Corporation Tax Deadlines: A Practical Guide for UK Companies

Corporation Tax deadlines are among the most important dates on a UK company’s compliance calendar. Missing one can lead to penalties, interest and unnecessary administrative work, even if the company has made little or no profit. The key point is that the deadline for paying Corporation Tax is different from the deadline for filing the Company Tax Return.

For most UK companies, Corporation Tax is due 9 months and 1 day after the end of the accounting period, while the Company Tax Return is normally due 12 months after the end of that accounting period. That distinction matters. A company can have several months between paying its tax and filing its tax return, but waiting until the filing deadline to deal with the tax bill could mean paying too late.

This guide explains the main Corporation Tax deadlines, how they work for new companies and growing businesses, what happens when you miss them, and how founders can build a reliable tax calendar.

What Is Corporation Tax?

Corporation Tax is a tax charged on the taxable profits of companies and certain other organisations. For the 2026 financial year, the small profits rate is 19% for profits of £50,000 or less, while the main Corporation Tax rate is 25% for profits above £250,000. Companies with profits between these thresholds may qualify for Marginal Relief, which gradually increases the effective rate between the two limits.

Importantly, Corporation Tax is calculated on taxable profits, not simply the amount of money that enters the company's bank account. A company may have £150,000 in sales but considerably less taxable profit after allowable business expenses and relevant tax adjustments. Corporation Tax can apply to profits from activities such as:

• Trading income
• Certain investment income
• Chargeable gains
• Other taxable business profits

The exact calculation depends on the company's circumstances, accounting period, expenses, reliefs and other factors.

What Are the Main Corporation Tax Deadlines?

For most companies, there are three dates worth putting on the calendar:

The first two deadlines relate to HM Revenue & Customs (HMRC). The third relates to Companies House. They are separate obligations, even though the accounts and tax return use much of the same financial information.

Example: A 31 March Year-End

Suppose a company's Corporation Tax accounting period ends on 31 March 2026.

• 1 January 2027: Its typical Corporation Tax payment deadline.
• 31 March 2027: Its Company Tax Return deadline normally due.
• 31 December 2026: Meanwhile, its annual accounts would normally need to reach Companies House.

This is why business owners should avoid treating "the tax deadline" as a single date.

When Do You Pay Corporation Tax?

For companies with taxable profits of up to £1.5 million, Corporation Tax is generally payable 9 months and 1 day after the end of the accounting period. For example:

• Accounting period ends: 30 June 2026
• Corporation Tax payment deadline: 1 April 2027

The payment deadline is deliberately earlier than the Company Tax Return deadline. This creates an important cash-flow consideration for founders. You may need to estimate your Corporation Tax liability before your final tax return has been prepared.

Don't Confuse the Accounting Period with the Tax Year

Corporation Tax does not simply operate according to the calendar year. A company's accounting period might run from:

• 1 January to 31 December
• 1 April to 31 March
• 1 October to 30 September

The deadline is calculated from the company's relevant accounting period, which is why the company's own financial year-end should be checked rather than relying on a generic tax calendar.

When Is the Company Tax Return Due?

A Company Tax Return is normally due 12 months after the end of the accounting period it covers. The return is used to calculate the company's taxable profit and Corporation Tax liability. This is different from the company's annual accounts. A useful way to remember the distinction is:

• Accounts show the company's financial position.
• The Company Tax Return reports the company's tax position to HMRC.

The two are connected, but they are not interchangeable. A company generally has to file its Company Tax Return even when:

• It made a loss
• It has no Corporation Tax to pay
• It has very little activity
• It has eligible deductions or reliefs that reduce its liability to zero

HMRC specifically states that a company must still send a return if it makes a loss or has no Corporation Tax to pay.

Corporation Tax Deadlines for New Companies

New companies often find Corporation Tax deadlines confusing because the first year can involve different accounting periods. A newly incorporated company can have two Corporation Tax accounting periods within its first financial year.

