Tools and templates

CT600 filing deadline and payment date calculator

Enter the company's accounts period to see when each Corporation Tax return (CT600) is due and when the tax must be paid. A return is normally due 12 months after the accounting period ends and the tax 9 months and 1 day after it. A period of account longer than 12 months is split into two accounting periods.

Last reviewed 28 October 2026

Key facts

CT600 filing date	12 months after the accounting period ends, or later in the cases below (Finance Act 1998, Schedule 18, para 14)
Period of account up to 18 months	Every return for it is due 12 months after the period of account ends
Period of account over 18 months	Due 30 months after the period of account starts, if that is later
Notice to file served late	3 months after the notice, if that is later
Payment, profits up to £1.5 million	9 months and 1 day after the accounting period ends
Large companies (over £1.5 million)	4 quarterly instalments, from 6 months and 13 days after the period starts
Very large companies (over £20 million)	4 instalments, from 2 months and 13 days after the period starts
Late filing penalty	£200, then £400, for returns due from 1 April 2026 (was £100 and £200)

As at 25 October 2026.

Work out the dates

Enter the period of account and select Work out the dates.

Worked examples

Accounts period	Accounting periods	CT600 due	Tax payable
1 April 2026 to 31 March 2027	One	31 March 2028	1 January 2028
1 January to 31 December 2026	One	31 December 2027	1 October 2027
1 January 2025 to 31 March 2026 (15 months)	1 January to 31 December 2025, and 1 January to 31 March 2026	Both 31 March 2027	1 October 2026 and 1 January 2027

A large company with an accounting period from 1 April 2026 to 31 March 2027 pays its instalments on 14 October 2026, 14 January 2027, 14 April 2027 and 14 July 2027. A very large company with the same period pays on 14 June 2026, 14 September 2026, 14 December 2026 and 14 March 2027.

How the dates are worked out

Accounting periods. A Corporation Tax accounting period is never longer than 12 months. A longer period of account is split into the first 12 months and the remainder; profits are divided between them by days, capital allowances are worked out for each, and each gets its own CT600 with the same accounts attached.
Filing date. The latest of 12 months after the accounting period ends; 12 months after the period of account ends (if it is not longer than 18 months) or 30 months after it starts (if it is); and 3 months after HMRC served the notice to file.
Payment. For profits of up to £1.5 million at an annual rate, divided by 1 + the number of associated companies, the tax is due 9 months and 1 day after the accounting period ends. If that is a weekend or bank holiday, the money must reach HMRC by the last working day before, unless you pay by Faster Payments.
Instalments. Above that threshold the company pays in quarterly instalments, unless its tax is under £10,000 or it is in its first year of being large with profits of no more than £10 million (also divided by 1 + associated companies) and was not large in the previous 12 months. Short periods are tested at an annual rate.

Filing a CT600 now

HMRC closed its free online Company Tax Return service, and the joint Companies House and HMRC filing service, on 31 March 2026. Returns are now filed with commercial software, by the company or its agent; paper is allowed only with a reasonable excuse or for a return in Welsh. HMRC does not intend to introduce Making Tax Digital for Corporation Tax.

If the company changes its accounting period dates, tell HMRC before the original filing date, or a late filing penalty may arise.

Assumptions and limits

Months are counted to the corresponding date, and from a month end to a month end, as for Companies House deadlines. For periods that end on the 29th, 30th or 31st, compare the result with the dates in the company's HMRC online account.
The very large company threshold of £20 million is reduced for companies in a group; the calculator does not apply that reduction.
It shows dates, not amounts of instalments, and it does not include interest on late payment.
Figures as at 25 October 2026, before the Autumn Budget on 28 October 2026.

Frequently asked questions

When is my CT600 due?

Normally 12 months after the end of the accounting period it covers. For a period of account longer than 12 months, both returns are due 12 months after the period of account ends, if it is no longer than 18 months.

When do I pay Corporation Tax?

For most companies, 9 months and 1 day after the end of the accounting period, so 1 January 2028 for a year ending 31 March 2027. Large companies pay in quarterly instalments.

Is the tax due before the return?

Usually, yes. The payment date is 9 months and 1 day after the period ends, three months before the return is normally due.

What are the penalties for a late CT600 now?

For a return due on or after 1 April 2026: £200 if up to 3 months late and £400 in total after that, rising to £1,000 and £2,000 for a third late return in a row.

Can I still file a CT600 on HMRC's website?

No. HMRC's free filing service closed on 31 March 2026. Returns are now filed with commercial software, by the company or its agent.

Sources

Prepare your statutory accounts

Create an account and set up your company from the Companies House register; your first set of accounts is free. The trial balance import and the CT600 are in preparation.

Join the waitlist

General information about UK company law and tax, not legal or tax advice. The directors remain responsible for the accounts and returns they approve and file.