Introduction

Corporation Tax is not billed by HMRC. Your company works out its own tax, pays it, and reports it on a Company Tax Return. Because payment falls due before the return, many directors miss one of the two dates and only find out when a penalty notice arrives.

The cost of missing the return deadline has also risen recently. HMRC doubled its fixed late filing penalties for returns due on or after 1 April 2026, so an overdue CT600 is more expensive than it was a year ago.

This guide explains when Corporation Tax is due, when the CT600 must be filed, how penalties and interest work, and how to appeal. It also covers the 2026 changes that affect how returns are filed.

Quick Answer: What Are the UK Corporation Tax Deadlines and Penalties?

Most companies must pay Corporation Tax 9 months and 1 day after their accounting period ends, and file the Company Tax Return within 12 months of that date. For returns due on or after 1 April 2026, a late return costs £200 immediately, rising to £400 after three months, plus further charges if it stays outstanding. Interest is charged separately on unpaid tax.

Key points:

• Payment deadline: 9 months and 1 day after the accounting period ends.
• Filing deadline: 12 months after the accounting period ends.
• A return is required even if there is a loss or no tax to pay.
• Late payment attracts daily interest, not usually a fixed penalty.
• Companies House has its own, separate accounts deadline and penalties.

What Is UK Corporation Tax, and Which Rate Applies?

Corporation Tax is the tax a company pays on its taxable profits. Companies and associations that receive a notice to deliver a Company Tax Return must report their profits to HMRC. It is different from Income Tax, which individuals pay. ICT explains the distinction in its guide to corporate tax vs income tax.

Which Corporation Tax Rate Applies?

For companies with profits over £250,000, the main rate is 25%. Companies with profits between £50,000 and £250,000 pay the main rate reduced by marginal relief, which creates a gradual increase in the effective rate. A 19% small profits rate applies to companies with profits of £50,000 or less. The limits are reduced where a company has associated companies, so a group of companies should check its position carefully.

Rates are set for each financial year starting on 1 April, so confirm the current figures on GOV.UK before you calculate a bill. For planning ideas once you know your rate, see ICT’s guide to corporate tax planning.

What Is the Difference Between an Accounting Period and a Financial Year?

An accounting period is the period your return covers. It usually follows your company’s own accounts year. HMRC cannot accept a Corporation Tax accounting period longer than 12 months. The government’s “financial year” is the fixed 1 April to 31 March year that rates are set for. You pay tax at the rates that applied during your company’s accounting period.

The distinction matters because both of your deadlines run from the end of your accounting period, not from 31 March. If you are comparing systems, ICT’s overview of corporate tax in Pakistan shows how Pakistan frames its own tax year.

What Is a Corporation Tax Return, and Who Must File One?

A Company Tax Return is the report a company sends to HMRC after each accounting period. It shows the company’s taxable profit and the Corporation Tax due.

What Is a CT600?

The CT600 is the main form of the Company Tax Return. When you file, you calculate your profit or loss for Corporation Tax purposes, which can differ from the profit in your annual accounts, and your resulting tax bill. Related supplementary pages (such as CT600A and CT600L) are used in specific situations.

Does Every Company Have to File?

You must file if HMRC sends you a notice to deliver a Company Tax Return, and you must still file if the company made a loss or owes no tax. Sole traders and partnerships do not file this return. They use Self Assessment instead, which is covered in ICT’s guide to HMRC Self Assessment for Pakistani and UK taxpayers.

If you want the wider picture of personal and company filing in the UK, see ICT’s explainer on the UK tax return in 2026.

Do You Have to Register for Corporation Tax First?

Yes. A new company should tell HMRC it is active within three months of starting business activity. If HMRC has not sent you a notice to deliver a return, you must still tell it that the company has taxable profits. That notification is due within 12 months of the end of the accounting period, and failing to do so can lead to a “failure to notify” penalty.

When Is Corporation Tax Due, and When Must the CT600 Be Filed?

Two separate deadlines run from the same date: the end of your accounting period.

What Are the Two Deadlines?

