When Is Corporation Tax Due in the UK?

The payment deadline

For most small UK companies, Corporation Tax is due 9 months and 1 day after the end of the Corporation Tax accounting period. For example, a period ending on 31 March 2027 normally has a payment deadline of 1 January 2028.

This is the tax payment date. Late payment can attract interest even where the Company Tax Return has not yet reached its filing deadline. Large and very large companies can have different instalment rules.

The Company Tax Return deadline

The Company Tax Return, commonly called the CT600, is normally due 12 months after the accounting period ends. Using the same 31 March 2027 example, the return would normally be due on 31 March 2028.

The important point is that payment normally comes before the CT600 deadline. Directors who wait until month twelve to prepare the tax calculation can already be late with the payment.

Companies House accounts are separate

Annual accounts filed at Companies House have their own deadline. They support the tax work, but filing accounts does not file the CT600 or pay Corporation Tax. Record all three events separately: Companies House accounts, Corporation Tax payment and Company Tax Return.

Accounting period and company year end

A Corporation Tax accounting period often matches the company’s financial year, but not always. First Companies House accounts can cover more than 12 months, while a Corporation Tax accounting period cannot normally exceed 12 months. A new company may therefore need more than one CT600 for its first set of accounts.

Practical example

If the company cannot pay

Do not ignore a cash-flow problem. HMRC may charge interest and take collection action. Contact HMRC or seek advice early; a Time to Pay arrangement may be considered depending on the company’s position, but it is not automatic.

Common deadline mistakes

• Confusing the payment date with the CT600 filing date.
• Assuming Companies House accounts complete the HMRC filing.
• Using the company year end without checking the Corporation Tax accounting period.
• Spending cash that should have been reserved for tax.
• Leaving company records and the tax estimate until month twelve.

Build the deadline into the year

1. Confirm each accounting period end date.
2. Add 9 months and 1 day for the usual payment deadline.
3. Add 12 months for the usual CT600 deadline.
4. Check the Companies House accounts deadline separately.
5. Update company records and tax estimates during the year.
6. Ask for help early if the company cannot pay.