Corporation Tax deadlines
Year-end accounts, CT600, and Corporation Tax payment dates, plus Companies House obligations.
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The three dates every limited company must know
Accounts to Companies House: nine months after your accounting year end. Corporation Tax payment to HMRC: nine months and one day after the end of the accounting period. CT600 return to HMRC: twelve months after the end of the accounting period.
Read that order again — the tax is due before the return is. In practice the accounts and CT600 get prepared together well before the payment date, because you cannot know what to pay without them.
Your first year runs on different dates
A new company's first accounts are due 21 months after incorporation, and its first accounting period often runs slightly longer than 12 months — which splits it into two Corporation Tax periods, two CT600s, and two payment dates.
It is the single most common place new directors get caught, because the dates never look like this again. We map them out for every new company at engagement.
What lateness costs
Companies House penalties for late accounts are automatic and scale with delay — from £150 to £1,500 for a private company, doubled if you are late two years running. A late CT600 starts at £100 and escalates, and late Corporation Tax accrues interest from the due date.
Persistent non-filing has a sharper edge: Companies House can begin striking the company off the register.
How we keep companies clean
Every RR company client's year end, payment date, and filing dates sit in Deadline Lock, tracked with advance notification. Accounts are prepared from reconciled monthly records, so the nine-month window is used for review and tax planning — not for finding the records.
Frequently asked questions
Is Corporation Tax really due before the return?
Yes — payment is due nine months and one day after the period end, while the CT600 is due at twelve months. The accounts and tax computation are prepared early so the payment figure is known well before it leaves the bank.
What is an accounting period?
The period a CT600 covers, normally matching your company's financial year and never longer than 12 months. If your statutory accounts cover more than 12 months — common in year one — HMRC splits it into two accounting periods with separate returns and payment dates.
Can I change my company's year end?
Yes, by filing with Companies House. You can shorten a year end as often as you like, but lengthening is generally restricted to once every five years. Changing the year end moves your accounts, payment, and CT600 dates — so it should be a deliberate decision, not a side effect.
Does a dormant company still have deadlines?
Yes. Dormant companies still file annual accounts (a simplified version) and a confirmation statement with Companies House. HMRC usually agrees to switch off CT600 requirements for a genuinely dormant company — but only after being told.