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

The official form is called the CT600, but it's commonly known as a corporation tax return, company tax return, or corp tax return.

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

Even if your company had no activity, you still need to file.

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

Payment deadline: Corporation tax is due earlier—9 months and 1 day after your year end.

What You Need to File

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 @AdamsWinter lets you:

Enter your figures once
Generate accounts automatically
Calculate corporation tax
Submit directly to HMRC

This is the fastest and most reliable method for most companies.

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)

A 12-month delay could cost £200 + 20% of your tax bill.

Corporation Tax Rates

Current rates (from April 2023):

Profit	Rate
≤£50,000	19%
>£250,000	25%
Between	Marginal relief applies

See our company tax rate guide for more details.

After Filing

Once HMRC processes your return, you'll receive:

Confirmation of receipt
Any queries (if information is missing)
Notice of penalties (if late)

Keep records for at least 6 years after the accounting period ends.

File Your Corp Tax Return with @AdamsWinter

@AdamsWinter 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 @AdamsWinter →

Company Tax Return: Complete Guide
How to File Your Company Tax Return
Corporation Tax Explained
Company Tax Rate UK

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