Missing the Self Assessment deadline is expensive, but it is not a disaster. HMRC charges an automatic £100 penalty the day after the deadline, with steeper fines and interest that grow the longer you wait. This guide shows exactly what you owe, what to do today to stop the charges growing, and how to get a penalty cancelled if you had a genuine reason.
What happens if you miss the Self Assessment deadline?
HMRC charges you an automatic £100 late filing penalty, even if you owe no tax. Separate penalties and daily interest apply to any tax paid late. You also lose nothing by acting fast: filing your return today freezes the filing penalties where they are, and paying the bill or setting up a plan stops further late-payment charges.
The first thing to understand is that HMRC treats late filing and late payment as two separate problems. Filing your return late triggers the late filing penalties, which are a fine for the paperwork being late. Paying the tax late triggers late payment penalties plus interest, which are charged on the money owed. You can be hit by both at once, which is why the bill grows faster than most people expect.
The main deadline for an online return is 31 January following the tax year. Paper returns have an earlier deadline of 31 October. Payment of any tax due, including your balancing payment and any first payment on account, is also due by 31 January. So if you missed the January deadline for the 2024/25 tax year, or you are facing the 31 October 2026 paper deadline for the 2025/26 return, the rules below apply to you.
How much are HMRC’s late filing penalties?
For a late online return, HMRC’s filing penalties build in stages: £100 as soon as you miss the deadline, £10 a day from three months late up to £900, then £300 or 5% of the tax due (whichever is greater) at six months, and the same again at twelve months. They stop growing the moment you file.
| How late the return is | Penalty |
|---|---|
| 1 day late | £100 fixed penalty, automatic, even if you owe nothing |
| 3 months late | £10 per day on top of the £100, for up to 90 days (maximum £900) |
| 6 months late | A further £300, or 5% of the tax due, whichever is greater |
| 12 months late | Another £300, or 5% of the tax due, whichever is greater |
Left unfiled for a full year, a single return can attract £1,600 or more in filing penalties alone, before any of the actual tax. This is the schedule published on GOV.UK’s Self Assessment penalties page, so these figures are the official ones.
Watch out: the £100 penalty applies even if your tax bill is £0 or you are due a refund. It is a fine for the return being late, not for tax being unpaid. Filing a nil return late still costs you.
What does paying late cost on top?
Paying your tax bill late is penalised separately from filing late, and it starts with interest from day one. HMRC charges interest daily on any unpaid tax from the day after it was due until you pay in full. The rate tracks the Bank of England base rate plus 4%, and stood at 7.75% a year from 9 January 2026. On top of interest, HMRC adds three late payment penalties: 5% of the tax still unpaid at 30 days late, another 5% at 6 months late, and another 5% at 12 months late.
Here is what that looks like with real numbers. Suppose your Self Assessment bill for 2024/25 is £6,500. You missed the 31 January 2026 deadline, you file the return on 5 June, and you pay nothing until that day. Assumptions: the bill is unpaid for 124 days, the interest rate is 7.75% throughout, and the tax year is 2024/25.
Filing penalties. The £100 fixed penalty applies from 1 February. Daily penalties begin at three months late (1 May). From 1 May to 5 June is 35 days at £10 a day, which is £350. Total filing penalties: £100 + £350 = £450.
Late payment penalties. At 30 days late (2 March), 5% of £6,500 is £325. The 6-month surcharge has not been reached. Total late payment penalties: £325.
Interest. £6,500 x 7.75% x 124/365 = £171. So the cost of the delay is £450 + £325 + £171 = £946, on top of the £6,500 bill. And if you still had not paid by August, another 5% surcharge would land.
A useful rule of thumb: file on time even when you cannot pay. Filing on time removes the entire filing-penalty column from the example above, leaving only the payment penalties and interest to deal with.
What should you do right now if you have missed it?
Work through these steps in order. Each one stops a different set of charges from growing.
1. File the return today. The moment your return is submitted, the filing penalties freeze. No more daily £10 charges, and the 6-month and 12-month percentage penalties never trigger. File online if you can, as paper returns are already past their deadline for the current tax year.
2. Pay what you can immediately. Every pound you pay now reduces the balance that interest and the future 5% surcharges are calculated on. If you cannot pay in full, pay part of it. Do not wait until you can clear the whole bill.
3. Set up a Time to Pay arrangement. If you owe £30,000 or less and have no other tax debts, you can usually set up a payment plan online through your HMRC account. This spreads the bill over monthly instalments and prevents the later 5% surcharges, though interest keeps running while you pay.
4. Check the penalty notice. HMRC sends penalty notices to the address they hold for you. Make sure your personal details and bank details are current in your HMRC online account so notices and any refunds reach you.
Tip: the biggest avoidable cost is paperwork chaos. Keeping clean records through the year makes January filing trivial. LancerBill’s invoice generator gives you a free, properly numbered trail of every invoice you issued, which is half the work of a Self Assessment return. See also our step-by-step on how to write an invoice if your records are patchy.
Can HMRC cancel a Self Assessment penalty?
