How to File Your Corporation Tax Return (CT600)
Complete guide to preparing and filing your CT600 Corporation Tax return with HMRC. Includes what to include and how to calculate your tax.
What You'll Need
- Complete accounting records for the period
- Bank statements (reconciled)
- Purchase invoices for capital allowances
- Prior year accounts
- HMRC Government Gateway login
Step-by-Step Guide
Common Mistakes to Avoid
Missing the payment deadline (it's earlier than filing)
Not claiming all available capital allowances
Forgetting to add back disallowable expenses
Not checking for marginal relief eligibility
Frequently Asked Questions
When is my Corporation Tax return due?
Your CT600 must be filed within 12 months of the end of your accounting period. However, the Corporation Tax payment itself is due 9 months and 1 day after your accounting period ends. Late filing incurs automatic penalties starting at £100.
Can I file my Corporation Tax return myself?
Yes, you can file your CT600 yourself using HMRC-recognised software. You will need your company accounts, details of all income and expenses, and any capital allowances. Many small company directors use accounting software to generate and file the return.
What expenses can I deduct on my Corporation Tax return?
You can deduct all expenses incurred wholly and exclusively for business purposes. This includes staff costs, office rent, equipment, travel, professional fees, and marketing. Capital items like computers are claimed through capital allowances rather than as direct expenses.
What is the Corporation Tax rate for small companies?
Companies with profits under £50,000 pay the small profits rate of 19%. Profits between £50,000 and £250,000 benefit from marginal relief. Companies with profits over £250,000 pay the main rate of 25%.
What happens if I file my Corporation Tax return late?
Late filing penalties are automatic: £100 if one day late, another £100 if three months late, and HMRC estimates your tax bill after six months. After 12 months, an additional penalty of 10% of the unpaid tax is applied. Interest also accrues on any late payment.
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