If your company misses its Corporation Tax return deadline, HMRC will issue an automatic penalty. If it also misses the payment deadline, late payment interest starts accruing from the day after the due date. And if late filing happens repeatedly, the flat penalties escalate significantly.
This is not a compliance area that forgives you for being busy or disorganised. The deadlines are fixed, the penalties are automatic, and HMRC’s systems are increasingly effective at identifying late or missing company returns.
This guide covers the key deadlines, what the penalties look like, and the practical steps that keep your company on the right side of all of them.
Your Key Corporation Tax Deadlines at a Glance
One of the most common sources of confusion is that Corporation Tax involves separate deadlines, each with its own consequences if missed. They are not all the same date, and the payment deadline is earlier than many directors expect.
| Obligation | Deadline | Where Filed or Paid |
|---|---|---|
| Corporation Tax payment | Usually 9 months and 1 day after your Corporation Tax accounting period ends | HMRC |
| Annual accounts | Usually 9 months after your financial year-end for private companies | Companies House |
| Corporation Tax return (CT600) | 12 months after your Corporation Tax accounting period ends | HMRC |
To make this concrete: if your accounting period ends on 31 March 2026, your Corporation Tax is usually due to be paid by 1 January 2027, your Companies House accounts must usually be filed by 31 December 2026, and your CT600 return must be submitted by 31 March 2027.
The payment deadline comes before the filing deadline. This catches many directors out. You are required to calculate and pay what you owe before you have formally filed the return. This is why keeping your books and records current throughout the year matters so much. If you are scrambling to put numbers together at the last minute, you have very little chance of calculating the tax correctly and paying it on time.
Need Help With Your Accounts Or Tax?
Whether you need support with self assessment, VAT returns, payroll, bookkeeping, CIS, company accounts or corporation tax, Asmat & Co Accountants can provide clear, practical advice for your business or personal finances.
Large companies, broadly those with taxable profits above £1.5 million, may need to pay Corporation Tax by quarterly instalments. The threshold can be affected by associated companies, so if your company is approaching this level, taking advice in advance is important.
Our post on corporation tax covers the basics of how the tax is calculated and what qualifies as a deductible expense. Our post on limited company year-end accounts explains what is involved in preparing your statutory accounts, which underpin both your Companies House filing and your CT600.
What the Late CT600 Filing Penalties Look Like
HMRC’s late filing penalties for the Corporation Tax return are automatically triggered once you pass the 12-month filing deadline. These penalties increased from April 2026, so the flat penalties are now more expensive than many directors expect.
| How Late | Penalty |
|---|---|
| 1 day late | £200 |
| 3 months late | Another £200 |
| 6 months late | HMRC can estimate your Corporation Tax bill and add a penalty of 10% of the unpaid tax |
| 12 months late | A further 10% of any unpaid tax |
The percentage-based penalties only apply if there is unpaid Corporation Tax at the relevant point. However, because the payment deadline falls before the filing deadline, companies that are late filing often also have unpaid tax, especially where the accounts have not been prepared in time.
The combination of flat penalties, tax-geared penalties and late payment interest means that leaving a CT600 significantly overdue can become expensive quickly.
Our post on late tax returns and penalties gives a broader overview of HMRC’s penalty regime across different types of tax, which is useful context for understanding how Corporation Tax penalties fit into the wider compliance picture.
The Persistent Late Filer Problem
If your company files its CT600 late 3 times in a row, HMRC increases the flat penalties. Instead of the standard £200 penalties, the penalties can rise to £1,000 each.
That means a persistent late filer can face £2,000 in flat penalties for a single late CT600 before any tax-geared penalties or late payment interest are added.
This escalation is designed to prevent companies from treating the flat penalty as an acceptable cost of lateness. For any business where late filing is becoming a habit, the financial consequences increase quickly and the compliance record visible to third parties, such as buyers, lenders and suppliers, deteriorates.
If you have had late filings in recent years and are trying to get back on track before a funding application or a business sale, our post on amending a tax return is relevant for correcting past errors. And our post on HMRC enquiries and how an accountant can help covers what happens if repeated non-compliance leads to a formal enquiry.
Late Payment Interest: What It Costs You on Top of the Penalties
Separate from the filing penalties, HMRC charges interest on any Corporation Tax that is paid after the 9 months and 1 day deadline. This interest accrues from the day after the payment deadline until the date you actually pay.
From 6 April 2025, HMRC’s late payment interest rate for the main taxes is set at the Bank of England base rate plus 4 percentage points. As at January 2026, the published late payment interest rate is 7.75%.
On a £20,000 Corporation Tax bill paid 6 months late, late payment interest at 7.75% per year would be approximately £775. That stacks on top of any filing penalties and represents a genuine additional cost for something that is entirely avoidable.
HMRC does pay repayment interest when it owes you money, for example on a Corporation Tax overpayment. However, the repayment interest rate is lower than the late payment interest rate, so the interest position is not balanced equally between HMRC and the taxpayer.