For taxable profits up to £1.5 million, Corporation Tax must be paid 9 months and 1 day after the accounting period ends. The CT600 filing deadline is later: 12 months after the accounting period ends.

Paying on time does not excuse a late return. Filing on time does not excuse late payment.

How Do You Calculate Your Deadlines From Your Year End?

Count forward from the last day of your accounting period. These examples apply the standard rules:

1 January 2027 is a bank holiday. If a deadline falls on a weekend or bank holiday, your payment must reach HMRC on the last working day before it, unless you pay by Faster Payments through online or telephone banking.

Your own dates appear on HMRC’s notice to deliver a return and in your company’s HMRC online account. For ICT’s wider overview of dates, see the Pakistan tax calendar 2026, which is useful for directors who also handle FBR deadlines.

What If Your First Accounting Period Is Longer Than 12 Months?

HMRC cannot accept a Corporation Tax accounting period longer than 12 months, so a longer period of account is split into two. You may therefore file two returns for the same set of accounts. Check each period’s dates on your HMRC notices and do not assume they share one deadline.

Do Larger Companies Pay Differently?

Companies with taxable profits above £1.5 million pay in instalments rather than in one payment. Instalment rules and very large company rules have their own deadlines on GOV.UK. This guide focuses on the standard single-payment regime.

What Special Situations Change Your Corporation Tax Deadlines?

Standard dates assume a normal 12-month period. Some events change the dates, so recalculate whenever your accounting period changes.

What Happens If You Change Your Year End or Have a Short Accounting Period?

Both Corporation Tax deadlines run from the end of each accounting period. A shorter period therefore brings both dates forward. Changing the accounting period can also shorten the Companies House filing deadline, which often catches directors by surprise.

Before you change your year end, write down the new payment, return and accounts dates. A company secretary or adviser can handle the Companies House side. ICT’s company secretary course covers this kind of statutory work.

What If a Company Has More Than One Accounting Period in a Year?

This happens in a company’s first year or after a long period of account is split. Each accounting period has its own return and its own payment date. Keep a separate line in your calendar for each one, and use the correct payment reference for the period you are paying.

What Happens When a Company Stops Trading?

Stopping trading does not end your HMRC duties straight away. When you close a company through strike-off, GOV.UK tells you to file the accounts and Company Tax Return stating they are the final trading accounts, and to pay all Corporation Tax and other outstanding liabilities. Pay the tax before distributing money to shareholders, and take advice if the company has assets or loans.

How Do Corporation Tax Deadlines Differ From Companies House Deadlines?

A UK limited company reports to two bodies. HMRC receives the tax return and tax. Companies House receives the statutory accounts.

Private companies generally have 9 months to file annual accounts, and a newly incorporated company has 21 months from incorporation for its first accounts. Companies House penalties for private companies are £150 up to one month late, £375 for one to three months, £750 for three to six months, and £1,500 beyond six months. These penalties can double if accounts are late in two consecutive years. You can review the official statutory accounts submission penalty bands on GOV.UK.

The two systems run independently. A company can face a Companies House penalty and an HMRC penalty for the same year.

What Is the Difference Between a Corporation Tax Return and Annual Accounts?

The two documents are related but serve different purposes.

• Annual accounts are the company’s statutory financial statements, filed with Companies House and available on the public register.
• The Company Tax Return (CT600) goes to HMRC and calculates the tax due.

The profit used for Corporation Tax can differ from the profit shown in your annual accounts. The accounts are the starting point, and the tax computation adjusts them. Depending on the company, you may be able to file accounts and the tax return together. Modern filing software often lets you prepare both from the same data.

To understand how company law and tax law fit together, see ICT’s corporate law and taxation guide.

What Happens If You File Your Company Tax Return Late?

HMRC applies penalties automatically once the filing deadline passes. They apply even when the company owes no tax.

What Are the Fixed and Tax-Related Penalties?

The current HMRC late filing penalty structure is as follows.

If your return is late three times in a row, the £200 penalties rise to £1,000 each. A tax determination issued at six months cannot be appealed. You must pay the tax and file the return, after which HMRC recalculates interest and penalties.

When Did the New Amounts Start?

