Corporation Tax deadlines and CT600 due date

CT600 deadline and Corporation Tax due date: the short answer

The CT600 filing deadline is 12 months after the end of your accounting period. The Corporation Tax payment deadline is earlier: 9 months and 1 day after the end of the accounting period. For a year ending 31 March 2026, the tax is due on 1 January 2027 and the CT600 on 31 March 2027.

These two dates are different, and the payment date comes first. That catches many new directors out.

Corporation Tax deadlines at a glance: the four key dates

Source: GOV.UK, accounts and tax returns for private limited companies, paying Corporation Tax, and running a limited company. Your accounting period for Corporation Tax is normally the same 12 months as your company financial year.

1. Companies House annual accounts

File annual accounts with Companies House within 9 months of the end of your company's financial year. For your first set of accounts, the deadline is 21 months from the date you registered the company (because the first period can be longer).

Late filing triggers automatic Companies House penalties starting at £150 and rising sharply.

2. Corporation Tax payment: when is Corporation Tax due?

Pay Corporation Tax to HMRC 9 months and 1 day after the end of your accounting period. So for a year ending 31 March, payment is due by 1 January.

Companies with taxable profits above £1.5m pay in instalments, and companies with profits above £20m pay earlier still. The limits are divided by the number of associated companies plus one. See the instalments section below.

3. CT600 company tax return: when is the CT600 due?

File the CT600 with HMRC within 12 months of the end of your accounting period. So if your year ends 31 March 2026, the CT600 is due by 31 March 2027.

Payment is due before the return: 9 months and 1 day vs. 12 months for filing. Most companies finish the accounts and the CT600 before the payment date, so they know exactly what they owe. If you file late and guess the payment, you risk paying too little and being charged interest on the shortfall.

You must file a CT600 even if you made a loss or owe no tax, once HMRC has sent you a notice to deliver a Company Tax Return. If no tax is due, you tell HMRC that no payment is due. If the company's accounts cover more than 12 months (common in the first year), HMRC splits it into two Corporation Tax accounting periods, requiring two CT600s. Each has its own payment date, 9 months and 1 day after each period ends; both returns are due 12 months after the end of the period of account.

4. Confirmation statement

File a confirmation statement at Companies House at least once every 12 months. The 14-day filing window starts from your statement date. Failing to file is a criminal offence and can lead to the company being struck off.

Corporation Tax due dates by year end

Payment is due 9 months and 1 day after your year end; the CT600 return is due 12 months after it. The Companies House accounts date is shown too, because it falls between the two.

What if the deadline falls on a weekend or bank holiday?

The deadline does not move. GOV.UK says your payment must reach HMRC on the last working day before it, unless you pay by Faster Payments. For a year ending 31 March 2026 the payment date is 1 January 2027, a bank holiday, so pay by Thursday 31 December 2026 unless you use Faster Payments.

Leave time for the payment method you choose to clear. GOV.UK gives same day or next day for Faster Payments, CHAPS and card payments, 3 working days for Bacs or a Direct Debit you have used with HMRC before, and 5 working days for a first Direct Debit. Online CT600 filing works at weekends.

Large companies: Corporation Tax is paid in instalments

If your taxable profits are above £1.5 million, you normally pay in quarterly instalments instead of one payment. A company is not required to pay by instalments if its total tax liability for the period is under £10,000, and there are other exceptions for companies with profits of no more than £10 million. The £1.5 million limit is divided by the number of associated companies plus one.

For a 12-month period, the four instalments fall 6 months and 13 days after the period starts, then every 3 months. GOV.UK gives this example for a year from 1 January 2026 to 31 December 2026:

• 14 July 2026
• 14 October 2026
• 14 January 2027
• 14 April 2027

Companies with profits over £20 million follow separate rules. See the GOV.UK guidance on paying Corporation Tax in instalments.

First year deadlines for a new company

A new company has 21 months from its registration date to file its first accounts at Companies House. Your first Corporation Tax accounting period starts when the company starts trading or has income, which can differ from the incorporation date, and a long first year can create two accounting periods. Each has its own CT600 and payment date. Check both before you diary the dates.

Is the Corporation Tax deadline the same as the Companies House deadline?

No: they are separate. Companies House accounts are due 9 months after the year end (21 months from incorporation for the first accounts); HMRC payment is 9 months and 1 day; the CT600 is 12 months. Filing accounts with Companies House does not file the CT600.

Penalties for missing each deadline

More detail: Corporation Tax late payment interest, CT600 late filing penalties and the Corporation Tax penalties overview.

Common mistakes

• Diarising 12 months for everything and paying the tax three months late.
• Assuming no tax means no return. A CT600 is still required.
• Paying on the deadline by a method that takes 3 to 5 working days.
• Using the wrong 17-character payment reference, so the payment is applied to the wrong bill.
• Forgetting the confirmation statement, which runs on a separate cycle from the year end.

Stay on top

• Diary all four dates as soon as your accounting period is fixed
• File accounts early to give yourself buffer for revisions
• Set up reminders 60, 30, and 7 days before each deadline
• If you can't make a deadline, contact HMRC or Companies House before the deadline: appeals are easier than after-the-fact

For the full guide to the return itself, read the CT600 guide or see our Corporation Tax service.