Key facts
- The CT600 is the Company Tax Return filed with HMRC for each accounting period.
- It must be accompanied by the company’s statutory accounts and a tax computation, both in iXBRL format.
- The filing deadline is 12 months after the end of the accounting period.
- All CT600 returns must be filed online — HMRC no longer accepts paper returns.
How to File Your CT600 Company Tax Return
The CT600 is HMRC’s Company Tax Return — the form on which a company reports its income, gains, reliefs, and the resulting Corporation Tax liability for an accounting period.[1]
Every company that is active (trading, receiving income, or disposing of assets) must file a CT600 for each accounting period. This includes companies that are active but have no tax to pay (for example, because they made a loss).
The return is filed electronically with HMRC and must be accompanied by:[2]
- The company’s statutory accounts (in iXBRL format)
- A tax computation showing how taxable profits were calculated (also in iXBRL)
- Any supplementary pages relevant to the company’s circumstances
Key Sections of the CT600
The CT600 is divided into several sections. The main ones are:[2]
| Section | What It Covers |
|---|---|
| Company information | Name, UTR, registered number, accounting period dates, type of return |
| Turnover & income | Total turnover, trading profits, investment income, property income |
| Deductions & reliefs | Trading losses, capital allowances, management expenses, group relief, R&D claims |
| Chargeable gains | Gains and losses on asset disposals (requires supplementary page CT600C) |
| Tax calculation | Profits chargeable to CT, rates applied, marginal relief, tax due or repayable |
| Tax payments | Tax already paid, overpayments, amount outstanding |
Supplementary Pages
Depending on the company’s activities, additional pages may be required:
- CT600A — Loans and arrangements to participators (close companies)
- CT600B — Controlled foreign companies
- CT600C — Group and consortium relief, chargeable gains
- CT600D — Insurance and friendly societies
- CT600E — Charities and community amateur sports clubs
- CT600J — Tonnage tax
- CT600L — R&D and creative industry tax credits
The Tax Computation
The tax computation is a separate document that bridges the gap between the company’s accounting profit (as shown in its statutory accounts) and its taxable profit (as reported on the CT600).[2]
A typical computation includes:
- Accounting profit per the financial statements
- Add back disallowable expenses (e.g. entertaining, depreciation, fines)
- Deduct non-taxable income (e.g. dividends from UK companies)
- Deduct capital allowances (replacing depreciation for tax purposes)
- Arrive at adjusted trading profit
- Add other income (investment, property, chargeable gains)
- Deduct reliefs (trading losses, group relief, charges)
- Calculate Corporation Tax at the appropriate rate
iXBRL requirement: Both the statutory accounts and the tax computation must be filed in iXBRL (inline XBRL) format. Most commercial accounting and tax software handles this automatically. You cannot simply upload a PDF.[4] HMRC-recognised software such as GoFile’s CT600 filing tool prepares the iXBRL accounts and computations for you.
How to File
CT600 returns must be filed electronically. HMRC no longer accepts paper Corporation Tax returns.[3] You can file using:
- Commercial software — most accounting packages (Xero, QuickBooks, Sage, etc.) can produce and file CT600 returns directly with HMRC
- HMRC’s free filing service — available for straightforward returns (limited to simpler company structures)
- An accountant or tax agent — your agent can file on the company’s behalf using professional software
Joint filing: You can file your statutory accounts with both HMRC and Companies House at the same time through the “joint filing” service, saving you from submitting accounts separately to each organisation.[3]
Common Mistakes to Avoid
- Wrong accounting period dates — ensure the CT600 dates match the company’s actual accounting period, not the statutory accounts period
- Missing supplementary pages — forgetting to include CT600A for close company loans or CT600L for R&D claims
- Accounts not in iXBRL — the return will be rejected if accounts are not properly tagged
- Not filing when loss-making — a CT600 must be filed even if the company has no tax to pay
- Confusing filing and payment deadlines — the CT600 is due 12 months after the period end, but tax must be paid within 9 months and 1 day
Frequently Asked Questions
What is a CT600?
The CT600 is the Company Tax Return that every active UK company must file with HMRC for each accounting period. It reports the company’s income, gains, reliefs, and the resulting Corporation Tax liability.
Do I need to file a CT600 if my company made a loss?
Yes. Every active company must file a CT600 for each accounting period, even if it has no tax to pay because it made a trading loss or its income is fully relieved.
What format must the CT600 accounts be in?
The statutory accounts and tax computation accompanying the CT600 must be filed in iXBRL (Inline XBRL) format. Most commercial accounting software handles this automatically. PDFs are not accepted.
Can I file a CT600 on paper?
No. HMRC no longer accepts paper Corporation Tax returns. All CT600 returns must be filed electronically, either through commercial software, HMRC’s free filing service, or via an accountant.
What supplementary pages might I need with my CT600?
Common supplementary pages include CT600A for loans to participators (close companies), CT600C for group relief and chargeable gains, CT600E for charities, and CT600L for R&D and creative industry tax credits.
Further Reading
- Filing Deadlines — all the dates you need to know
- iXBRL & Digital Filing — understanding the digital filing requirements
- Amending a CT600 — how to correct mistakes after filing
- Company Accounts Requirements — statutory accounts that accompany the CT600
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Sources
- Company Tax Returns — GOV.UK
- Corporation Tax: Company Tax Return (CT600) — GOV.UK
- File your accounts and Company Tax Return — GOV.UK
- Corporation Tax: filing your return online — GOV.UK