More UK company directors than ever are filing their own CT600 returns — and saving hundreds of pounds in the process.

If your company has straightforward finances (no complex group structures, no R&D claims, no overseas income), you can absolutely file your Corporation Tax return yourself. Here's exactly how.

Who can file their own CT600?

You don't need to be an accountant. If your company fits any of these descriptions, self-filing is realistic:

Sole director/shareholder with a simple trading business
Freelancer or contractor operating through a limited company
Property company with rental income
Dormant company with no trading activity
Micro-entity (turnover under £632,000, balance sheet under £316,000, fewer than 10 employees)

These cover the vast majority of UK limited companies. HMRC estimates over 200,000 company directors file their own returns each year.

What you'll need before you start

Gather these before you begin — it makes the process much faster:

Financial figures

Total turnover (sales/revenue) for the period
Total expenses broken down by category (rent, salaries, travel, professional fees, etc.)
Any capital purchases (equipment, vehicles, computers)
Bank interest earned (even if it's £3.47)
Director's salary and dividends paid
Corporation tax payments already made (payments on account)

Documents

Bank statements for the accounting period
Purchase invoices and receipts
Sales invoices
Payroll records (if you run PAYE)

Step-by-step: filing your CT600

Step 1: Calculate your taxable profit

Start with your total income and subtract allowable business expenses:

Turnover (what you billed/earned) minus Cost of sales (direct costs of delivering your service/product) minus Operating expenses (rent, utilities, insurance, travel, professional fees) minus Staff costs (salaries, employer's NI, pension contributions) equals Trading profit

Then adjust for things that aren't tax-deductible:

Entertainment of clients (not deductible)
Depreciation (replaced by capital allowances)
Personal expenses put through the company

Step 2: Calculate capital allowances

If you bought equipment, computers, or vehicles during the period, you can't just deduct the full cost as an expense. Instead, you claim capital allowances:

Annual Investment Allowance (AIA): Claim 100% of the cost of most plant and machinery, up to £1 million per year
Full expensing: For companies, 100% first-year relief on qualifying plant and machinery (from April 2023)
Cars: Different rules apply — typically 6% or 18% writing down allowance depending on CO2 emissions

Add your capital allowances to your expense deductions.

Step 3: Work out your Corporation Tax

Apply the correct rate to your taxable profits:

Profit level	Rate	Tax year
Up to £50,000	19% (small profits rate)	2023/24 onwards
£50,001 – £250,000	Marginal relief applies	2023/24 onwards
Over £250,000	25% (main rate)	2023/24 onwards

If you have associated companies, the thresholds are divided by the number of associated companies.

Marginal relief formula: Fraction × (Upper limit – Augmented profits) × (Taxable profits / Augmented profits)

The fraction is 3/200. Don't worry — CT600 software calculates this automatically.

Step 4: Prepare iXBRL accounts

Since 2011, HMRC requires company accounts to be submitted in iXBRL (inline eXtensible Business Reporting Language) format alongside the CT600. You can't just attach a PDF.

This is the part where most people give up and hire an accountant. iXBRL requires:

Correct XBRL tags for every financial figure
Valid taxonomy references (FRS 102, FRS 105)
Proper XML structure

This is where CT600 software pays for itself. Tools like Taxpipe generate your iXBRL accounts automatically from the figures you enter — no technical knowledge needed.

Step 5: Submit to HMRC

You need to submit via HMRC's Government Gateway using their XML API. You can't email or post a CT600 anymore.

Options:

HMRC's free filing tool — closing March 2026, clunky interface, no iXBRL generation
Commercial filing software — handles iXBRL, error checking, and submission in one flow
Your accountant's software — what they use if you hire one

Step 6: Pay your Corporation Tax

Filing and paying are separate. After filing your CT600, pay the tax owed by the deadline (usually 9 months and 1 day after your accounting period ends).

Payment methods:

Online banking (same day)
Direct Debit (3 working days)
CHAPS (same day)
Bacs (3 working days)

The payment reference is your UTR followed by the accounting period end date (e.g., 1234567890A2503 for period ending March 2025).

Common mistakes when self-filing

1. Wrong accounting period dates

Your CT600 dates must match exactly what HMRC has on file. If they don't, your return will be rejected. Check your UTR letter or call HMRC to confirm.

2. Forgetting to adjust for disallowable expenses

Client entertaining, personal expenses, and depreciation must be added back to your profit figure. Miss these and you'll underpay tax — HMRC will notice.

3. Not claiming all allowable expenses

Many directors miss legitimate deductions: use of home as office (simplified £6/week or actual costs), professional subscriptions, training courses directly related to your trade.

4. Ignoring the payment deadline

Filing deadline and payment deadline are different:

Filing: 12 months after the accounting period ends
Payment: 9 months and 1 day after the accounting period ends

Miss the payment deadline and you'll pay interest from day one, plus potential penalties.

5. Submitting accounts in the wrong format

HMRC requires iXBRL. A PDF or Excel spreadsheet will be rejected. Use software that generates iXBRL automatically.

How much does an accountant charge for a CT600?

For a simple company, typical accountant fees are:

Service	Cost
Annual accounts preparation	£300 – £600
CT600 filing	£200 – £400
Bookkeeping (monthly)	£50 – £200/month
Total annual cost	£800 – £3,000+

For a micro-entity with simple finances, you're paying £500-1,000+ for something that takes an accountant about 2 hours.

When you SHOULD use an accountant

Self-filing isn't for everyone. Consider an accountant if:

Your company has complex group structures
You're claiming R&D tax credits (the rules are intricate and HMRC scrutinises claims)
You have overseas income or operations
You're dealing with a tax investigation
Your company has significant investment income
You need advice on tax planning or restructuring

For everything else, modern CT600 software makes self-filing straightforward.

How Taxpipe makes it easy

Taxpipe was built specifically for company directors who want to file their own CT600 without the complexity:

Plain-English questions — no accounting jargon, no HMRC box numbers
Automatic tax calculation — including marginal relief, capital allowances, and financial year splits
iXBRL accounts included — generated automatically in the correct format
Direct HMRC submission — filed through Government Gateway, confirmation receipt included
£59 one-time fee — no subscription, no hidden costs, 100% money-back guarantee

The whole process takes about 15 minutes.

File your CT600 for £59 →

Summary

Filing your own CT600 is achievable if your company has straightforward finances. You need your UTR, financial figures, and software that handles iXBRL generation and HMRC submission.

The main barriers — iXBRL formatting and Government Gateway submission — are technical problems that software solves completely. The actual tax calculation for a simple company is straightforward arithmetic.

Save £500+ and file your own Corporation Tax return. Your accountant won't tell you it's this easy.

Freelancer? Corporation Tax Guide for Freelancers →

Free CT600 Filing Software: Your Options in 2026

How to Use HMRC Government Gateway to File Your CT600

How to File Your CT600 Without an Accountant — Complete Guide