CT600 vs Self Assessment: What's the Difference? (Company vs Personal Tax)

CT600 vs Self Assessment: What's the Difference?

If you're a company director, you may need to file both a CT600 (company tax return) and a Self Assessment return (personal tax return). Many first-time directors confuse the two — or don't realise they need both.

Here's the definitive guide to how they differ and when you need each one.

Quick Comparison

The CT600: Your Company's Tax Return

The CT600 is filed by your limited company. It reports:

• Company trading profits and losses
• Corporation tax due on those profits
• Capital gains made by the company
• Investment income
• R&D claims, group relief, and other reliefs

Key facts

• Who files: The company (as a legal entity separate from you)
• Tax rate: 19% (small profits) to 25% (main rate)
• Filing deadline: 12 months after the accounting period ends
• Payment deadline: 9 months and 1 day after the accounting period ends
• Accounts required: iXBRL accounts must be submitted with the return

Example

Your company has a year-end of 31 March 2025:

• CT600 filing deadline: 31 March 2026
• Corporation tax payment deadline: 1 January 2026

Self Assessment: Your Personal Tax Return

Self Assessment (SA100) is your personal tax return. As a company director, you report:

• Your salary from the company (PAYE income)
• Dividends received from the company
• Any other personal income (rental, freelance, interest, etc.)
• Personal tax reliefs and allowances

Key facts

• Who files: You as an individual
• Tax rate: 20% basic, 40% higher, 45% additional (plus NI on salary)
• Filing deadline: 31 January after the tax year ends (paper: 31 October)
• Payment deadline: 31 January (plus payments on account 31 July)
• Tax year: 6 April to 5 April (not your company year-end)

Example

For the 2024/25 tax year (6 April 2024 – 5 April 2025):

• Online filing deadline: 31 January 2026
• Payment deadline: 31 January 2026

Do You Need Both?

You ALWAYS need a CT600 if:

• Your company is active (trading or has income)
• Even if the company made zero profit (nil return)
• Even if the company is dormant (dormant CT600)

You need Self Assessment if:

• You're a company director AND receive dividends
• Your total income exceeds £150,000
• You have income from sources other than PAYE
• HMRC has sent you a notice to file
• You have capital gains to report
• You want to claim certain tax reliefs

You might NOT need Self Assessment if:

• Your only income is a PAYE salary below £150,000
• You receive no dividends (unusual for directors)
• HMRC hasn't asked you to file

Important: Most company directors DO need both returns, because the typical structure involves taking a small salary plus dividends — and dividends must be reported on Self Assessment.

How They Interact: The Director's Tax Journey

Here's how the two returns work together in practice:

Step 1: Company earns profits

Your company makes £80,000 profit in the year to 31 March 2025.

Step 2: You take salary + dividends

• Salary: £12,570 (personal allowance, tax-free)
• Employer's NI: ~£880 (deductible expense for the company)
• Dividends: £40,000

Step 3: Company files CT600

• Profit: £80,000
• Less salary + employer's NI: £13,450
• Taxable profit: £66,550
• Corporation tax (19%): £12,644.50
• Profit after tax available for dividends: £53,905.50

Step 4: You file Self Assessment

• Salary: £12,570 (covered by personal allowance)
• Dividends: £40,000
• Less dividend allowance: £500 (2024/25)
• Taxable dividends: £39,500
• Tax at 8.75% (basic rate): up to £37,700 of total income = £2,204
• Tax at 33.75% (higher rate): remaining £2,370 × 33.75% = £800
• Total personal tax: ~£3,004

The combined picture

• Corporation tax: £12,644
• Personal income tax: £3,004
• Employer's NI: £880
• Total tax on £80,000 profit: ~£16,528 (20.7% effective rate)

This is significantly less than if you were self-employed paying income tax and NI directly on £80,000.

Common Mistakes

1. Filing CT600 but forgetting Self Assessment

Your company return is up to date, but you haven't filed your personal return. HMRC will fine you personally — £100 for each day late, escalating.

2. Reporting dividends on the wrong return

Dividends are reported on your Self Assessment, not the CT600. The CT600 only shows the company's profits, not what you took out as dividends.

3. Confusing the tax years

• CT600 follows your company's accounting period (e.g., year to 31 March)
• Self Assessment follows the tax year (6 April to 5 April)
• If your company year-end is 31 December, dividends paid in January-March fall in a different tax year than April-December dividends

4. Double-counting salary

Your salary is:

• An expense on the CT600 (reduces company profit)
• Income on your Self Assessment (you pay personal tax on it) It's not taxed twice — it's an expense for the company and income for you.

5. Missing the payment dates

• Corporation tax: 9 months + 1 day after company year-end
• Self Assessment: 31 January
• These are different dates — mark both in your calendar

Dividend Tax Rates (2024/25)

Filing Timeline for a Typical Director

Assuming company year-end 31 March 2025:

Which One Does Taxpipe Handle?

Taxpipe handles the CT600 — your company's corporation tax return. We file it electronically with HMRC for just £59.

For Self Assessment, you'll need to file separately. You can:

• Use HMRC's free online Self Assessment service
• Use commercial software
• Hire an accountant

Tip: Get your CT600 done first. The company's figures (salary paid, dividends declared, profit after tax) feed into your Self Assessment. Having the CT600 complete makes your personal return easier.

Frequently Asked Questions

Can I file my CT600 and Self Assessment together?

No. They're separate returns filed through different HMRC systems. The CT600 goes through the Corporation Tax Gateway; Self Assessment goes through the SA Gateway.

What if my company year-end is different from the tax year?

That's normal. Most companies don't have a 5 April year-end. Your CT600 covers your company's accounting period; your Self Assessment covers 6 April to 5 April. Dividends are reported in the tax year they're paid.

Do I need an accountant for both?

Not necessarily. A CT600 for a straightforward small company can be filed yourself using Taxpipe. Self Assessment for a director taking salary + dividends is also manageable — HMRC's online tool works well for simple cases.

What happens if I only file one?

HMRC will chase and fine you for whichever one is missing. They cross-reference data between Corporation Tax and Self Assessment, so they know if you're a director who should be filing both.

Start with your company's CT600 — file with Taxpipe for just £59. Then tackle your Self Assessment knowing all the company figures are sorted.

Related Articles

• Company Tax Return (CT600) vs Annual Accounts: What's the Difference?
• CT600 Deadline: When to File Your Corporation Tax Return (and When to Pay)
• 10 Common CT600 Mistakes (and How to Avoid Them)
• CT600 Deadline: When Is Your Company Tax Return Due?