Companies House Late Filing Penalties: A Separate Obligation
It is important to understand that filing your accounts at Companies House and filing your CT600 with HMRC are 2 separate obligations with 2 separate penalty regimes. Filing one does not automatically deal with the other.
Companies House has its own escalating penalty structure for private companies that file their annual accounts late.
| How Late (Private Company) | Penalty | Second Consecutive Year Late |
|---|---|---|
| Up to 1 month | £150 | £300 |
| 1 to 3 months | £375 | £750 |
| 3 to 6 months | £750 | £1,500 |
| More than 6 months | £1,500 | £3,000 |
The doubling of penalties for a second consecutive late filing is a significant deterrent. A private company that files more than 6 months late 2 years in a row faces a £3,000 Companies House penalty alone, before any HMRC Corporation Tax filing penalties are added.
Our post on understanding late filing fees at Companies House covers the Companies House penalty structure in full. Our post on Companies House identity verification covers the newer compliance requirements around director identity verification that also affect company records.
Why HMRC Is Increasing Compliance Enforcement
The regulatory environment for small companies has been tightening consistently in recent years. HMRC has invested in data analytics and digital systems that allow it to identify companies with late or missing returns more efficiently than in the past.
The introduction of Making Tax Digital for Income Tax also reflects a wider shift towards more frequent and accurate digital reporting. While Making Tax Digital for Corporation Tax is not proceeding as a separate programme, HMRC still expects company filings to be timely, complete and consistent.
Our post on how regtech is making compliance smarter covers how technology is changing the compliance landscape. Our post on the rise of AI and automation in accounting explains how both HMRC and accounting practices are using automation to improve accuracy and catch errors.
The practical result for small companies is that the tolerance for late filing is shrinking. Automatic penalties are applied without manual discretion, and HMRC’s ability to identify late filers has improved.
Our post on corporation tax mistakes that attract HMRC attention covers the specific errors that most frequently trigger deeper compliance activity beyond the standard late filing penalty.
Common Reasons Companies Miss Their Deadlines
Most late filings are not the result of deliberate non-compliance. They tend to come from predictable and avoidable situations.
The most frequent causes are:
- Bookkeeping being significantly out of date at the year-end, meaning accounts cannot be prepared until months of catch-up work is done
- The director not being aware of exactly when the deadline falls, particularly if the accounting period has been changed
- Using an accountant who is not proactive about chasing the necessary information well in advance of the deadline
- A change in accountant mid-year that results in a gap in oversight
- A difficult trading year that leads the director to deprioritise compliance while dealing with more immediate pressures
- Not having the cash to pay the Corporation Tax and therefore avoiding the issue, which does not stop penalties or interest
- Confusion between the Companies House accounts deadline and the HMRC CT600 deadline
- Assuming that no profit means no filing obligation
Our post on what to do if your bookkeeping is behind gives a practical recovery plan if your records have slipped to the point where preparing accounts feels impossible. And our post on cash flow forecasting for small businesses is relevant for making sure the Corporation Tax liability is built into your financial planning throughout the year so it does not come as a shock.
What to Do If You Are Already Late
If you have already missed a Corporation Tax deadline, the right response is to act as quickly as possible rather than waiting further. Every additional day of delay adds to the interest that will accrue, and waiting too long increases the risk of tax-geared penalties being triggered.
The steps to take are:
- Get your accounts prepared and the CT600 filed as soon as possible, even if you cannot pay the tax at the same time
- File before the return is 6 months late to reduce the risk of HMRC issuing a tax determination and a 10% tax-geared penalty
- Contact HMRC to discuss a Time to Pay arrangement if you cannot settle the full amount immediately
- Make sure your Companies House accounts are filed separately if they are also overdue
- Review any outstanding penalties with your accountant to confirm they are correct and whether grounds for appeal exist
- Check whether your accounting period dates are correct on HMRC’s systems if your year-end has changed
A penalty for late filing can only be appealed if you have a reasonable excuse. HMRC’s definition of reasonable excuse is narrow and does not typically include being busy, having cash flow problems, or waiting for your accountant to contact you. However, if there was a genuine and unforeseeable reason for the delay, such as serious illness, bereavement or a technical failure on HMRC’s systems, an appeal may be worth making with professional support.
Our post on tax return red flags that attract HMRC attention is useful background for understanding what else in your return might attract scrutiny once a late filing has been identified.
How Good Record-Keeping Prevents Late Filing
The most reliable way to avoid late filing penalties is to keep your financial records current throughout the year so that when the year-end arrives, the information needed to prepare your accounts and CT600 is already organised and accurate.
Monthly bookkeeping means that by the time your accounting year ends, your records need relatively little additional work to get to the point of preparing accounts. Our post on monthly bookkeeping with an online accountant explains how this works in practice and why it makes every compliance deadline far more manageable.
Regular financial reports throughout the year also give you a running estimate of your likely Corporation Tax liability. This means you can set aside the funds in advance and avoid the cash flow problem that often leads to companies avoiding their filing rather than confronting it.
Our post on how online accountants use management reports covers how good financial reporting supports better business decisions year-round, not just at compliance time.
