When is corporation tax due? 2026/27 Payment & Penalty Guide

To manage cash flow and ensure strict compliance, advisors and companies must accurately determine when their tax liabilities mature. Under section 11 of the Finance Act 2026, the main rate of corporation tax remains at 25% for the financial year 2027.  The exact date you must pay this tax depends entirely on the size of the company’s taxable profits and the length of its accounting period.

To answer the core question—when is corporation tax due—HMRC enforces three distinct payment timelines based on whether a company is classified as small/medium, large, or very large.

Below is an exhaustive breakdown of the due dates, the impact of associated companies, the CT600 filing deadlines, and the doubled late filing penalties taking effect in 2026.

Small and Medium Companies: The General Rule

If a company’s taxable profits do not exceed £1.5 million, it falls under the standard corporation tax payment regime.

Under section 59D of the Taxes Management Act 1970 (TMA 1970), corporation tax for an accounting period is generally due and payable on the day following the expiry of nine months from the end of that period.  This is universally referred to as the “9 months and 1 day” rule.

If the accounting period ends on the last day of a calendar month, the due date strictly falls on the first day of the tenth month following.  For example, if a 12-month accounting period ends on 31 March, you must pay the corporation tax on 1 January of the following year.

Large Companies: The Quarterly Instalment Regime

HMRC accelerates the payment timeline for large companies. A company qualifies as “large” if its taxable profits for the accounting period exceed £1.5 million but do not exceed £20 million.

Large companies must pay their corporation tax in four quarterly instalments.  For a standard 12-month accounting period, you must meet the following deadlines:

• First instalment: Six months and 13 days after the start of the accounting period.
• Second instalment: Three months after the first instalment.
• Third instalment: Three months after the second instalment.
• Final instalment: Three months and 14 days after the end of the accounting period.

If you owe tax for an accounting period shorter than 12 months, HMRC alters the number of instalments, but the final instalment is invariably due three months and 14 days after the end of that short accounting period.

Very Large Companies: Accelerated Instalments

For the largest taxpayers, HMRC brings the payment dates forward by a further four months. A company is classified as “very large” in the first accounting period that its taxable profits exceed £20 million.

Very large companies must pay their four quarterly instalments concurrently with the accounting period generating the profits. For a 12-month accounting period, the payments fall due on the 14th day of months 3, 6, 9, and 12 of the accounting period.

“first instalment: two months and 13 days after the start of the accounting period… second instalment: three months after the first… third instalment: three months after the second… final instalment: three months after the third.”

The Impact of Associated Companies

You cannot assess a company’s profit threshold in isolation if it belongs to a broader corporate structure. When determining if a company is large (£1.5m threshold) or very large (£20m threshold), you must proportionately reduce the threshold limits by dividing them by the total number of associated companies.

For example, if a company has three associated companies (making four companies in total), the large company threshold drops from £1.5 million to £375,000, pulling much smaller entities into the quarterly instalment regime.  You must also proportionally reduce these thresholds if the accounting period is less than 12 months.

CT600 Filing Deadlines vs Payment Deadlines

Do not confuse the corporation tax payment deadline with the filing deadline.

While small and medium companies must pay their tax 9 months and 1 day after the accounting period ends, the statutory filing date for delivering the Company Tax Return (Form CT600) is generally 12 months after the end of the accounting period.  This creates a cash-flow quirk: you must accurately calculate and pay your tax liability three months before you are legally required to file the return detailing it.

Penalties for Late Filing and Late Payment (2026/27 Increases)

Failing to meet these deadlines triggers stringent financial penalties. The 2026/27 tax year introduces severe legislative increases to these penalty rates.

Doubled Late Filing Penalties (From 1 April 2026)

For returns where the statutory filing date falls on or after 1 April 2026, the government has significantly increased the fixed late filing penalties to restore their real-terms value against inflation.

• Initial late filing: The penalty increases from £100 to £200.
• Over 3 months late: The penalty increases from £200 to £400.
• Three successive failures: If a company repeatedly files late, these escalated penalties now rise to £1,000 (initial) and £2,000 (over 3 months late).

Tax-Related Penalties for Prolonged Delays

If the company fails to deliver its return for more than 6 months past the filing date, HMRC imposes a tax-related penalty. You must pay an additional 10% of the unpaid tax calculated at the date the penalty is incurred.

“Unpaid tax at 2 May 2021 (day following the day penalty incurred) £20,000. Tax related penalty £20,000 x 10% = £2,000”

If the return remains outstanding 12 months after the filing date, this tax-related penalty doubles to 20% of the unpaid tax.

Summary Table: Corporation Tax Deadlines and Penalties

Next steps for research: Audit all corporate groups to verify the exact number of associated companies under the current rules, to ensure no entities have inadvertently breached the proportionately reduced £1.5 million limit and unknowingly triggered the quarterly instalment regime.