Corporation Tax deadlines: filing, paying and penalties

Your company has two Corporation Tax deadlines, and the payment one comes first. You pay the tax 9 months and 1 day after the end of your accounting period, and file your Company Tax Return (CT600) within 12 months. Your accounts have their own deadline at Companies House.

Last checked against GOV.UK on 29 September 2026.

A4O Accounts prepares the CT600 from your books and files it with HMRC. See the CT600 software, or get started free.

Accounting period and financial year

Your Corporation Tax deadlines run from the end of your accounting period. That’s the period your Company Tax Return covers. It can’t be longer than 12 months, and it’s normally the same as the financial year your annual accounts cover.

The two can differ. The usual cases are your company’s first year, a year you lengthen or shorten, and a company that stops trading. You can check your accounting period dates in your business tax account with HMRC.

The key dates

Two things catch people out. The tax is due three months before the return, so you need to work out what you owe before you file. And you must still file a return if your company made a loss or has no tax to pay. If there’s nothing to pay, tell HMRC using its “nil to pay” form, or it will keep sending payment reminders.

A worked example

Your company’s year ends on 31 December 2025, and its accounting period is the same calendar year.

• 30 September 2026: accounts due at Companies House.
• 1 October 2026: Corporation Tax due to HMRC.
• 31 December 2026: Company Tax Return due to HMRC.

The accounts and the tax payment fall a day apart, so it’s simplest to finish the accounts and the tax computation together. See filing company accounts with Companies House for the accounts side.

If a deadline falls on a weekend or bank holiday, your payment needs to reach HMRC on the last working day before it, unless you pay by Faster Payments through online or telephone banking.

Large and very large companies

If your company’s profits are at an annual rate of more than £1.5 million, you normally pay by instalments instead of in one payment.

There are exceptions. A company doesn’t pay by instalments if its tax for the period is less than £10,000. A large company also doesn’t pay by instalments in the first period it goes over the £1.5 million threshold, as long as its profits are no more than £10 million. There’s no such grace period for very large companies. Both thresholds are divided by the number of associated companies, counting your own, so a small company in a group can still be large. The filing deadline stays at 12 months.

First years and long accounts

Your company’s first accounts usually cover more than 12 months. They start on the day the company was set up and end on the accounting reference date Companies House gives it. Because an accounting period can’t be longer than 12 months, you may need two returns to cover those accounts, each with its own payment deadline.

GOV.UK’s example: a company set up and trading from 11 May 2024, with a year end of 31 May 2025, files one return for 11 May 2024 to 10 May 2025 and another for 11 to 31 May 2025. Its payment deadlines are 11 February 2026 and 1 March 2026.

The same applies if you lengthen your company’s year. You must tell HMRC the new accounting period dates before the original filing date of your return, or you may get a late filing penalty. If your company didn’t start trading straight away, the rules differ. See how to file a CT600 and GOV.UK’s guide to first accounts.

Penalties for filing late

HMRC charges these if your Company Tax Return is late, whether or not you owe tax.

If your return is late three times in a row, the £200 penalties go up to £1,000 each. At 6 months late, HMRC’s estimate is called a “tax determination”. You can’t appeal against it. You still have to pay the tax and file the return, and HMRC then recalculates the interest and penalties. You can appeal a late filing penalty if you have a reasonable excuse, but only after you’ve filed the return.

Late accounts are penalised separately by Companies House. For a private company that’s £150 up to 1 month late, rising to £1,500 over 6 months, and doubled if your accounts are late two years in a row.

Paying late

HMRC charges interest on Corporation Tax paid after the deadline. The rate is linked to the Bank of England base rate. HMRC also pays interest if you pay early. Large companies are charged interest if their instalments turn out too low, and it’s worked out when the return is filed.

Filing in software

HMRC’s free online filing service closed on 31 March 2026, so your CT600 now goes through commercial software. Companies House accounts follow in April 2028.

A4O Accounts prepares the accounts and the CT600 from the same books, and files them with Companies House and HMRC. The dashboard and filings page show what’s due. See Corporation Tax software for how the tax is worked out. The help pages cover preparing and filing a CT600 and filing annual accounts.

More in this series: all the CT600 guides.