How This Connects to Your Directors’ Personal Tax Obligations
Directors of limited companies may also have personal self-assessment obligations. Salary paid through the company, dividends received, benefits in kind and director’s loan account issues can all affect the director’s personal tax position.
The 31 January self-assessment deadline sits alongside the Corporation Tax filing calendar. For many director-shareholders, January and the months around the company year-end are particularly demanding periods.
Our post on self-assessment tax returns covers what needs to be reported on the director’s personal return. And our post on what is a director’s loan and how does it work is relevant if your director’s loan account needs to be reviewed for both company and personal tax purposes.
How Asmat & Co Accountants Can Help
As experienced limited company accountants based in Slough with nearly 2 decades of working with businesses across the region, Asmat & Co Accountants make sure your Corporation Tax deadlines are never missed. We take responsibility for preparing your annual accounts, calculating your Corporation Tax liability, submitting your CT600 to HMRC, and filing your accounts at Companies House, all well in advance of the relevant deadlines.
Our company accounts service covers the full preparation and filing process, and our tax return service handles both company and director tax compliance where needed.
We produce monthly or quarterly financial reports that keep you informed of your financial position and your estimated tax liability throughout the year, so there are no surprises at year-end and the funds are available when payment is due.
Our small business accountants team is available to businesses across Slough and the wider area, and our office serving accountants in Reading provides the same comprehensive service across Berkshire.
Our post on choosing the right accountant covers what to look for when evaluating whether your current accountant is being proactive enough about your compliance deadlines. And our post on switching to an online accountant explains how easy it is to move your accounting to a firm that takes a more proactive approach.
If you are currently managing without an accountant and considering whether the cost is justified, our post on pricing for online accountants and our post on the benefits of hiring an online accountant both give a realistic picture of what professional support costs and what it prevents.
Our post on what an accountant does for an SME gives a day-to-day picture of how a good accountant keeps your compliance on track throughout the year, not just at year-end.
Frequently Asked Questions
What happens if I cannot afford to pay my Corporation Tax on time?
File your CT600 on time regardless. Filing and payment are separate issues. Filing on time avoids the late filing penalty even if payment is late. If you cannot pay the full amount, contact HMRC as early as possible to discuss a Time to Pay arrangement. Late payment interest will still apply, but proactive engagement is far better than ignoring the debt.
Can I appeal a Corporation Tax late filing penalty?
Yes, if you have a genuine reasonable excuse. The appeal must usually be made within 30 days of the penalty notice and should explain clearly why the delay occurred. HMRC takes a narrow view of what counts as a reasonable excuse. Being busy, lacking funds or waiting for routine information from a third party does not typically qualify. Serious illness, bereavement or a genuine HMRC system failure may be accepted depending on the facts.
My accounting period changed last year. How does that affect my deadlines?
A change in accounting period can create a short or long accounting period. Corporation Tax accounting periods cannot be longer than 12 months, so a long set of accounts may require 2 CT600 returns and 2 payment deadlines. If your accounting period has changed recently, confirming your exact deadlines with your accountant is important.
Do I need to file a CT600 even if my company made no profit?
Yes, if HMRC has issued a notice to deliver a Company Tax Return for that accounting period. A company that is active normally needs to file a CT600 even if no Corporation Tax is due. Filing a nil return late can still attract flat late filing penalties.
My company is dormant. Do the same filing requirements apply?
A genuinely dormant company has simpler filing obligations, but it must still file dormant accounts and confirmation statements with Companies House. For HMRC, if the company is dormant for Corporation Tax and HMRC has been told, it may not need to file a CT600 unless HMRC issues a notice to deliver one. A company that describes itself as dormant but is still receiving income or making payments does not meet the usual dormant company position and may need full filings.
What if I have missed multiple years of Corporation Tax returns?
This needs to be addressed urgently and professionally. HMRC can issue estimated tax determinations where no return has been filed, and these may be higher than the actual liability. Filing the outstanding returns as quickly as possible, even if payment cannot be made immediately, gives you the best chance of replacing estimates with accurate figures and agreeing a manageable payment arrangement.
Does taking a dividend from my company affect my Corporation Tax liability?
No. Dividends are paid from post-tax profits and are not deductible against Corporation Tax. However, if you are paying yourself a combination of salary and dividends, the salary element is usually deductible and can reduce taxable profits, provided it is properly processed through payroll. Our post on director pay: salary vs dividends covers how to structure this efficiently.
Get Your Corporation Tax Under Control
Missed deadlines, accumulated penalties and late payment interest are avoidable costs. With the right accountant managing your compliance calendar and keeping your records current throughout the year, your Corporation Tax return and payment can be handled on time and your company’s compliance record can remain clean.
Contact Asmat and Co today and let us take your Corporation Tax and company accounts off your plate completely.
Need Help With Your Accounts Or Tax?
Whether you need support with self assessment, VAT returns, payroll, bookkeeping, CIS, company accounts or corporation tax, Asmat & Co Accountants can provide clear, practical advice for your business or personal finances.