The higher rates apply to Company Tax Returns whose filing date is on or after 1 April 2026. The filing date decides which rate applies, not the accounting period end. A period that ended in 2025 can still fall under the new rules if its filing deadline lands on or after 1 April 2026.

For returns with an earlier filing date, the previous amounts were £100, £200, £500 and £1,000.

What Does a Late Return Cost in Practice?

These are simplified illustrations using the published rules, not predictions of an actual HMRC calculation.

• Return 5 months late, no tax unpaid: £200 + £200 = £400.
• Return 7 months late, £20,000 still unpaid: £400 in fixed penalties plus 10% of £20,000 (£2,000) = £2,400, before interest.

Filing even a few days after the deadline still triggers the first £200. This is why many accountants treat the filing date as fixed.

Example: What Happens If a Return Is Filed One Day Late?

This is a hypothetical illustration, not a real case.

A company’s accounting period ends on 31 December 2025. Its payment deadline is 1 October 2026 and its return deadline is 31 December 2026. The company pays its tax on time but files the CT600 on 1 January 2027.

• The return is one day late, so the first fixed penalty applies. The filing date is after 1 April 2026, so the higher £200 rate applies.
• No tax-related percentage penalty applies yet, because those start at six months.
• No interest arises, because the tax was paid by the payment deadline.

The company must have filed the return before it can appeal, and it needs the UTR, penalty notice date, amount and accounting period end date to do so. A single day’s delay therefore still costs money, which is why many advisers treat the filing date as fixed. ICT’s career-focused guide to UK taxation and HMRC work shows how professionals manage these dates for clients.

How Does HMRC Charge Interest on Late Corporation Tax Payments?

Interest is charged on unpaid Corporation Tax from the day after the payment deadline until it is paid. It is separate from filing penalties.

What Is the Current Rate?

The late payment rate was set at 7.75% from 9 January 2026, calculated as the Bank of England base rate plus 4%. You can check the latest Corporation Tax interest charges on GOV.UK, because the rate moves when the base rate changes.

How Do You Calculate It?

Use simple daily interest: tax unpaid × rate × days late ÷ 365.

Example: £20,000 unpaid for 90 days at 7.75% is £20,000 × 0.0775 × 90 ÷ 365, or about £382. The real figure will differ if the rate changes during the period.

Corporation Tax generally carries no fixed late payment penalty. The cost is mainly interest. Paying early or even an estimated amount on time reduces the interest bill.

What Is the Difference Between a Late Filing Penalty and Late Payment Interest?

Directors often confuse the two charges.

Corporation Tax does not normally carry a fixed penalty for paying late. The cost of paying late is mainly interest, at the rate set by HMRC. You can be charged both a filing penalty and interest in the same year.

FBR’s late filing rules in Pakistan work differently. For that, see ICT’s explainer on the FBR late filer surcharge.

What Other Corporation Tax Penalties Can Apply?

Late filing is not the only risk.

• Failure to notify. If you do not tell HMRC the company is liable, the penalty is based on the tax involved. The maximum is 30% for non-deliberate failures, 70% for deliberate but not concealed, and 100% for deliberate and concealed.
• Inaccurate returns. The penalty is a percentage of the extra tax due. It is lower if you disclose the error to HMRC before it finds out.
• Poor records. Companies must keep sufficient records to support a complete and accurate return.
• Instalment errors. Deliberately missing or understating instalments can attract penalties.

Good record-keeping and prompt correction are your best protection. This is also why corporate tax planning and compliance work well together. ICT covers the planning side in its guide to corporate tax planning.

What Happens If HMRC Opens a Compliance Check on Your Company Tax Return?

HMRC may check a return for errors. GOV.UK notes that HMRC may check for errors in a Company Tax Return and may charge a penalty for them.

How Long Does HMRC Have to Open an Enquiry?

HMRC must normally give notice of an enquiry within 12 months of the date the return was filed, and there is no maximum duration set for an enquiry. Different time limits can apply if a return is filed late or amended, so take advice if you receive an enquiry letter.

How Can You Reduce the Risk?

