For nearly thirty years, the fines for filing a Company Tax Return late sat untouched. That changed on 1 April 2026, when HMRC doubled the flat-rate penalties for the first time since 1998. If your limited company misses its CT600 deadline, the cost of being late has gone up sharply, and HMRC has confirmed the automatic penalty notices have resumed after a short pause to update its systems.
This guide sets out exactly what the 2026 Corporation Tax late filing penalties are, when they apply, how the repeat-offender rates work, how they stack up against the unpaid tax, and how to appeal if you have a reasonable excuse. Every figure here is taken from live gov.uk guidance. For the mechanics of the return itself, see our guide to the Company Tax Return (CT600) and its filing deadlines.
What are the corporation tax late filing penalties in 2026?
Corporation Tax late filing penalties doubled for returns with a filing date on or after 1 April 2026. A return filed up to three months late now costs £200, rising to £400 once it is more than three months late. On top of that, HMRC adds tax-geared penalties of up to 20% of any unpaid Corporation Tax if the return is six months or more overdue.
The penalties fall into two parts: fixed flat-rate fines that apply however much tax you owe, and tax-geared penalties calculated as a percentage of the Corporation Tax outstanding. Both are set out on the gov.uk late filing penalties page. These penalties are for filing the return late, which is separate from interest charged for paying your Corporation Tax late.
How much have CT600 late filing penalties increased?
The flat-rate penalties have doubled, the first increase since 1998. A first late return rose from £100 to £200, a return more than three months late from £200 to £400, and the penalties for persistent late filing climbed from £500 and £1,000 to £1,000 and £2,000. HMRC says inflation had eroded the old fines to around half their original value in real terms.
The table below compares the old and new flat-rate penalties, taken from HMRC's increases to late filing penalties guidance.
| How late the return is | Penalty before 1 Apr 2026 | Penalty from 1 Apr 2026 |
|---|---|---|
| Up to 3 months late | £100 | £200 |
| More than 3 months late | £200 | £400 |
| Third return in a row, up to 3 months late | £500 | £1,000 |
| Third return in a row, more than 3 months late | £1,000 | £2,000 |
These are the fixed penalties only. Where Corporation Tax is also unpaid, the tax-geared penalties below are charged in addition.
When do the new corporation tax penalties apply?
The higher penalties apply to any Company Tax Return whose filing date falls on or after 1 April 2026. The filing date is normally twelve months after the end of your accounting period, so the first returns caught by the new rates are those for accounting periods ending on or after 1 April 2025. Returns with an earlier filing date keep the old £100 and £200 fines.
In practice, almost every company filing a late return now will be subject to the doubled penalties. If you are unsure which rate applies, work backwards from your accounting period end date, which you can check on your Company Tax Return deadlines.
What is the deadline for filing a Company Tax Return?
You must file your Company Tax Return (CT600) within twelve months of the end of your accounting period. This is separate from the payment deadline, which is usually nine months and one day after the period ends. Missing the filing date is what triggers these penalties, while paying late triggers interest instead.
Confusing the two deadlines is one of the most common and expensive mistakes directors make. You can pay your Corporation Tax before you file the return, and in most cases you have to. See our guide on how and when to pay Corporation Tax and the official pay Corporation Tax guidance for the payment side.
What happens if your return is more than six months late?
Once a return is six months late, HMRC estimates your Corporation Tax bill, issues a tax determination you cannot appeal, and adds a tax-geared penalty of 10% of the unpaid tax. At twelve months late, a further 10% is charged. That is up to 20% of the Corporation Tax owed, on top of the flat-rate fines.
The tax-geared penalties were not changed by the 2026 reform, but because they sit on top of the doubled flat-rate fines, the total bill for a seriously late return is now significantly higher. Late payment also attracts HMRC interest and penalties on the tax itself, which compounds the cost.
What are the penalties for repeated late filing?
