Corporation Tax is one of those obligations that quietly follows every UK limited company around, and unlike Self Assessment it does not come with a single fixed date everyone remembers. Every company has its own deadline based on its own accounting period, which means two businesses set up a month apart can have completely different filing and payment dates. Getting familiar with your own dates, rather than assuming they match your VAT or payroll calendar, is the first step to staying on top of it.
Your Corporation Tax payment is due 9 months and 1 day after the end of your accounting period, which normally matches your company's financial year. So if your year end is 31 March, payment is due by 1 January the following year. Filing your Company Tax Return, the CT600, is due later, within 12 months of the end of the accounting period. That gap between the payment deadline and the filing deadline catches a lot of directors out, because HMRC expects the money before it expects the return.
The CT600 return needs to be filed online, along with a set of accounts and computations prepared to the correct tax rules, which are not always the same as the accounting rules used in your statutory accounts. Most companies file this alongside or shortly after submitting accounts to Companies House, since the underlying figures are closely related, though the two filings go to different places and follow different deadlines.
Payment needs to reach HMRC by the deadline, not just be sent by then, so leave enough time for the payment method you use to actually clear. Faster Payments usually lands the same or next working day, while Bacs can take up to 3 working days. Larger companies with profits over £1.5 million pay in quarterly instalments instead of one lump sum, so if your profits are growing towards that level, it is worth checking whether the instalment rules will apply to your next accounting period.
Late filing penalties start at £100 for being up to 3 months late, rising to £200 after that, with further tax geared penalties if you are more than 6 or 12 months late. Late payment triggers interest from the day after the due date, calculated daily, so even a short delay adds up. The most common cause of a missed deadline is not knowing the date in the first place, particularly after a change of year end or in a company's first year, when the accounting period can run for slightly more or less than 12 months.
Corporation Tax planning works best when it happens before your year end, not after. Reviewing profits a few months ahead gives you time to make decisions that genuinely affect the tax bill, such as timing capital purchases to use annual investment allowance, topping up pension contributions, or making sure directors' salaries and dividends are structured sensibly. Once the accounting period has closed, most of the significant planning options are gone and you are left simply reporting what happened.
None of this needs to be complicated. Most of the stress around Corporation Tax comes from finding out the numbers too late to do anything about them, not from the tax itself.
We keep your bookkeeping current, calculate your liability early, and file your CT600 well before the deadline, so there are no last minute surprises.
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