• Keep records that support every figure on the return.
• Correct errors as soon as you notice them. Penalty percentages for inaccuracies are lower where you disclose an error before HMRC finds it.
• Answer HMRC’s questions fully and on time.

You may also need to keep records for longer than the usual period if HMRC has started a compliance check. ICT’s UK Taxation Course includes HMRC investigations and penalty mitigation in its outline. You can review the details on the UK Taxation Course page.

What Are the Latest Rules and Changes in 2026?

Three developments matter for directors filing now.

Penalties doubled. As explained above, fixed late filing penalties doubled for returns due from 1 April 2026.

HMRC’s free filing tool closed. The joint online service for filing company accounts and Company Tax Returns closed on 31 March 2026. From 1 April 2026, you need commercial software to file annual accounts and Company Tax Returns with HMRC. A paper return is only allowed in limited cases, such as a reasonable excuse or filing in Welsh. Choosing software early avoids a last-minute scramble. ICT’s guides to software tax professionals use and cloud accounting with Xero explain the common options.

Companies House reforms were paused. Proposals to require software-only accounts filing from 1 April 2027 were reported as paused and under review in January 2026, with a promise of at least 21 months’ notice before any change. Check Companies House guidance before relying on older articles that still describe a 2027 switch.

Do Dormant Companies and Overseas Directors Have Different Rules?

What About Dormant Companies?

Once you tell HMRC your company is dormant for Corporation Tax, you do not have to file another Company Tax Return unless HMRC asks you to or you begin trading again. You still have to send information about a dormant company to Companies House. Until HMRC records dormancy, an issued notice still has to be answered, even with a nil return.

What About Directors Living Abroad?

Deadlines follow the company’s accounting period. HMRC’s published rules do not give extra time because a director lives overseas. This is our reading of those rules, so confirm anything unusual with a qualified adviser.

Practical points for overseas directors, including those in Pakistan:

• Make sure the registered office can forward HMRC post quickly, or use the company’s HMRC online account.
• Keep a shared calendar of both deadlines, with reminders at least a month ahead.
• Allow for payment clearing time when sending funds from outside the UK.

For related guidance, see ICT’s articles on cross-border tax compliance, overseas Pakistanis’ tax filing and double taxation relief.

What Documents Do You Need Before Filing a CT600?

Gather these before you open your filing software:

• Your company’s Unique Taxpayer Reference (UTR) and 17-character payment reference.
• Finalised statutory accounts for the accounting period.
• A Corporation Tax computation adjusting accounting profit to taxable profit.
• Bank statements, sales invoices and purchase receipts.
• Payroll and director-related records, including dividend paperwork.
• Capital allowance and fixed asset records.
• Details of loans, associated companies and any reliefs you plan to claim.

Cloud tools make this easier. ICT has guides on QuickBooks, Odoo accounting and AI for bookkeeping.

How Long Must You Keep Corporation Tax Records?

A limited company must keep records for 6 years from the end of the last company financial year they relate to. You must keep them longer if a transaction covers more than one accounting period, if the company bought long-life equipment, if you sent your return late, or if HMRC has begun a compliance check.

How Can You File a CT600 Step by Step?

1. Confirm the accounting period and both deadlines from your HMRC notice or online account.
2. Finalise the statutory accounts, which feed the Corporation Tax computation.
3. Prepare the tax computation, adjusting accounting profit to taxable profit.
4. Choose HMRC-recognised commercial software or an agent.
5. Complete and submit the CT600 with the required accounts and computations.
6. Pay the tax using the correct reference. The 17-character Corporation Tax payment reference appears on your notice, HMRC reminders and your HMRC online account. A wrong reference can delay payment or credit another bill.
7. Check HMRC received the payment and keep your confirmation.

To understand how corporate law and tax filing connect, read ICT’s guide on how corporate law and taxation work together.

How Do You Correct or Amend a Corporation Tax Return After Filing?

Mistakes can be corrected, but there is a time limit.

What Is the Deadline to Amend a CT600?

You must usually make changes within 12 months of the filing deadline, using commercial software or by writing to or sending a paper return to the Corporation Tax office. The window runs from the filing deadline, not from the day you submitted.