Yes, HMRC can cancel a penalty if you have a ‘reasonable excuse’, meaning an event genuinely beyond your control such as serious illness, bereavement or a system failure. You must appeal within 30 days of the penalty notice, explain what happened and provide evidence. Being busy or forgetting does not count.
You can appeal online through your HMRC account, by post, or in some cases through the HMRC app. In your appeal, say which penalty you are challenging, give the date and reference on the penalty notice, explain the excuse in plain terms, and attach whatever evidence you have. HMRC’s own examples of reasonable excuses include a close bereavement shortly before the deadline, unexpected hospital treatment, a fire or flood destroying records, and failures in HMRC’s own online service.
Excuses that almost never work include being too busy, not knowing you had to file, relying on an accountant who let you down, or money problems stopping you from paying. If your appeal is rejected, you can ask HMRC to review the decision, and after that take it to a tax tribunal.
Watch out: interest on unpaid tax cannot be appealed away. Unlike penalties, interest is not a punishment, it is the cost of holding money that belonged to HMRC, and there is no reasonable-excuse defence against it.
How to never miss the deadline again
A simple system beats good intentions. Mark the key dates now: 5 October to register for Self Assessment in your first year, 31 October for paper returns, and 31 January for the online return plus all tax payments. Set a personal deadline at least two weeks before each of these, so technical glitches and missing paperwork cannot hurt you.
Start the return in autumn rather than January. You can open it online, save it, and come back as many times as you like before submitting. If you do any VAT-registered work, watch the £90,000 registration threshold too, which our guide on whether freelancers need to charge VAT covers, and use a VAT calculator to keep your figures exact.
Finally, make sure your rates actually leave room for the tax bill. Many freelancers miss deadlines partly because the bill itself feels unmanageable. Running your numbers through a profit margin calculator each quarter keeps your pricing honest and leaves the money set aside before HMRC comes asking.
Rates last reviewed: October 2026. Penalties and interest rates are set by HMRC and move with the Bank of England base rate, so confirm the current figures on GOV.UK before relying on them.
Key takeaways
- The £100 late filing penalty is automatic, even if you owe no tax. Daily £10 charges start at three months, with 5% or £300 penalties at six and twelve months.
- Paying late is penalised separately: 5% surcharges at 30 days, 6 months and 12 months, plus daily interest (7.75% from 9 January 2026).
- Filing today freezes the filing penalties immediately, even before you can pay the bill.
- A Time to Pay arrangement stops the later payment surcharges while you clear the debt in instalments.
- HMRC can cancel penalties for a genuine reasonable excuse, appealed within 30 days of the notice, but interest cannot be appealed.
- Filing on time and paying late is always cheaper than doing both late.
Self Assessment is also changing: our guide to Making Tax Digital for Income Tax 2026 explains the 50,000 pound threshold, the quarterly deadlines and what sole traders must file.
To avoid a bill you cannot pay, our guide on how much tax a self-employed person should set aside gives a percentage for each profit level.
Frequently asked questions
Do I get a penalty if I miss the Self Assessment deadline but owe no tax?
Yes. The £100 late filing penalty applies automatically whether you owe tax or not. It is a fine for the return being late, not for the tax being unpaid. If you file a nil return three months late, you also face the £10-a-day charges. Filing on time costs nothing, so there is no reason to skip it.
What is a reasonable excuse for missing the Self Assessment deadline?
A reasonable excuse is an unexpected event genuinely beyond your control, such as serious illness, a close bereavement shortly before the deadline, a fire or flood destroying your records, or a failure in HMRC’s own systems. Being busy, forgetting, or your accountant letting you down do not count. You must appeal within 30 days of the penalty notice with evidence.
Does filing my return stop the penalties if I still cannot pay?
Filing stops the late filing penalties from growing, which is why it should always come first. The late payment penalties and daily interest on unpaid tax continue separately until you pay or set up a Time to Pay plan. Filing on time but paying late is always cheaper than doing both late.
How do I set up a Time to Pay arrangement with HMRC?
If you owe £30,000 or less with no other tax debts, you can usually set up a payment plan online through your HMRC account. The plan spreads the bill over monthly instalments and stops the future 5% late payment surcharges, though interest keeps accruing. Contact HMRC before the surcharges escalate for the best result.
What is the Self Assessment deadline for the 2025/26 tax year?
For the tax year that ended on 5 April 2026, paper returns are due by 31 October 2026 and online returns by 31 January 2027. All tax due, including the balancing payment and first payment on account, is due by 31 January 2027. If you miss the paper deadline, you can still file online by 31 January without a penalty.
Can I appeal a Self Assessment penalty after 30 days?
The 30-day appeal window starts from the date on the penalty notice, not when it arrives. If you miss it, you can still appeal but you must explain the late appeal too, and HMRC is not obliged to accept it. Act on the notice the day it arrives.
Filing late is easier to avoid when the bill holds no surprises: our guide to calculating self-employed tax step by step shows the full 2026/27 calculation before you file.
This guide is for general information only and is not financial, tax or legal advice.