tax return?
There are four steps, and the order matters.
- Find out what is outstanding. We check which years HMRC expects returns for and what penalties have been charged so far.
- Gather your records. Bank statements, invoices, P60s, rental statements and receipts. If records are missing, we help you rebuild reasonable figures and explain how they were reached.
- File the return. Filing stops the daily penalties growing, so we prioritise getting a complete and accurate return submitted.
- Deal with the bill. If you cannot pay in full, HMRC may agree a payment plan, often called a Time to Pay arrangement. It is best to contact HMRC as soon as you know you cannot pay.
If more than one year is late, we deal with the oldest return first, because its penalties are usually the largest.
Can I appeal a late filing penalty?
Yes, if you have a reasonable excuse. You usually have 30 days from the date the penalty was issued to contact HMRC or appeal. HMRC’s own examples of a reasonable excuse include the death of a partner or close relative shortly before the deadline, an unexpected stay in hospital, a serious or life-threatening illness, a computer or software failure while preparing your online return, and a fire, flood or theft that stopped you completing the return.
HMRC says it will not accept these as a reasonable excuse: a payment that failed because there was not enough money, finding the online system too difficult, not getting a reminder, or making a mistake on your return.
You can appeal online or by post. HMRC suggests you consider paying the penalty while the appeal is decided: if you do not pay and the appeal fails, interest runs on the penalty, and if the appeal succeeds HMRC repays it with interest, as long as you have no other tax to pay. We prepare the appeal, set out the facts and dates clearly, and handle HMRC’s reply as your agent.
Does Making Tax Digital change the penalties?
If you have to use Making Tax Digital for Income Tax from 6 April 2026, new penalties apply from the 2026 to 2027 tax year. Late submissions earn points instead of the £100 and daily penalties, with a £200 penalty at 4 points, and late payment penalties are worked out on how late you pay. Your 2025 to 2026 tax return, due by 31 January 2027, is still covered by the penalties above. For 2026 to 2027, late quarterly updates do not earn points, but a late tax return still does. The government announced at the Budget on 28 October 2026 that people who must join in April 2027 will not get points for late quarterly updates in 2027 to 2028. This is a proposal until it becomes law. Our Making Tax Digital page explains who is affected and when.
Why ask an accountant to file a late return?
Late returns are often late for a reason: missing paperwork, a change in circumstances or a previous adviser who stopped replying. We work around that. One of our clients, a registered nurse, told us her previous accountant had left her “fined by the taxman” before we helped her put things right (see our testimonials).
When you work with IB&Co you get:
- a clear list of what is outstanding and what each penalty is for
- returns prepared from your records and filed as your authorised agent
- a written appeal where you have a reasonable excuse
- help agreeing a payment plan with HMRC if you need one
- a plan so next year’s return is filed on time
The practice is led by Ishmael Bangura FFA. If HMRC has opened an enquiry rather than just charged penalties, see our Tax Investigation Support page.
Frequently asked questions
HMRC charges £100 as soon as the return is late. After 3 months it adds £10 a day for up to 90 days (a maximum of £900). After 6 months and again after 12 months it charges 5% of the tax due or £300, whichever is greater.
Usually yes. The initial £100 late filing penalty applies even if there is no tax to pay. If you did not need to send a return at all, you can ask HMRC to cancel the penalty.
You usually have 30 days from the date the penalty was issued. If you miss that, you need to give a reason for the delay.
Yes. We work out which years are outstanding, start with the oldest, and file each one as your agent. Where records are incomplete, we explain how the figures were reached.
You may be able to set up a payment plan with HMRC, known as Time to Pay. Interest still runs on the unpaid tax, so it helps to agree a plan early. We can help you prepare the figures before you speak to HMRC.
We agree the scope of work with you after a Discovery Call and send you a written proposal before any work starts. The proposal depends on how many years are outstanding and the state of your records.
Get your late return filed
Book a Discovery Call and we will look at what is outstanding and the quickest way to put it right.
Call 020 7164 0225 or visit us at Level 37, 1 Canada Square, Canary Wharf, London E14 5AA. Open Monday to Friday 9:00 to 18:30 and Saturday 10:30 to 16:30.
Checked on 11 November 2026. This page is general information based on HMRC guidance at that date, and is not advice for your circumstances.