For example, with a 31 March 2026 year end the filing deadline is 31 March 2027, so amendments would normally be due by 31 March 2028.

What If the Return Was Filed Late?

The amendment time limit is not extended when a return is delivered late. If a return is delivered more than 12 months late, no amendment can be accepted. That is another reason to file on time.

What If the 12 Months Have Passed?

Write to HMRC explaining the error, and take advice about interest and penalties. Telling HMRC promptly generally reduces penalties. For comparison with other UK filings, see ICT’s guide to UK tax return filing.

What Are the Most Common Mistakes With Corporation Tax Deadlines?

1. Mixing up the two deadlines. Payment falls at 9 months and 1 day. Filing falls at 12 months.
2. Assuming no return is needed. A return is still required with a loss or no tax due.
3. Waiting for a bill. HMRC does not send one. You calculate, report and pay yourself.
4. Using old penalty amounts. The £100 figure applies only to earlier filing dates.
5. Using the wrong payment reference. A wrong reference can delay payment or credit another tax bill.
6. Missing bank holidays. Pay on the last working day before the deadline unless using Faster Payments.
7. Forgetting Companies House. Accounts have their own deadline and penalties.
8. Not telling HMRC about dormancy. HMRC keeps asking for returns until it is told.
9. Relying on closed tools. The free HMRC filing service has closed, so you now need commercial software.
10. Assuming an agent will cover everything. Confirm in writing who tracks deadlines.

ICT also lists common tax mistakes businesses make in its Pakistan-focused guide. Many of the compliance habits carry across jurisdictions.

How Can You Avoid Corporation Tax Penalties?

• Diary the payment date before the filing date, because it comes first.
• Treat the Companies House accounts deadline as a third date.
• Keep records organised through the year, not only at year end.
• Start the return well before the deadline so accounts are ready.
• Tell HMRC promptly if your company becomes active or dormant.
• Correct mistakes as soon as you find them.
• Use reminders or automation. ICT’s overview of AI tools for accountants covers helpful options.

What Does a Corporation Tax Compliance Checklist Look Like?

Use this timeline, counted from your accounting period end date.

Add each date to a shared calendar with reminders a month ahead. ICT’s Pakistan tax calendar and tax deadlines calendar for consultants show how professionals structure a year of deadlines.

What If You Cannot Pay on Time?

Contact HMRC before the deadline, not after. GOV.UK has guidance for businesses that cannot pay a tax bill on time. Interest still runs while a debt is outstanding, so even partial payment on time reduces the cost.

Can You Appeal a Late Filing Penalty?

Yes, if you have a reasonable excuse. You must file the Company Tax Return before appealing. The online form needs your company’s UTR, the date and amount on the penalty notice and the accounting period end date. You must complete it in one session, then print it and post it to the address on the form.

Describe what happened, when it started and what you did to put it right. A shortage of funds or reliance on someone else is rarely accepted on its own, so ask a qualified adviser if your case is borderline.

What Counts as a Reasonable Excuse?

HMRC looks at what a reasonable person who wanted to comply would have done in the same situation. Examples that HMRC commonly treats as reasonable include serious illness, the death of a close partner shortly before the deadline, unexpected postal delays, or losing important documents to theft, fire or flood.

Excuses that are usually weak include forgetting the date, making a mistake, not receiving a reminder, or relying on someone else. Not receiving a reminder, relying on someone else and making a mistake are among the reasons not counted. Cash flow problems are also unlikely to qualify as an excuse for late payment.

Even where an excuse is valid, you should put things right as soon as you are able. Appeals in Pakistan follow a different route, covered in ICT’s guide to tax appeals in Pakistan.

Should You Use an Accountant or File Yourself?

You can do either. An accountant can prepare and file the return, or you can do it yourself. Fees vary widely by company size and complexity, so request a written quote and confirm who handles deadlines and penalty notices.

If you want to build the skills yourself, start with ICT’s UK taxation exam guide and the Xero accounting course.

What Skills and Careers Are Linked to UK Corporation Tax Compliance?

