When Is Corporation Tax Due?
Free UK Deadline Guide 2025/26
One of the most common questions from UK limited company directors is: when is corporation tax due? The answer depends on your company’s accounting year end date — and getting it wrong means HMRC interest charges from day one. This guide explains exactly when corporation tax is due for every type of company, with a complete table of deadlines and a clear explanation of what happens if you miss them.
When Is Corporation Tax Due — Key Facts
Here are the essential facts about when corporation tax is due:
- When is corporation tax due (payment): 9 months and 1 day after your accounting period ends
- When is corporation tax due (filing): CT600 must be filed within 12 months of year end
- When is corporation tax due (large companies): Quarterly instalments apply above £1.5m profits
- When is corporation tax due (new companies): First payment due 9 months + 1 day after first year end
- When is corporation tax due (short periods): Same rule applies — 9 months + 1 day after the short period end
The full guide to when corporation tax is due — with worked examples for every common year end date — is below.
What this guide covers
The exact corporation tax payment deadline · CT600 filing deadline · A full table of deadlines by year end date · Large company quarterly instalment rules · What happens if you pay late · How to check when your corporation tax is due
The Corporation Tax Payment Deadline — The 9 Month + 1 Day Rule
The standard corporation tax payment deadline is 9 months and 1 day after the end of your company’s accounting period. This rule applies to all UK limited companies that are not classified as large (profits below £1.5 million per year).
| Accounting Year End | Corporation Tax Due | CT600 Filing Due |
|---|---|---|
| 31 January 2025 | 1 November 2025 | 31 January 2026 |
| 28 February 2025 | 1 December 2025 | 28 February 2026 |
| 31 March 2025 | 1 January 2026 | 31 March 2026 |
| 30 April 2025 | 1 February 2026 | 30 April 2026 |
| 31 May 2025 | 1 March 2026 | 31 May 2026 |
| 30 June 2025 | 1 April 2026 | 30 June 2026 |
| 31 July 2025 | 1 May 2026 | 31 July 2026 |
| 31 August 2025 | 1 June 2026 | 31 August 2026 |
| 30 September 2025 | 1 July 2026 | 30 September 2026 |
| 31 October 2025 | 1 August 2026 | 31 October 2026 |
| 30 November 2025 | 1 September 2026 | 30 November 2026 |
| 31 December 2025 | 1 October 2026 | 31 December 2026 |
✅ Most common year end: 31 March
Many UK limited companies use 31 March as their year end, aligned with the UK tax year. For these companies, corporation tax is due by 1 January — making it a January double deadline alongside self-assessment for director-shareholders.
The CT600 Filing Deadline — 12 Months After Year End
Separate from the payment deadline, your CT600 corporation tax return must be filed with HMRC within 12 months of your accounting period end. Note that the payment deadline (9 months + 1 day) comes before the filing deadline (12 months) — which means HMRC expects you to pay your corporation tax before you have filed the return that calculates it.
Your accountant will prepare and file your CT600 based on your statutory accounts. HMRC’s calculation of your liability is based on the figures in your CT600.
⚠ Late CT600 filing triggers immediate penalties
Filing your CT600 late results in an automatic £100 penalty — even if no corporation tax is owed and even if you have already paid. After 3 months late, a further £100 applies. After 6 months, 10% of unpaid tax is added. After 12 months, a further 10%.
Large Company Quarterly Instalment Payments
Companies with annual taxable profits above £1.5 million do not pay a single annual corporation tax payment. Instead, they pay in four quarterly instalments:
- Month 7 of the accounting period
- Month 10 of the accounting period
- Month 1 of the following accounting period
- Month 4 of the following accounting period
For most small and medium-sized UK limited companies, quarterly instalments do not apply. The single annual payment deadline is what matters.
When Is Corporation Tax Due for a New Company?
If your company was newly incorporated, your first accounting period runs from the date of incorporation to the end of your chosen accounting year — usually 12 months but sometimes shorter. Corporation tax for that first period is due 9 months and 1 day after that first year end, following exactly the same rule as established companies.
If your first accounting period is longer than 12 months (which can happen if incorporation falls mid-year), HMRC splits it into two corporation tax accounting periods and charges tax on each separately.
Calculate Your Corporation Tax Bill
Use our free corporation tax calculator to work out exactly how much is due before your payment deadline.
Calculate Corporation Tax → →What Happens If You Miss the Corporation Tax Deadline?
HMRC charges interest on late corporation tax payments from the day after the deadline. Interest is calculated at the Bank of England base rate plus 2.5%. Unlike VAT or PAYE, there are no fixed surcharge penalties for late payment of corporation tax — but interest compounds daily and can add up significantly over weeks or months.
If you cannot pay on time, contact HMRC’s Business Payment Support Service on 0300 200 3835 before the deadline to arrange a Time to Pay agreement. See our guide on how to pay corporation tax for full payment details including HMRC bank details and all accepted methods.
Final Thoughts
The answer to when is corporation tax due is the same for every UK limited company: 9 months and 1 day after your accounting year end. Mark this date in your calendar at the start of every accounting period — and use our free corporation tax calculator to estimate your bill well in advance so you can plan your cash flow accordingly.
For full details on payment methods and HMRC bank details, see our guide on how to pay corporation tax. All deadline information is sourced from HMRC’s official corporation tax deadlines guidance.