How to File a Corporation Tax Return
How to file your corp tax return (CT600) with HMRC. Step-by-step guide for UK limited companies.
Corp Tax Return: How to File Your CT600
Your corp tax return—officially called a Company Tax Return or CT600—is how you report your company's profits and pay corporation tax to HMRC. Here's how to file it.
What Is a Corp Tax Return?
A corp tax return is the annual tax filing every UK limited company must submit to HMRC. It reports:
- Your company's income
- Allowable expenses
- Taxable profit
- Corporation tax owed
Who Needs to File?
Every UK limited company must file a corp tax return, including:
- Trading companies
- Property companies
- Investment companies
- Dormant companies
- Companies that made a loss
- Companies with no tax to pay
Filing Deadline
Your corp tax return is due 12 months after the end of your accounting period.
| Accounting Year End | Filing Deadline |
|---|---|
| 31 March 2024 | 31 March 2025 |
| 31 December 2024 | 31 December 2025 |
| 30 June 2025 | 30 June 2026 |
What You Need to File
Company Information
- Company name and registration number
- Unique Taxpayer Reference (UTR)
- Accounting period dates
- Registered office address
Financial Figures
- Turnover
- Cost of sales
- Gross profit
- Administrative expenses
- Director remuneration
- Other operating income
- Net profit
Supporting Documents
- Company accounts (profit and loss, balance sheet)
- Tax computations (showing how taxable profit was calculated)
- Capital allowances schedule (if claiming)
How to File Your Corp Tax Return
Option 1: Tax Software (Recommended)
Software like TinyTax lets you:
- Enter your figures once
- Generate accounts automatically
- Calculate corporation tax
- Submit directly to HMRC
Option 2: HMRC Online Services
You can file through HMRC's website, but you'll need to:
- Prepare accounts in iXBRL format separately
- Upload them with your CT600
- Handle more technical requirements
Option 3: Accountant
An accountant can prepare and file for you. This adds cost but provides professional review.
Step-by-Step Filing Process
1. Gather Your Figures
Collect all income and expense figures for the accounting period. You'll need:
- Bank statements
- Invoices (sales and purchases)
- Payroll records
- Asset purchases
2. Calculate Taxable Profit
Start with your accounting profit and make tax adjustments:
| Adjustment | Action |
|---|---|
| Depreciation | Add back |
| Capital allowances | Deduct |
| Entertainment | Add back |
| Fines/penalties | Add back |
3. Apply the Tax Rate
| Profit Level | Rate |
|---|---|
| Up to £50,000 | 19% |
| £50,001-£250,000 | 19-25% (marginal relief) |
| Over £250,000 | 25% |
4. Complete the CT600
Transfer your figures to the correct boxes. Key boxes include:
- Box 145: Turnover
- Box 155: Gross profit
- Box 165: Expenses
- Box 185: Taxable profit
- Box 475: Corporation tax due
5. Attach Accounts and Computations
Your submission must include:
- Full company accounts (iXBRL format)
- Tax computations showing your calculation
6. Submit to HMRC
File electronically via your chosen software or HMRC online.
Common Mistakes to Avoid
Missing the Payment Deadline
Tax is due 3 months before filing. Many directors file on time but pay late.
Using the Wrong Period
Make sure your CT600 period matches your accounts exactly.
Forgetting Adjustments
Accounting profit ≠ taxable profit. Don't forget to:
- Add back depreciation
- Claim capital allowances
- Adjust for disallowable expenses
Wrong Company Type
Select micro-entity, small, or medium-sized correctly—it affects what accounts you can file.
Late Filing Penalties
| How Late | Penalty |
|---|---|
| 1 day | £100 |
| 3 months | Another £100 |
| 6 months | 10% of tax (min £300) |
| 12 months | Another 10% (min £300) |
Corporation Tax Rates
Current rates (from April 2023):
| Profit | Rate |
|---|---|
| ≤£50,000 | 19% |
| >£250,000 | 25% |
| Between | Marginal relief applies |
After Filing
Once HMRC processes your return, you'll receive:
- Confirmation of receipt
- Any queries (if information is missing)
- Notice of penalties (if late)
File Your Corp Tax Return with TinyTax
TinyTax makes filing your CT600 simple. Enter your figures, we generate your accounts and computations, then file directly to HMRC—affordably.
File your corp tax return with TinyTax →
Related Guides
- Company Tax Return: Complete Guide
- How to File Your Company Tax Return
- Corporation Tax Explained
- Company Tax Rate UK
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