Managing deadlines, penalties and returns is a core skill for anyone supporting UK companies. Useful skills include:

• Preparing Corporation Tax computations and CT600 returns.
• Tracking payment, filing and Companies House dates.
• Using cloud accounting and filing software.
• Handling HMRC correspondence and penalty appeals.
• Explaining deadlines clearly to directors.

According to ICT’s course page, the UK Taxation Course is aimed at accountants, finance professionals, tax consultants and business owners. It describes pathways such as working with UK accounting firms, serving overseas Pakistani clients and joining global finance outsourcing companies.

To explore the paths, read ICT’s guides on becoming a UK tax consultant, UK taxation career paths and the career roadmap after a UK taxation course. For remote options, see remote tax jobs in 2026.

Why Choose ICT for UK Taxation Training in Pakistan

If you work with UK companies from Pakistan, or want to, deadlines and penalties are everyday work. According to ICT’s course page, its UK Taxation Course covers UK corporation tax computation, CT600 preparation and filing, HMRC compliance, penalty mitigation, and tax obligations for overseas Pakistanis. It lists delivery in Islamabad and Karachi and online across Pakistan.

ICT lists Mr. Muhammad Waqas as a mentor, described on the course page as a UK accounting specialist with 5+ years in FRS 102/105, corporation tax, VAT and compliance management. Certificates can be checked through ICT’s certificate verification page. Professionals who study alongside work may also find ICT’s article on studying tax while working full time useful.

Frequently Asked Questions

When is a UK Corporation Tax return due?
Twelve months after the end of the accounting period it covers.

When must Corporation Tax be paid?
For most companies, 9 months and 1 day after the accounting period ends.

How much is the late filing penalty?
For returns due on or after 1 April 2026, £200 at one day late and another £200 after three months. Further percentage penalties apply at six and twelve months.

Do I need to file if my company made a loss or has no tax to pay?
Yes, if HMRC has issued a notice to deliver a return.

What is the difference between the CT600 and annual accounts?
The CT600 goes to HMRC and calculates tax. Annual accounts go to Companies House and report the company’s finances.

Can I appeal a late filing penalty?
Yes, if you have a reasonable excuse, but you must file the return first.

Does a dormant company need to file a CT600?
Not after HMRC has been told it is dormant, unless HMRC asks for a return or trading restarts. Companies House filings still apply.

Can penalties increase over time?
Yes. Fixed penalties are added at three months, percentage penalties at six and twelve months, and fixed amounts rise to £1,000 each after repeated late returns.

If you want to build the skills yourself, start with ICT’s UK taxation exam guide and the Xero accounting course.

How do I check my deadline?
Use your HMRC notice or company online account for HMRC dates, and the Companies House register for the accounts deadline.

What is the UK Corporation Tax rate?
For companies with profits over £250,000 the main rate is 25%. Profits of £50,000 or less are taxed at 19%, with marginal relief in between. Check GOV.UK for current figures.

Can I file my Corporation Tax return after the deadline?
Yes, but penalties start the day after the deadline. File as soon as possible to limit them.

Can I amend a Corporation Tax return after submission?
Usually yes, within 12 months of the filing deadline, using commercial software or by writing to HMRC.

Does HMRC charge a penalty for paying Corporation Tax late?
Not normally a fixed penalty. HMRC charges daily interest on unpaid tax instead.

How long should a company keep tax records?
For 6 years from the end of the last company financial year they relate to, and longer in some situations.

What happens if a company stops trading?
It must usually file final accounts and a final Company Tax Return, and pay any Corporation Tax due before strike-off.

Do deadlines change if I change my year end?
Yes. Both deadlines run from the end of each accounting period, so a shorter period brings them forward.

Conclusion

Corporation Tax has two HMRC dates, plus a Companies House date, all counted from your accounting period end. Pay by 9 months and 1 day, file the CT600 within 12 months, and send your accounts to Companies House on time. Late filing now costs at least £200 for returns due from 1 April 2026, and unpaid tax attracts interest.

Build the dates into your calendar from day one, keep clean records, and file through commercial software. If you want to handle UK company tax professionally, explore ICT’s UK Taxation Course, apply online, or reach the team through the contact page or admissions@ict.edu.pk.