Year-end accounts and CT600
When year-end accounts and Corporation Tax are due, and how to complete the CT600 company tax return.
Articles
Corporation Tax deadlines
When CT600 returns and Corporation Tax payments are due. Filing deadline is 12 months after period end; payment is 9 months and 1 day.
CT600 guide
How to complete and file your company tax return. What goes in each section and the most common mistakes to avoid.
What is Corporation Tax?
Corporation Tax is the tax companies pay on profits. Here is how the rates and bands work from April 2023 onwards.
Corporation Tax Loss Relief Guide
Corporation Tax loss relief and carry-back rules in the UK: Section 37 claims, 1-year carry-back tax refunds, post-2017 loss flexibility, and terminal loss relief.
UK Corporation Tax rates 2026/27: how the 19% / 25% bands and marginal relief actually work
Corporation Tax is 19% on profits up to £50,000, 25% above £250,000, and tapered between via marginal relief for 2026/27. Full mechanics, worked examples, and the associated company trap.
R&D tax credits 2026/27: the merged scheme, ERIS, and how to claim what your company is owed
Since 1 April 2024 UK R&D tax relief runs on two tracks: the merged RDEC scheme at 20% expenditure credit for most claimants, and ERIS at an 86% additional deduction + 14.5% payable credit for R&D-intensive loss-making SMEs (30%+ intensity threshold).
Director's loan account explained: s455 tax (35.75% from April 2026), beneficial loan benefit-in-kind, and how to clear a DLA safely
A Director's Loan Account (DLA) tracks money flowing between you and your company. Get it wrong and you face 35.75% s455 tax for loans on or after 6 April 2026, plus benefit-in-kind on loans over £10,000. Here is how it actually works and how to clear it.
What is a CT600, and how is it different from annual accounts?
A CT600 is the Company Tax Return sent to HMRC. It reports the company's Corporation Tax position for an accounting period: the taxable profit or loss, the tax due, and the calculation behind it. It is not the same document as the annual accounts.
Annual accounts are prepared for Companies House and show the company's financial position. The CT600 is prepared for HMRC and starts from those accounts, then applies the tax rules. A company can have a profit in its accounts but a different taxable profit once allowable costs, reliefs, and other tax adjustments are considered.
Official guidance: GOV.UK: Company Tax Returns
When are accounts, Corporation Tax, and the CT600 due?
For most private limited companies, annual accounts are due at Companies House nine months after the financial year ends. Corporation Tax is usually due nine months and one day after the end of the Corporation Tax accounting period. The CT600 filing deadline is usually twelve months after that period ends.
These are three separate obligations with different recipients and dates. Paying the tax does not replace the CT600, and filing the CT600 does not replace the Companies House accounts. The accounting period is normally the same twelve months as the financial year, but it can differ, particularly in a company's first year.
Official guidance: GOV.UK: accounts and tax returns for private limited companies
What needs to be prepared before you file?
Start with complete annual accounts and the records that support them: sales, purchases, payroll, bank reconciliations, asset purchases, director transactions, and any claims or reliefs. The CT600 calculation should explain how the accounting profit became the taxable profit. That is the evidence HMRC needs if it asks about a figure later.
The practical risk is not the form itself. It is filing from incomplete records, treating a personal cost as a company cost, or discovering an adjustment after the payment date has passed. Closing the books before the deadline gives the director time to understand the tax position rather than simply react to it.
Do you still file when there is a loss or no tax to pay?
If HMRC has issued a notice to deliver a Company Tax Return, the company must submit it even when it made a loss or has no Corporation Tax to pay. A nil bill is not a reason to leave the return outstanding.
A loss can still matter because it may affect the company's tax position in another period. The return is the formal record of that position. File the return on time and keep the supporting records together, rather than assuming a quiet year needs no action.
Official guidance: GOV.UK: Company Tax Returns
How RR keeps the year-end process under control
For RR company clients, the Evidence Pack keeps the underlying records organised through the year. We use the accounts to establish the tax position early, then Deadline Lock tracks the Companies House, payment, and CT600 dates separately.
That does not change the director's legal responsibility for the filings. It gives the company a clear process, evidence behind the figures, and time to deal with questions before a deadline becomes a problem.
Frequently asked questions
Do I file the CT600 with Companies House?
No. The CT600 is the Company Tax Return for HMRC. Annual accounts go to Companies House. They use related information, but they are separate filings.
When is Corporation Tax paid?
It is usually due nine months and one day after the end of the Corporation Tax accounting period. The CT600 return is usually due later, at twelve months after the period ends.
Can I leave the CT600 until after I have paid the tax?
You can pay before the CT600 deadline, but the return still has its own filing deadline. Paying Corporation Tax does not remove the requirement to file a Company Tax Return when HMRC has issued a notice to deliver one.
Is a CT600 the same as a Corporation Tax calculation?
No. The calculation works out the taxable profit and Corporation Tax due. The CT600 is the return submitted to HMRC that reports that position and other required information.