Accountant vs DIY CT600 Filing: Honest Comparison
Every year, hundreds of thousands of UK limited company directors face the same question: should I pay an accountant to file my CT600, or can I do it myself? The answer isn't the same for everyone — but it's probably simpler than you think.
This guide gives you an honest, side-by-side comparison of using an accountant versus filing your own Company Tax Return. No agenda — just the facts to help you decide.
What's Actually Involved in Filing a CT600
Before comparing approaches, let's be clear about what "filing a CT600" actually means. It's not just filling in one form. The full process includes:
- Preparing your annual accounts — profit and loss, balance sheet
- Converting accounts to iXBRL format — the tagged format HMRC requires
- Completing the CT600 form — entering the correct figures in the right boxes
- Calculating your tax — including marginal relief if applicable
- Claiming reliefs and allowances — capital allowances, losses, R&D credits
- Submitting to HMRC — electronically via the Government Gateway
- Filing accounts with Companies House — a separate but related requirement
An accountant handles all of this. If you're doing it yourself, you need a way to handle each step — which is where filing software comes in.
Cost Comparison
This is usually the main driver. Let's look at real numbers.
Accountant Fees
| Service level | Typical annual cost | What's included |
|---|---|---|
| CT600 only (you provide accounts) | £300–£600 | CT600 completion, iXBRL, submission |
| Full accounts + CT600 | £600–£1,500 | Annual accounts, CT600, iXBRL, submission |
| Full service (bookkeeping + accounts + CT600) | £1,200–£3,000+ | Everything including monthly bookkeeping |
These are typical fees for small limited companies with straightforward affairs. London firms and specialist accountants charge more. If your company has complex transactions, overseas income, or multiple subsidiaries, expect higher fees.
DIY Filing Costs
| Approach | Cost per year |
|---|---|
| Filing software (e.g., TaxPipe) | £50–£200 |
| HMRC online (CT600 only, no iXBRL) | Free, but limited |
The cost difference is stark. Even the most expensive filing software costs a fraction of the cheapest accountant. For a company saving £500–£1,000 per year, DIY filing with software pays for itself many times over.
Over 5 years: An accountant at £800/year costs £4,000. Software at £100/year costs £500. That's £3,500 saved — real money for a small business.
Time Comparison
With an Accountant
Your time commitment:
- Gathering documents: 1–3 hours (bank statements, receipts, invoices)
- Sending to accountant: 30 minutes
- Answering queries: 30 minutes–2 hours (they'll have questions)
- Reviewing and approving: 30 minutes
- Total: 2–6 hours per year
But there's a hidden time cost: waiting. Accountants are busy, especially near filing deadlines. Your return might sit in a queue for weeks. If you're filing close to deadline, this can cause stress and even late filing penalties.
DIY with Software
Your time commitment:
- Gathering documents: 1–3 hours (same as above)
- Entering figures into software: 1–3 hours
- Reviewing and submitting: 30 minutes
- Total: 2–6 hours per year
The total time is similar — but you're in control. You file when you're ready, not when your accountant gets to it. No chasing, no waiting, no last-minute panic.
Expertise: What Do You Actually Need to Know?
This is where many people talk themselves out of DIY filing. "I'm not an accountant — I can't do this." But let's separate myth from reality.
What you DON'T need to know for DIY filing
- Tax legislation chapter and verse
- How to manually tag iXBRL accounts
- The CT600 box numbers and what goes where
- How to calculate marginal relief by hand
- HMRC's submission protocols
Good filing software handles all of this for you. You enter your business figures — revenue, expenses, assets — and the software does the rest.
What you DO need to know
- Your company's income and expenses — you should know these as the director
- Basic categories — is a purchase an expense or an asset?
- Whether anything unusual happened — did you sell a major asset, start a new trade, have overseas income?
- Your allowable expenses — what you can and can't claim
If you run a straightforward small company — providing services, selling products, paying yourself a salary and dividends — you almost certainly have enough knowledge to file yourself.
Risk Comparison
Risks of Using an Accountant
People assume accountants eliminate risk. They reduce it — but don't eliminate it:
- Errors still happen — accountants make mistakes too, especially with high client volumes
- Miscommunication — if you give them incomplete information, the return will be wrong
- You're still responsible — legally, the director is responsible for the Company Tax Return, not the accountant
- Missed deadlines — if your accountant is overloaded, your return might be filed late (and you pay the penalty, not them)
- Generic advice — a busy accountant might not proactively suggest tax savings specific to your situation
Risks of DIY Filing
- Errors in data entry — you might enter a wrong figure (but software validation catches many of these)
- Missing a relief or allowance — you might not know about a claim you're entitled to
- Complex situations — if your company has unusual transactions, you might not handle them correctly
- No professional review — nobody double-checks your work
How Software Mitigates DIY Risks
Modern filing software significantly reduces the risks of self-filing:
- Validation checks catch mathematical errors and common mistakes
- Guided workflows prompt you for reliefs and allowances you might forget
- Automatic calculations mean marginal relief, capital allowances, and tax due are calculated correctly
- iXBRL generation is handled automatically — no manual tagging
- Pre-submission checks flag issues before you send anything to HMRC
The software can't replace all professional judgment — but for straightforward companies, it covers 95% of what you need.
