Do I Need to File a CT600? When Your Company Must Submit a Tax Return
Short answer: if you have a UK limited company, you almost certainly need to file a CT600. Even if you made no profit. Even if the company is dormant.
Here's the detail.
Who Must File a CT600?
Every company registered at Companies House that is within the charge to Corporation Tax must file a CT600 Company Tax Return with HMRC.
This includes:
- Active trading companies — obviously
- Companies that made a loss — you still need to report it
- Dormant companies — yes, even if there was zero activity
- Property companies — rental income is chargeable to CT
- Holding companies — even if they only hold shares
- Companies with only bank interest — interest is taxable income
The Only Exceptions
You do NOT need to file a CT600 if:
- Your company has never been active and you've told HMRC it's dormant (they'll confirm you don't need to file)
- Your company is exempt from Corporation Tax (extremely rare — mainly some flat management companies and clubs with very low income)
- HMRC has confirmed in writing that no return is required
If you're unsure, the safe answer is: file it. There's no penalty for filing when you didn't strictly need to, but there ARE penalties for not filing when you should have.
New Companies — When Does the Obligation Start?
When you register a limited company at Companies House:
- HMRC is notified automatically (Companies House shares the data)
- HMRC sends you a CT41G form asking about your company's activities
- You must register for Corporation Tax within 3 months of starting to trade
- Your first CT600 covers the period from incorporation (or start of trading) to your chosen year-end
Important: Even if HMRC hasn't contacted you yet, the obligation exists from the moment your company becomes active.
Read our guide for first-time filers.
Dormant Companies — Yes, You Still Need to File
A dormant company with no transactions must still file a CT600 with HMRC unless HMRC has specifically told you otherwise.
Filing a nil CT600 return confirms to HMRC that:
- The company had no taxable income
- No Corporation Tax is due
- You're still complying with your obligations
Don't confuse CH and HMRC dormancy. A company can be dormant for Companies House purposes (no "significant accounting transactions") but still need to file with HMRC if it received bank interest or had any taxable income.
Companies That Made a Loss
If your company made a trading loss, you must file a CT600 to:
- Report the loss to HMRC
- Claim loss relief (carry forward or carry back)
- Avoid penalties for non-filing
A loss doesn't mean no tax return — it means your tax bill is £0, but HMRC still needs to know.
What Happens If You Don't File?
HMRC takes non-filing seriously:
| Time Late | Penalty |
|---|---|
| 1 day late | £100 |
| 3 months late | Another £100 |
| 6 months late | HMRC estimates your tax + 10% penalty |
| 12 months late | Another 10% of unpaid tax |
Plus: Daily penalties of £10/day can be charged between 3 and 6 months (up to £900). Interest runs on any unpaid tax from the payment deadline.
These penalties apply even if you owe £0 in tax. Filing late with nil liability still triggers the £100 penalties.
Read more about CT600 penalties.
When Is the Filing Deadline?
Your CT600 must be filed within 12 months of the end of your accounting period.
Your Corporation Tax payment is due earlier — within 9 months and 1 day of the period end.
So if your year-end is 31 March 2026:
- Payment deadline: 1 January 2027
- Filing deadline: 31 March 2027
Check your specific CT600 deadline.
What You Need to File
To complete your CT600, you'll need:
- Your UTR (Unique Taxpayer Reference) — 10-digit number from HMRC
- Your CRN (Company Registration Number)
- Your company's accounts (profit & loss, balance sheet)
- iXBRL accounts — tagged accounts in iXBRL format
- Tax computations — how you calculated your tax liability
Use our CT600 filing checklist to make sure you have everything.
Can I File It Myself?
Yes. You don't need an accountant to file a CT600. Since April 2011, all CT600 returns must be filed electronically — but you don't need to use HMRC's own software.
Read our guide on filing a CT600 without an accountant.
How Taxpipe Makes It Simple
Taxpipe asks you straightforward questions about your company and income, then:
- Calculates your Corporation Tax (including FY splitting and marginal relief)
- Generates your iXBRL accounts automatically
- Fills in the correct CT600 boxes
- Submits directly to HMRC
£59 per filing. No subscription. No jargon.