This can happen because a Corporation Tax accounting period cannot normally exceed 12 months, even where the company's first set of accounts covers a longer period. For example, a company might be incorporated on 15 January 2026 and prepare its first accounts to 31 January 2027.

Its first accounts cover more than 12 months, but its Corporation Tax reporting may be split into separate accounting periods. This is one reason new founders should not assume that their Companies House accounts deadline automatically tells them when their Corporation Tax is payable.

What About Large Companies?

The standard "9 months and 1 day" rule is mainly relevant to companies with taxable profits of up to £1.5 million. Companies with taxable profits above £1.5 million will generally have to pay Corporation Tax by instalments rather than making one payment after the year-end. Different rules apply to companies with profits above £20 million.

For a fast-growing business, this can materially change cash-flow planning. A company that moves from a small or medium-sized business into large-company territory should review its payment schedule before the end of the accounting period rather than waiting for HMRC to issue a reminder. There are exceptions and special rules, particularly for companies entering the Corporation Tax regime for the first time, so large businesses should calculate their position carefully.

What Happens If You Miss the Corporation Tax Payment Deadline?

Late payment can result in interest and penalties. The financial consequences can be particularly frustrating because the tax liability itself does not disappear simply because the company cannot pay on time. If a company knows it will struggle to pay, it is generally better to address the problem promptly than to ignore HMRC correspondence. The company should establish:

• How much Corporation Tax is due
• How much has already been paid
• Why the payment cannot be made on time
• Whether a payment arrangement may be available
• What interest or penalties may apply

Cash-flow problems are not the same as tax problems, but they can quickly become both if a company does not plan ahead.

What Happens If You File the Company Tax Return Late?

HMRC can charge penalties even where there is no Corporation Tax to pay. Current late-filing penalties include:

• 1 day late: £200
• 3 months late: An additional £200
• 6 months late: HMRC may estimate the Corporation Tax and add a penalty of 10% of unpaid tax
• 12 months late: Another 10% of unpaid tax may apply

If a Company Tax Return is late three times in succession, the £200 penalties can increase to £1,000 each.

Key Rule: No tax due does not mean no filing obligation. A dormant or loss-making company can still have compliance responsibilities.

Can You Appeal a Corporation Tax Penalty?

Yes, in appropriate circumstances. HMRC allows companies to appeal certain late-filing penalties where they have a reasonable excuse for missing the deadline. The company must explain why it could not file on time and provide relevant evidence. A director should not assume that simply forgetting the deadline will automatically qualify as a reasonable excuse.

If a penalty is received, deal with it promptly, establish why it arose and determine whether an appeal is appropriate. Most importantly, file the outstanding return. Appealing a penalty does not remove the underlying filing obligation.

Corporation Tax vs Companies House: Which Deadline Comes First?

This is one of the most common sources of confusion for company directors. For a typical private limited company:

• Companies House accounts: Usually due 9 months after the financial year-end.
• Corporation Tax payment: Usually due 9 months and 1 day after the Corporation Tax accounting period ends.
• Company Tax Return: Usually due 12 months after the Corporation Tax accounting period ends.

The dates can therefore look very similar while referring to completely different obligations. A practical compliance calendar should track Companies House and HMRC separately, even when the same accountant handles both.

How Founders Can Avoid Corporation Tax Deadline Problems

The easiest way to manage Corporation Tax deadlines is to stop treating them as annual surprises.

1. Record the company's accounting period

Know exactly when the relevant accounting period ends. Do not rely solely on memory or the date your company was incorporated.

2. Put three deadlines in your calendar

Record:

• Companies House accounts deadline
• Corporation Tax payment deadline
• Company Tax Return deadline

Set reminders well before the actual dates.

3. Estimate tax before the deadline

Don't wait until the final return is ready to discover that the business owes £20,000. A rolling estimate of taxable profit can help directors reserve money throughout the year.

4. Keep business records organised

Maintain accurate records of:

• Sales
• Business expenses
• Payroll
• Bank transactions
• Assets
• Loans
• Dividends
• Director transactions
• Relevant invoices and receipts

Good bookkeeping makes the eventual Corporation Tax calculation much easier.

