Corporation Tax Deadlines Every UK Business Must Know

When Is Corporation Tax Due?

For companies with taxable profits of £1.5 million or less, Corporation Tax is generally due 9 months and 1 day after the end of the accounting period.

For example, if your company’s Corporation Tax accounting period ends on 31 March 2026, the Corporation Tax payment deadline would normally be 1 January 2027.

This deadline is earlier than the Company Tax Return filing deadline, giving businesses time to submit their tax return after making the payment.

Example

If your accounting period ends on 31 March:

The exact deadline depends on your company’s accounting period, so businesses should not assume that every company has the same Corporation Tax payment date.

When Is the Company Tax Return Due?

Your Company Tax Return is generally due 12 months after the end of the accounting period covered by the return.

For example, if your accounting period ends on 31 March 2026, your Company Tax Return would normally need to be filed by 31 March 2027.

Importantly, the filing deadline is separate from the Corporation Tax payment deadline.

This means a company cannot assume that it has until the tax return deadline to pay its Corporation Tax.

Remember the 9-month-and-1-day rule

A useful way to remember the standard deadlines is:

Pay Corporation Tax: 9 months and 1 day after the accounting period ends.

File Company Tax Return: 12 months after the accounting period ends.

Corporation Tax Payment Deadline vs Filing Deadline

One of the most common Corporation Tax mistakes is confusing the payment deadline with the filing deadline.

They are two separate obligations.

For a typical company:

Accounting period ends → Corporation Tax payment due → Company Tax Return due

For example:

31 March 2026 → 1 January 2027 → 31 March 2027

HMRC confirms that the Corporation Tax payment deadline comes before the Company Tax Return filing deadline.

Therefore, businesses should calculate their expected tax liability well before the payment deadline rather than waiting until the return is ready to be filed.

What About Companies With Profits Above £1.5 Million?

The standard 9-month-and-1-day payment rule does not apply in the same way to companies with higher taxable profits.

Companies with taxable profits between £1.5 million and £20 million will generally need to pay Corporation Tax through quarterly instalments, subject to specific rules and exceptions.

For a 12-month accounting period, instalment dates generally fall:

• 6 months and 13 days after the start of the accounting period
• 3 months after the first instalment
• 3 months after the second instalment
• 3 months and 14 days after the end of the accounting period

The rules can become more complicated where a company has associated companies, a shorter accounting period or other special circumstances.

Corporation Tax Deadlines for Very Large Companies

Companies with taxable profits of more than £20 million are generally subject to the quarterly instalment regime for very large companies.

For a 12-month accounting period, payments are generally due on the 14th day of months 3, 6, 9 and 12 of the accounting period.

Because these businesses make tax payments much earlier than companies using the standard payment system, accurate tax forecasting and cash-flow planning are particularly important.

What Is the Deadline for a Newly Formed Company?

New companies can have different accounting and filing arrangements during their first year.

A company may have a Corporation Tax accounting period that does not exactly match its Companies House financial year. In some circumstances, a company can also have more than one Corporation Tax accounting period during its first financial year.

This is why newly incorporated businesses should establish their Corporation Tax accounting period and deadlines as early as possible.

Your first set of accounts and Corporation Tax obligations can involve different deadlines, so professional advice can help prevent missed filings.

What Happens If You Miss the Corporation Tax Payment Deadline?

Failing to pay Corporation Tax on time can result in interest being charged on late payments. HMRC also applies penalties in circumstances where relevant filing obligations are missed.

Late payment can also create unnecessary cash-flow pressure and make it harder for your business to manage its finances effectively.

If you think your company may struggle to pay its Corporation Tax bill, it is better to review your position and seek professional advice as early as possible rather than simply allowing the deadline to pass.

What Happens If You File Your Company Tax Return Late?

A Company Tax Return must generally be filed within 12 months of the end of the accounting period.

HMRC can charge late filing penalties even if your company has no Corporation Tax to pay.

This is an important point for businesses that have made a loss or have little or no Corporation Tax liability.

You should therefore treat the filing deadline as a separate compliance requirement rather than assuming that no tax liability means no return is required.

Corporation Tax and Companies House Deadlines Are Different

Another common source of confusion is the difference between HMRC Corporation Tax deadlines and Companies House filing deadlines.

A private limited company generally has to:

• Prepare annual accounts
• File annual accounts with Companies House
• Pay Corporation Tax to HMRC
• File its Company Tax Return with HMRC

For most private companies, annual accounts are generally due at Companies House 9 months after the end of the financial year, while Corporation Tax is usually due 9 months and 1 day after the end of the Corporation Tax accounting period. The Company Tax Return is generally due 12 months after the accounting period ends.

These deadlines may be close together but they are not the same.

How Can UK Businesses Stay on Top of Corporation Tax Deadlines?

Good tax compliance starts well before the deadline.

1. Know Your Accounting Period

Make sure you know exactly when your Corporation Tax accounting period begins and ends. Your key tax deadlines are calculated from this period.

2. Maintain Accurate Bookkeeping

Up-to-date bookkeeping gives you a clearer picture of your company’s income, expenses and profitability. It also makes Corporation Tax calculations and year-end accounts preparation more efficient.

3. Forecast Your Corporation Tax Liability

Don’t wait until the deadline to find out how much tax your company may owe. Regular tax forecasting can help you plan for the payment and avoid unexpected cash-flow problems.

4. Keep Business Records Organised

Maintain appropriate records of sales, purchases, expenses, payroll, assets, bank transactions and other relevant financial information.

5. Start Preparing Early

Preparing your accounts and Corporation Tax information several months before the deadline gives you time to identify errors, gather missing documents and address potential tax issues.

6. Use Professional Accounting Support

An accountant can help you monitor deadlines, prepare accounts, calculate Corporation Tax and submit your Company Tax Return correctly.

Corporation Tax Deadline Checklist for UK Businesses

Use this simple checklist to help manage your Corporation Tax obligations:

• Confirm your Corporation Tax accounting period.
• Record your Corporation Tax payment deadline.
• Estimate your Corporation Tax liability.
• Keep bookkeeping records up to date.
• Review allowable business expenses and tax adjustments.
• Prepare your annual accounts.
• Prepare your Company Tax Return.
• Pay Corporation Tax by the applicable deadline.
• File your Company Tax Return by the deadline.
• Keep evidence of payments and submitted returns.

Review future tax liabilities and cash flow.