If you file late for three accounting periods in a row, the £200 flat-rate penalties increase to £1,000 each. That means £1,000 for a third consecutive return filed within three months of the deadline, or £2,000 if it is more than three months late. These repeat-offender penalties apply separately from any tax-geared penalty on unpaid Corporation Tax.
The higher rate applies where returns for three or more consecutive accounting periods are filed late and the company was liable to penalties for the first two of those periods. Persistent late filing is exactly the behaviour the 2026 increase is designed to deter.
Worked example: how the 2026 penalties add up
Consider a company with an accounting period ending 30 April 2026 and a filing deadline of 30 April 2027. If it files seven months late while still owing £8,000 of Corporation Tax, the penalties stack up quickly, and come to far more than they would have under the old pre-2026 rules.
| Penalty component | Amount |
|---|---|
| Flat-rate: return filed late | £200 |
| Flat-rate: more than 3 months late | £200 |
| Tax-geared: 10% of £8,000 unpaid tax at 6 months | £800 |
| Total late filing penalties | £1,200 |
Under the old rules the flat-rate element would have been £100 plus £100, so £1,000 in total rather than £1,200. If the same company had also been late for the two previous years, the flat-rate element alone would jump to £1,000, pushing the bill to £1,800 before any interest on the unpaid tax. Planning ahead to file on time, and claiming every relief through our guide on how to reduce Corporation Tax legally, is far cheaper than any penalty.
Why has HMRC resumed automatic penalty notices?
HMRC paused automatic late filing penalty notices while it updated its systems for the higher 2026 rates, and confirmed in August 2026 that automatic notices had resumed. Companies that filed late during the pause can still expect a penalty notice, so do not assume a missed deadline has been overlooked by HMRC.
The resumption means penalty notices are once again being issued automatically as soon as a return passes its filing date. If you receive one, check the figures against the rates in this guide and against the official penalties page before you pay or appeal.
How do you appeal a corporation tax late filing penalty?
You can appeal a Corporation Tax late filing penalty within 30 days of the penalty notice if you have a reasonable excuse, such as a serious illness, a bereavement, or a genuine HMRC service failure. You must file the outstanding return first, and a shortage of funds or relying on an agent is rarely accepted as a reasonable excuse.
Appeals are made to HMRC in writing or online, following the process on gov.uk's appeal a tax penalty guidance. If you think the penalty is simply wrong, for example because the return was filed on time, you should contact HMRC with evidence rather than paying it. A broader view of Corporation Tax is in our complete guide to Corporation Tax.
Frequently asked questions
How much is the corporation tax late filing penalty in 2026?
From 1 April 2026, a Company Tax Return filed up to three months late carries a £200 penalty, rising to £400 if it is more than three months late. If Corporation Tax is also unpaid, HMRC adds tax-geared penalties of up to 20% of the tax owed once the return is six or more months overdue.
When did corporation tax late filing penalties increase?
The penalties doubled for returns with a filing date on or after 1 April 2026. It was the first increase since 1998, made because inflation had reduced the real value of the old fines to around half their original level.
What is the deadline for filing a Company Tax Return?
The CT600 must be filed within twelve months of the end of your accounting period. This is different from the Corporation Tax payment deadline, which is usually nine months and one day after the accounting period ends.
Can you appeal a corporation tax late filing penalty?
Yes. You can appeal within 30 days of the penalty notice if you have a reasonable excuse, such as serious illness, bereavement or an HMRC system failure. You must file the outstanding return first, and lack of funds is rarely accepted as an excuse.
Is the corporation tax filing deadline the same as the payment deadline?
No. The filing deadline is twelve months after your accounting period ends, while the payment deadline is usually nine months and one day after it ends. Filing late triggers these penalties; paying late triggers interest on the unpaid tax.
If you are worried about a looming Corporation Tax deadline or have already received a penalty notice, our team can get your CT600 filed correctly and deal with HMRC on your behalf. Explore our Corporation Tax services or book a free call to talk it through.
