Corporation Tax is a fundamental aspect of running a business in the UK, and ensuring you meet your obligations is crucial for maintaining compliance and avoiding costly penalties. Whether you’re a new start-up or an established business, understanding the intricacies of Corporation Tax and the importance of submitting your Corporation Tax Return (CT600) on time is essential.
This guide provides clear, detailed insights into what Corporation Tax is, who is required to pay it, and how to navigate the process of registration and filing with HMRC. With expert tips and key deadlines, you’ll be equipped to handle your tax responsibilities with confidence and efficiency.
What is Corporation Tax?
Corporation Tax is a government levy on the profits made by UK-based limited companies and certain other types of organisations. Unlike sole traders who pay Income Tax through Self Assessment, limited companies are liable for Corporation Tax on their net profits, that is, revenue after deducting allowable business expenses.
Whether your company is trading goods, offering services, or investing in property, any profit generated will likely be subject to Corporation Tax.
Who Pays Corporation Tax?
Corporation Tax is payable by a range of business entities. These include:
- UK-registered limited companies
- Clubs and associations (e.g, sports clubs, housing associations, and trade bodies)
- Co-operatives and unincorporated associations conducting business
If you’re a sole trader or part of a traditional partnership, you don’t pay Corporation Tax. Instead, you report your business income via Self Assessment and pay Income Tax and National Insurance.
Do You Need to Register for Corporation Tax?
Yes, if you’re launching a new limited company, you must register for Corporation Tax within 3 months of starting to trade. “Trading” doesn’t just mean selling; it includes actions such as:
- Buying products or stock
- Advertising or marketing your services
- Hiring staff
- Renting business premises
How to Register:
- Log in to your HMRC business tax account
- Use your Government Gateway ID
- Provide your Unique Taxpayer Reference (UTR)
Failing to register on time could result in HMRC imposing penalties, even if your company hasn’t made a profit yet.
What is a Corporation Tax Return?
A Corporation Tax Return, also known as a Company Tax Return or CT600, is the formal submission to HMRC that declares your company’s income, profits, and any Corporation Tax owed.
It typically includes:
- The CT600 form
- Your company’s statutory accounts
- A detailed tax computation
- Any additional documentation HMRC may request
Even if your company hasn’t made a profit, you’re still legally obliged to submit a return unless the company is officially registered as dormant with HMRC.
How to File or Submit a Corporation Tax Return?
When it’s time to file your return, you’ve got a few options:
- Online via HMRC: The most direct route using the Government Gateway portal
- Through an accountant: A good choice if you want to ensure accuracy and compliance
- Using approved third-party software: Many digital accounting platforms integrate CT600 filing tools
You must file even if your company made a loss unless it’s formally registered as dormant.
When Do You Pay Corporation Tax in the UK?
You must pay your Corporation Tax no later than 9 months and 1 day after the end of your company’s accounting period (also known as your financial year).
Example:
- Accounting year end: 31 March 2025
- Corporation Tax payment due: 1 January 2026
You must pay your Corporation Tax before you submit your Corporation Tax Return.
Deadline for Corporation Tax Return
The deadline to submit your Corporation Tax Return (CT600) is 12 months after the end of your accounting period.
Example:
- Accounting period ends: 31 March 2025
- Corporation Tax Return due: 31 March 2026
Filing late results in automatic penalties:
- £100 if you’re up to 1 day late
- Another £100 if still late after 3 months
- Further penalties apply if more than 6 or 12 months late, including a 10% surcharge on unpaid tax
Corporation Tax Rates for 2025/26
The Corporation Tax rate you pay depends on your company’s annual profits:
| Profit Bracket | Tax Rate |
| £0 – £50,000 | 19% |
| £50,001 – £250,000 | 19–25% (with Marginal Relief) |
| Over £250,000 | 25% |
If your business has associated companies (e.g. subsidiaries), these thresholds may be reduced, meaning you’ll reach higher tax bands more quickly.
How to Calculate and Reduce Your Corporation Tax Bill?
There are several legal ways to reduce your Corporation Tax liability:
- Pay yourself a director’s salary (counts as a deductible business expense)
- Make employer pension contributions
- Deduct all allowable business expenses
- Claim Marginal Relief if your profits fall between £50,000 and £250,000
How to calculate Marginal Relief:
- Use HMRC’s Marginal Relief Calculator
- Or better yet, consult an accountant to ensure your tax calculations are correct and optimised
What if Your Company is Dormant or Makes a Loss?
Even if your company made a loss, you are usually still required to file a Corporation Tax Return.
However, if your company is officially dormant, you won’t need to file but you must inform HMRC of the company’s dormant status in advance.
Failing to notify HMRC can result in unnecessary filing obligations and potential fines.
Paying Your Corporation Tax Bill
You can pay your Corporation Tax bill in several convenient ways:
- 💻 Online via HMRC’s website
- 🏦 Bank transfer or direct debit
- ☎️ Telephone banking
Always include your 17-digit Corporation Tax payment reference so that HMRC can correctly attribute the payment.
Payments must clear on time, so allow at least 3 working days when using bank transfers.
What Happens if You Miss the Deadline?
If you miss a payment or filing deadline, HMRC will apply penalties and interest:
- Late payment: Charged at the base rate + 2.5%
- Late filing: Starts at £100, with escalating fines for prolonged delays
Struggling to Pay?
Contact HMRC as soon as possible, they may offer a Time to Pay Arrangement, allowing you to spread the cost over several months.
Summary & Key Deadlines
| Task | Deadline |
| Pay Corporation Tax | 9 months + 1 day after accounting period end |
| Submit Corporation Tax Return | 12 months after accounting period end |
| File annual accounts (Companies House) | 9 months after year-end |
In simple terms, a Corporation Tax Return (CT600) is a document that UK limited companies must file with HMRC, reporting their profits and the tax owed. It’s due 12 months after the end of your company’s accounting period, while the Corporation Tax payment itself is due 9 months and 1 day after the period ends. All active companies must file, even if they make a loss.
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