5. Consider tax reliefs and allowances

The amount of Corporation Tax due can be affected by legitimate deductions and reliefs. Depending on the business, these may include capital allowances, trading losses, R&D-related reliefs and other available tax provisions. Don't confuse legitimate tax planning with simply reducing the figures. Claims need to be supported by the relevant rules and records.

6. Review deadlines when the business changes

A change in circumstances can affect tax planning. Review your arrangements if the company:

• Becomes profitable for the first time
• Acquires another company
• Becomes part of a group
• Changes its accounting year-end
• Starts trading internationally
• Makes significant asset purchases
• Begins claiming R&D or other specialist reliefs
• Experiences rapid growth

For global founders managing a UK company remotely, this is particularly important. The fact that the director lives outside the UK does not eliminate the company's UK filing and tax responsibilities.

A Simple Corporation Tax Deadline Checklist

Before each accounting period ends, ask:

Financial records

• [ ] Are the bookkeeping records complete?
• [ ] Are bank transactions reconciled?
• [ ] Are business expenses properly documented?

Tax

• [ ] Has taxable profit been estimated?
• [ ] Is enough cash reserved for Corporation Tax?
• [ ] Are relevant reliefs and allowances being considered?

Companies House

• [ ] Is the annual accounts deadline recorded?
• [ ] Are company details and director information up to date?

HMRC

• [ ] Is the Corporation Tax payment deadline recorded?
• [ ] Is the Company Tax Return deadline recorded?
• [ ] Are HMRC messages and notices being monitored?

Cash flow

• [ ] Can the company afford the expected tax payment?
• [ ] If not, has the issue been addressed early?

This simple routine can prevent a surprisingly expensive administrative mistake.

FAQ: Corporation Tax Deadlines

When is Corporation Tax due in the UK?

For most companies with taxable profits of up to £1.5 million, Corporation Tax is normally due 9 months and 1 day after the end of the accounting period. Larger companies may have to pay by instalments.

When is a Company Tax Return due?

The usual deadline is 12 months after the end of the accounting period covered by the return.

Is the Corporation Tax payment deadline the same as the filing deadline?

No. Corporation Tax is generally payable earlier than the Company Tax Return is due.

Do I need to file a tax return if my company made no profit?

Yes. A company may still need to file a Company Tax Return even if it made a loss or has no Corporation Tax to pay.

What is the Corporation Tax rate in 2026?

For the 2026 financial year, the small profits rate is 19% for qualifying profits of £50,000 or less, while the main rate is 25% for profits above £250,000. Marginal Relief may apply between the thresholds.

Can a company pay Corporation Tax late?

A company can make a late payment, but interest and potentially penalties may apply. If cash flow is a problem, it is better to address the situation promptly rather than ignore the liability.

What happens if I miss my Company Tax Return deadline?

HMRC can impose late-filing penalties, starting at £200 for one day late. Further penalties can apply as the delay increases.

Does a dormant company have Corporation Tax deadlines?

A dormant company can have different reporting requirements depending on its circumstances. Being dormant does not automatically mean every HMRC or Companies House obligation disappears.

Final Thoughts

Corporation Tax deadlines are easier to manage when you separate three different responsibilities: filing annual accounts with Companies House, paying Corporation Tax to HMRC, and filing the Company Tax Return. For most companies, the critical dates are straightforward: Corporation Tax is normally due 9 months and 1 day after the accounting period ends, while the Company Tax Return is generally due 12 months after it ends.

The real challenge is not knowing the dates, it is preparing for them. Founders should monitor profit throughout the year, keep records current, reserve cash for tax and maintain a calendar covering both Companies House and HMRC obligations. For international founders using a UK company, these disciplines become even more important because geographical distance does not remove UK compliance responsibilities.

IncorpUK, as a UK company formation and management platform for global founders, sits within this wider compliance landscape: forming a company is only the beginning. Keeping its tax, accounting and statutory obligations organised is what helps turn a registered company into a properly maintained business.