Key facts
- The standard deadline is 9 months and 1 day after the end of the accounting period.
- Large companies (profits over £1.5 million) must pay in quarterly instalments during the period.
- The payment deadline is separate from the filing deadline (12 months after the period end).
- Interest runs automatically from the day after the due date — no grace period.
The Standard Deadline
For most companies, Corporation Tax must be paid within 9 months and 1 day after the end of the accounting period to which the liability relates.[1]
This means:
- If your accounting period ends on 31 March 2026, the deadline is 1 January 2027
- If your accounting period ends on 31 December 2025, the deadline is 1 October 2026
- If your accounting period ends on 30 June 2026, the deadline is 1 April 2027
There is no grace period. If payment is even one day late, HMRC charges interest from the day after the original due date.[1]
Common Year-End Dates & Deadlines
The table below shows payment and filing deadlines for the most common accounting period end dates:[1][4]
| Period End | CT Payment Due | CT600 Filing Due | Accounts to Companies House |
|---|---|---|---|
| 31 March 2025 | 1 January 2026 | 31 March 2026 | 31 December 2025 |
| 30 June 2025 | 1 April 2026 | 30 June 2026 | 31 March 2026 |
| 30 September 2025 | 1 July 2026 | 30 September 2026 | 30 June 2026 |
| 31 December 2025 | 1 October 2026 | 31 December 2026 | 30 September 2026 |
| 31 March 2026 | 1 January 2027 | 31 March 2027 | 31 December 2026 |
Filing vs payment: The CT600 return must be filed within 12 months of the period end, but the tax itself must be paid within 9 months and 1 day. Many companies file their return after paying — that’s perfectly fine, provided the payment amount is correct.[4] When you’re ready, you can file the return online with HMRC-recognised software.
Short Accounting Periods
If a company’s accounting period is shorter than 12 months (for example, the first period after incorporation), the same rule applies: the tax is due 9 months and 1 day after the end of that shorter period.[1]
If the period is longer than 12 months, HMRC splits it into two separate accounting periods (maximum 12 months each), and each has its own payment deadline.
Large Companies — Quarterly Instalments
Companies whose taxable profits exceed £1.5 million (divided by the number of associated companies) do not wait until 9 months and 1 day. Instead, they must pay in quarterly instalments during the accounting period itself.[3]
For a 12-month period, instalments are due in months 7, 10, 13, and 16 from the start of the period. For very large companies (profits over £20 million), instalments fall in months 3, 6, 9, and 12.
Tip: If you expect your profits to cross the £1.5 million threshold, review your instalment obligations early. Getting it wrong can lead to interest charges on underpaid instalments.
What Happens If You Miss the Deadline?
There is no separate penalty for paying Corporation Tax late (unlike late filing, which carries its own penalties). However, HMRC charges late payment interest from the day after the due date until payment is received.[1]
The interest rate is set by HMRC and is linked to the Bank of England base rate. It is not tax-deductible.
If the company’s return is also filed late, separate filing penalties apply — see Interest & Penalties.
Frequently Asked Questions
When must I pay Corporation Tax?
Corporation Tax must be paid within 9 months and 1 day after the end of the accounting period. There is no grace period — HMRC charges interest from the day after the due date if payment is late.
Do I need to pay Corporation Tax before filing my CT600?
Yes. The payment deadline (9 months and 1 day) falls before the CT600 filing deadline (12 months). You should estimate and pay your tax liability, then file the formal return afterwards.
When do large companies pay Corporation Tax?
Companies with profits over £1.5 million (divided by associated companies) must pay in quarterly instalments during the accounting period itself, in months 7, 10, 13, and 16 from the start of the period.
Is there a penalty for paying Corporation Tax late?
There is no separate penalty for late payment, but HMRC charges late payment interest automatically from the day after the due date until payment is received. The interest is not tax-deductible.
Further Reading
- Paying Corporation Tax — payment methods and HMRC bank details
- Quarterly Instalment Payments — the rules for large and very large companies
- Interest & Penalties — late filing penalties and interest rates
- Key Corporation Tax Dates — a full timeline of dates mapped to your accounting period
- Filing Deadlines — when the CT600 return must be submitted
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Sources
- Pay your Corporation Tax bill: deadlines — GOV.UK
- Pay your Corporation Tax bill — GOV.UK
- Corporation Tax: quarterly instalment payments — GOV.UK
- Company Tax Returns: deadlines — GOV.UK