Key Corporation Tax Dates UK Business Owners Should Know

Keeping track of Corporation Tax deadlines is essential for every UK limited company. Missing a filing or payment date can result in automatic penalties, interest charges, and HMRC scrutiny.

Corporation Tax has different deadlines for filing and payment, and these depend on your company’s accounting period, not the personal tax year.

This guide explains the key Corporation Tax dates UK business owners need to know, including CT600 deadlines, payment dates, Companies House filing requirements, and common pitfalls.

What Is Corporation Tax?

Corporation Tax is paid by UK limited companies on their taxable profits, including:

• Trading profits
• Investment income
• Chargeable gains

Every limited company must:

• Register for Corporation Tax
• File a CT600 Corporation Tax return
• Pay Corporation Tax by the required deadline

Understanding Your Company Accounting Period

Unlike individuals, companies do not follow the standard UK tax year.

Your accounting period:

• Usually runs for 12 months
• Can be changed
• Determines when your tax return and payment are due

Many companies choose 31 March to align with the UK tax year, but this is not required.

Corporation Tax Payment Deadline

The Corporation Tax payment deadline is:

9 months and 1 day after the end of your accounting period

Example:

• Accounting period ends: 31 March 2025
• Corporation Tax due: 1 January 2026

This deadline is earlier than the filing deadline.

Large companies may need to pay Corporation Tax in quarterly instalments instead.

CT600 Filing Deadline

Your CT600 Corporation Tax return must be submitted:

12 months after the end of your accounting period

The CT600 must be filed:

• Online
• With full statutory accounts
• In iXBRL format

Example:

• Accounting period ends: 31 March 2025
• CT600 due: 31 March 2026

Capital Allowance Claim Deadline

Capital allowances (for equipment, machinery, etc.) must be claimed within your CT600.

Deadline is the same as the CT600 filing deadline
 (12 months after the accounting period ends)

Missing this deadline can result in lost tax relief.

Payments on Account (Large Companies)

Companies with taxable profits over £1.5 million (divided by number of group companies) must usually pay Corporation Tax in four quarterly instalments:

• During the accounting period
• Rather than after it ends

These rules are complex and often misunderstood — professional advice is strongly recommended.

Companies House Annual Accounts Deadlines

All limited companies must file annual accounts with Companies House, even if dormant.

First Year Accounts

• Due 21 months after incorporation

Ongoing Accounts

• Due 9 months after the accounting reference date

Example:

• Company incorporated: 8 January 2024
• Accounting reference date: 31 August 2025
• First accounts due: 5 January 2026
• Next accounts due: 31 May 2027

Other Key UK Company Tax Dates

Corporation Tax Registration

• Must register with HMRC within 3 months of starting to trade

Confirmation Statement

• Due every 12 months
• Failure to file can lead to:
• Fines for directors
• Company being struck off

VAT Deadlines (If Registered)

• VAT returns and payments due 1 month and 7 days after each VAT quarter

PAYE Deadlines (If You Have Employees)

• Monthly PAYE payments due by the 22nd of the following month

UK Corporation Tax Deadline Summary

What Happens If You Miss a Deadline?

Missing Corporation Tax deadlines can result in:

• Late filing penalties
• Interest on unpaid tax
• HMRC compliance checks
• Director penalties
• Company strike-off (for Companies House failures)

Penalties apply even if no tax is due.

Key Takeaways for UK Business Owners

• Corporation Tax payment and filing deadlines are different
• Deadlines are based on your accounting period
• Companies House and HMRC deadlines are separate
• Large companies may need to pay tax during the year
• Missing deadlines can be costly

Good planning and accurate record-keeping are essential.

Final Thoughts

Understanding and tracking key Corporation Tax dates is vital for keeping your company compliant and financially healthy.

With multiple deadlines across HMRC and Companies House, many business owners benefit from professional support to ensure:

• Returns are filed correctly
• Tax is paid on time
• Reliefs and allowances are not missed

FAQs

When is my company’s Corporation Tax return due?
 The CT600 is due 12 months after the end of your accounting period.

When do I need to pay Corporation Tax?
 Corporation Tax must be paid 9 months and 1 day after the accounting period ends.

What happens if I miss a Corporation Tax deadline?
 You may face penalties, interest, and HMRC investigations — even if no tax is owed.