Business Tax Return UK: Limited Company Guide

If you run a UK limited company, your "business tax return" is called a Company Tax Return (CT600). This guide explains what it is, when to file, and how to submit it to HMRC.

What Is a Business Tax Return for a Limited Company?

A business tax return for a limited company is officially called a Company Tax Return or CT600. It's the form you submit to HMRC to report:

Your company's income and expenses
Your taxable profit
How much corporation tax you owe

Important: If you're a sole trader, you don't file a CT600. Instead, you report business income on your personal Self Assessment tax return.

Who Needs to File a Company Tax Return?

All UK limited companies must file a Company Tax Return, including:

Active trading companies
Investment companies
Dormant companies (simplified return)
Companies that made a loss
Companies with no tax to pay

Even if your company has no activity, you still need to file—unless it's been officially dormant since incorporation.

Business Tax Return Deadlines

Your company has its own accounting period, and deadlines are based on when that period ends:

Action	Deadline
File Company Tax Return	12 months after accounting period ends
Pay corporation tax	9 months and 1 day after accounting period ends

Example: For a year ending 31 December 2024:

Filing deadline: 31 December 2025
Payment deadline: 1 October 2025

Notice that you pay tax before you need to file. Many directors miss this and file first, then pay late.

What You Need to File

To complete your business tax return, you'll need:

Financial Information

Turnover (total sales)
Cost of sales
Operating expenses
Director remuneration
Other income (interest, investments)

Supporting Documents

Company accounts (profit and loss, balance sheet)
Tax computations (how you calculated taxable profit)
Capital allowances schedule (if claiming)

Company Details

Company registration number
Unique Taxpayer Reference (UTR)
Accounting period dates
Company type

How to File Your Business Tax Return

You can file your Company Tax Return:

1. Using Commercial Software (Recommended)

HMRC-recognised software like TinyTax lets you:

Complete your CT600 online
Calculate tax automatically
Submit directly to HMRC
Generate required iXBRL accounts

2. Using HMRC Online Services

You can file through HMRC's website, but you'll need to:

Prepare your accounts separately
Convert them to iXBRL format
Upload alongside your CT600

3. Through an Accountant

An accountant can prepare and file on your behalf, though this adds cost.

Step-by-Step Filing Process

Gather your figures - Income, expenses, adjustments
Prepare accounts - Profit and loss, balance sheet
Calculate taxable profit - Accounting profit plus/minus tax adjustments
Complete CT600 - Transfer figures to the correct boxes
Submit to HMRC - Via software or HMRC online
Pay your tax - Before the payment deadline

See our detailed guide on how to file your company tax return.

Common Business Tax Return Mistakes

1. Missing the Payment Deadline

Payment is due before filing. Many directors file on time but pay late, incurring interest charges.

2. Wrong Accounting Period

Your CT600 must match your accounting period exactly. If you've changed your year-end, make sure you file for the correct dates.

3. Forgetting Tax Adjustments

Accounting profit isn't always the same as taxable profit. Common adjustments include:

Depreciation (add back)
Capital allowances (deduct)
Entertaining costs (add back)
Fines and penalties (add back)

4. Not Claiming All Expenses

Make sure you claim all legitimate business expenses. Common missed deductions:

Use of home as office
Professional subscriptions
Training costs
Bank charges

5. Incorrect Company Type

Select the right company type on the CT600—micro-entity, small, or medium-sized affects what accounts you can file.

Corporation Tax Rates

Once you've calculated your taxable profit, apply the correct rate:

Profit Level	Tax Rate
Up to £50,000	19%
Over £250,000	25%
£50,001 to £250,000	Marginal relief (effective rate 19-25%)

Learn more about current company tax rates.

Late Filing Penalties

Miss your deadline and HMRC charges penalties:

How Late	Penalty
1 day	£100
3 months	Another £100
6 months	10% of unpaid tax (min £300)
12 months	Another 10% of unpaid tax (min £300)

That's potentially £200 in fixed penalties plus 20% of your tax bill for being a year late.

Business Tax Return vs Personal Tax Return

Feature	Company Tax Return (CT600)	Self Assessment
Who files	Limited companies	Individuals, sole traders
Tax paid	Corporation tax	Income tax
Deadline	12 months after year end	31 January following tax year
Filed with	HMRC	HMRC

If you're a company director, you may need both—a CT600 for your company and Self Assessment for your personal income.

First-Time Filing?

Filing your first business tax return can feel daunting. Our guide for first company tax returns walks you through everything new directors need to know.

File Your Business Tax Return with TinyTax

TinyTax makes filing your Company Tax Return simple. Generate your CT600, accounts, and tax computations in one place—affordably.

File your company tax return with TinyTax →