When You Should Use an Accountant
An accountant is worth the money when:
Your company has complex affairs
- Multiple trades or income streams
- Overseas income or international operations
- Group company structures
- R&D tax relief claims (these require detailed supporting evidence)
- Large capital allowances with multiple asset pools
- Share schemes or equity-based compensation
You genuinely don't have time
Some directors are too busy running their business to spend a few hours on filing. If your hourly rate genuinely makes it uneconomical to file yourself, an accountant makes financial sense.
You want proactive tax planning
The real value of a good accountant isn't filing your CT600 — it's advising you on how to structure things tax-efficiently going forward. If you want strategic tax advice, you need a human who knows your business.
You're under HMRC investigation
If HMRC opens an enquiry into your CT600, get professional help immediately. This is not a DIY situation.
When DIY Filing Makes Sense
Filing yourself (with software) is the practical choice when:
You run a straightforward company
- Single trade (services, consulting, contracting, e-commerce)
- UK-only operations
- One or two directors
- Turnover under £1 million
- Simple expense structure
This describes the vast majority of UK limited companies.
You want to save money
If you're a contractor, freelancer, or small business owner operating on tight margins, saving £500–£1,000 per year on accountancy fees makes a meaningful difference.
You want control and speed
No waiting for your accountant. No chasing for updates. File when you're ready, on your own schedule.
You already do your own bookkeeping
If you're already tracking income and expenses (via spreadsheets, Xero, FreeAgent, or similar), you already have the figures you need. The CT600 is essentially a summary of information you already have.
The Middle Ground: Software + Occasional Accountant
Many savvy directors take a hybrid approach:
- File your CT600 yourself using software for routine years
- Consult an accountant when something unusual happens (major asset purchase, restructuring, international expansion)
- Get a one-off review every 2–3 years to check you're not missing anything
This gives you the cost savings of DIY filing with the safety net of professional advice when it actually matters.
Real-World Scenarios
Scenario 1: IT Contractor (Inside IR35)
Company profile: Solo director, £80,000 revenue, salary + dividends, minimal expenses, working from home.
Best approach: DIY with software. This is a textbook simple company. An accountant would charge £600+ to do what takes 2–3 hours with software. Annual saving: ~£500.
Scenario 2: E-commerce Business
Company profile: Two directors, £300,000 revenue, stock, multiple expenses categories, capital purchases.
Best approach: DIY with software for the CT600, with a bookkeeper helping with monthly accounts. The CT600 filing itself is straightforward once accounts are prepared. Annual saving on CT600 filing: ~£400.
Scenario 3: Tech Startup Claiming R&D Relief
Company profile: Three directors, £500,000 revenue, significant R&D spend, wanting to claim R&D tax credits.
Best approach: Accountant. R&D claims require detailed documentation and professional judgment. The potential value of the claim (often tens of thousands of pounds) far outweighs accountancy fees.
How to Start Filing Your Own CT600
If you've decided to go the DIY route:
- Get your documents ready — use our filing checklist
- Choose your software — compare the best CT600 software options
- Sign up and follow the guided process — TaxPipe walks you through every step
- Review before submitting — check figures match your bank statements
- Submit and pay your tax — the software tells you exactly how much and when to pay
First-time filers: read our complete guide to filing your first CT600.
Frequently Asked Questions
Am I legally allowed to file my own CT600?
Absolutely. There's no legal requirement to use an accountant. Any director can file their company's CT600 themselves. You just need to register for the HMRC Government Gateway and authorise your filing software.
What if I make a mistake on my CT600?
You can amend your CT600 within 12 months of the filing deadline. HMRC allows corrections — it's not a one-shot process.
Will HMRC treat me differently if I don't use an accountant?
No. HMRC processes all returns the same way regardless of who prepared them. There's no "DIY penalty" or extra scrutiny for self-filed returns.
Can I switch from an accountant to DIY mid-year?
Yes. Your accountant doesn't own your financial data. Request your records, and you can file your next return yourself. Give reasonable notice if you're ending an ongoing engagement.
What if my accountant files late — who's responsible?
You are. As the company director, you're legally responsible for the CT600 being filed on time, even if you've delegated the work to an accountant. This is one reason some directors prefer DIY — at least if it's late, they know why.
How much can I realistically save by filing myself?
Most small company directors save £400–£1,000 per year by switching from an accountant to software. Over 5 years, that's £2,000–£5,000.
The Bottom Line
There's no universal right answer. But the honest truth is: most small limited company directors don't need an accountant for their CT600. Modern filing software handles the complex parts — iXBRL, calculations, submission — while you provide the figures you already know.
If your company is straightforward, self-filing with software is cheaper, faster, and puts you in control. Save the accountant for when you genuinely need expert advice.
Ready to try filing yourself? Start your CT600 with TaxPipe — it's designed for directors who want to file confidently without the accountant's bill.