Everything You Need to Know About Corporation Tax in the UK

Corporation tax in the UK is one of the most challenging responsibilities for companies to manage. With changing tax rates, strict deadlines, and complex filing rules, even small mistakes can lead to penalties, cash flow issues, or unnecessary stress for business owners.

If you run a limited company, you are not alone in finding corporation tax confusing or time-consuming. Many businesses struggle to keep track of what they owe, when payments are due, and how to file correctly while also trying to focus on running and growing their company.

This guide brings clarity to the process. Drawing on current UK tax rules, it explains corporation tax, covering up-to-date rates, key deadlines, payment methods, and practical corporation tax support that helps businesses stay compliant, organised, and financially confident.

What Is Corporation Tax?

Corporation Tax is a tax charged on the profits made by UK companies. It applies to:

• UK limited companies
• Foreign companies with a permanent presence in the UK
• Clubs, societies, and associations that generate taxable income

Tax is paid on profits after allowable business expenses, reliefs, and capital allowances have been deducted.

What Counts as Taxable Profit?

Taxable profit usually includes:

• Trading profits from day-to-day business activity
• Investment income such as interest
• Capital gains from selling business assets

Allowable expenses can reduce your tax bill. These include staff costs, office expenses, professional fees, and certain equipment costs.

UK Corporation Tax Rates (2025 to 2026)

The UK uses a tiered corporation tax system based on profit levels.

Corporation Tax Rates Table

Annual Profits	Corporation Tax Rate
£50,000 or less	19%
£50,001 to £250,000	Between 19% and 25%
Over £250,000	25%

Companies with profits between £50,000 and £250,000 benefit from marginal relief. This reduces the effective tax rate so it increases gradually rather than jumping straight to 25%

Patent Box Rate

Companies earning profits from patented inventions may qualify for a reduced effective tax rate of 10% under the Patent Box regime, subject to conditions.

Corporation Tax Deadlines You Must Know

There are two separate deadlines. One for paying the tax and one for filing the tax return.

Corporation Tax Payment Deadline

Most companies must pay corporation tax within nine months and one day after the end of their accounting period.

Example

If your accounting year ends on 31 March 2025, your corporation tax payment is due by 1 January 2026.

Corporation Tax Return Deadline (CT600)

The CT600 return must be submitted within twelve months after the end of the accounting period.

Using the same example above, the CT600 must be filed by 31 March 2026.

Corporation Tax Deadlines at a Glance

Accounting Period End	Tax Payment Due	CT600 Filing Due
31 March 2025	1 January 2026	31 March 2026
30 June 2025	1 April 2026	30 June 2026
30 September 2025	1 July 2026	30 September 2026
31 December 2025	1 October 2026	31 December 2026

Special Rules for Large Companies

Companies with profits over £1.5 million usually cannot pay corporation tax in one lump sum.

Instead, they must pay through quarterly instalment payments.

Quarterly Instalment Overview

Instalment	When It Is Due
First	Six months and thirteen days after the start of the accounting period
Second	Three months after the first instalment
Third	Three months after the second instalment
Final	Three months and fourteen days after the end of the accounting period

Very large companies with profits above £20 million may have earlier payment schedules.

How to Pay Corporation Tax

Corporation Tax must be paid electronically. Accepted payment methods include:

• Online or telephone banking
• Faster Payments
• BACS bank transfer
• CHAPS same-day transfer
• Direct Debit
• Corporate debit or credit card

Always use your unique 17-character corporation tax payment reference so HMRC can match the payment correctly.

What Happens If You Miss a Deadline?

Late Payment

Interest is charged automatically from the day after the payment deadline until the tax is paid in full.

Late Filing Penalties

Delay Length	Penalty
One day late	£100
More than three months	Additional £100
More than six months	10% of unpaid tax
More than twelve months	A further 10% of unpaid tax

Repeated late filing increases fixed penalties.

Corporation Tax Solutions for UK Businesses

Managing corporation tax does not have to be stressful. The right solutions can save time, reduce errors, and improve cash flow.

Accounting Software

Most companies now use commercial accounting software to prepare and submit corporation tax returns. This is especially important because HMRC’s free online CT600 filing service closes on 31 March 2026.

Benefits include:

• Automatic profit calculations
• Built-in deadline reminders
• Direct online submission to HMRC
• Better record keeping throughout the year

Professional Corporation Tax Support

Accountants provide valuable corporation tax support for businesses with:

• Marginal relief calculations
• Quarterly instalment requirements
• Research and development claims
• Patent Box claims
• Group company structures

Professional advice can reduce risk and help businesses claim all available reliefs legally.

HMRC Online Business Tax Account

Every company should maintain an HMRC business tax account. It allows you to:

• View Corporation Tax liabilities
• Check payment history
• Set up Direct Debit
• Receive official HMRC messages

This helps businesses stay organised and avoid missed deadlines.

Case Study Example

Small Company

• Annual profit: £40,000
• Corporation Tax rate: 19%
• Tax payable: £7,600
• Payment due: Nine months and one day after year-end
• Filing due: Twelve months after year-end

Growing Company

• Annual profit: £180,000
• Marginal relief applies
• Effective tax rate between 19 and 25%
• Requires careful calculations to avoid overpaying

Using accounting software and professional advice helped both companies meet deadlines and avoid penalties.

How Apex Accountants Helps with Corporation Tax in the UK

Managing corporation tax correctly is essential for the financial health and compliance of any UK company. With changing tax rules, strict deadlines, and increasing digital requirements, many businesses find it difficult to keep up while also focusing on growth.

Apex Accountants provides clear, reliable, and proactive corporation tax solutions designed around your business needs. We handle everything from accurate profit calculations and CT600 submissions to deadline management and tax planning, ensuring nothing is missed. Our approach combines up-to-date accounting technology with hands-on professional expertise, giving you clarity, confidence, and control over your tax position. By choosing Apex Accountants, you reduce the risk of penalties, improve cash flow planning, and gain a trusted advisor who understands your business. If you want expert support with your corporation tax and a partner you can rely on, contact Apex Accountants today to find out how we can help.