Do You Pay Corporation Tax Before Filing a CT600?
In the UK, Corporation Tax is due nine months and one day after your accounting period ends, while the CT600 return is due within twelve months. Discover how to balance these dual deadlines.
Yes, Corporation Tax payment is due before the CT600 filing deadline. You must pay your tax liability nine months and one day after your accounting period ends, whereas you have a full twelve months to file your Company Tax Return. This timeline requires you to calculate your tax liabilities well before you are legally required to submit your return.
Key Takeaways: Corporation Tax payment vs filing timelines
The statutory timelines for fulfilling your corporate tax obligations diverge significantly, meaning payment must always take priority over filing. Below is a comparison table outlining the standard deadlines for British companies.
| Tax Obligation | Standard Statutory Deadline |
|---|---|
| Corporation Tax Payment | 9 months and 1 day after the end of your accounting period |
| Company Tax Return (CT600) Filing | 12 months after the end of your accounting period |
Are Corporation Tax payment and filing deadlines different?
Yes, the payment deadline falls approximately three months before the filing deadline, which often catches new UK business owners off-guard.
This dual-deadline framework means that you cannot wait for the final CT600 filing cut-off date to determine your tax liability. Companies must calculate their taxable profits early to avoid late payment interest charges from HM Revenue and Customs.
When is the Corporation Tax payment deadline?
The statutory deadline to pay Corporation Tax is exactly nine months and one day after your active accounting period closes.
According to Section 59D of the Taxes Management Act 1970, this timeline is fixed for companies that are not classified as large. To calculate your payment due date, you must follow these sequential steps:
- Identify the exact end date of your company's Corporation Tax accounting period.
- Add nine calendar months to that ending date.
- Add one additional day to determine the final deadline for funds to clear with HMRC.
For example, if a company's accounting period ends on 31 March 2026, adding nine months leads to 31 December 2026. Adding one extra day establishes the final payment deadline as 1 January 2027.
When is the CT600 Corporate Tax Return filing deadline?
The Company Tax Return (CT600) must be filed within twelve months of the end of your accounting period.
Under Schedule 18 of the Finance Act 1998, companies have a full year to submit their formal returns. If your accounting period ends on 31 March 2026, your CT600 filing deadline is 31 March 2027.
Although you have twelve months to file, you must accurately determine your tax liability months earlier to meet the payment deadline. Filing the CT600 early is highly recommended to ensure your payment matches your final return exactly.
Do different rules apply to large companies with high profits?
Yes, large companies with augmented profits exceeding 1.5 million pounds do not follow the standard nine-month payment rule.
Under Section 59E of the Taxes Management Act 1970, large and very large companies must navigate a separate regime. Instead of a single year-end payment, these entities must pay their liabilities in quarterly instalments.
| Company Profit Category | Augmented Profit Threshold | Payment Scheme | Statutory Reference |
|---|---|---|---|
| Standard (Small/Medium) | Up to £1.5 million | Single payment 9 months and 1 day after period ends | s.59D TMA 1970 |
| Large | Over £1.5 million up to £20 million | Quarterly instalment payments (QIPs) starting in month 7 | s.59E TMA 1970 |
| Very Large | Over £20 million | Accelerated quarterly instalment payments starting in month 3 | s.59E TMA 1970 |
How does the April 2026 HMRC filing service change affect you?
Starting 1 April 2026, HMRC is closing its free online tax filing service, making commercial software mandatory for submissions.
Official HMRC guidance confirms that companies can no longer use the free HMRC portal to file accounts and CT600 returns after this date. Business owners must purchase and implement third-party commercial software that is compatible with HMRC systems.
Paper filing will remain prohibited for the vast majority of UK corporate taxpayers. HMRC will only permit exceptions under highly restricted circumstances, such as when filing a return entirely in the Welsh language.
Can I file my CT600 return after I pay my Corporation Tax?
Yes. Since the payment deadline is nine months and one day after the period ends, and the filing deadline is twelve months, it is standard practice to pay HMRC first and file the CT600 later.
What happens if I calculate my Corporation Tax incorrectly because I paid before filing?
If you pay too little, HMRC will charge interest on the outstanding balance from the payment deadline. If you overpay, you can claim a refund or offset the credit against future liabilities when you file the final CT600.
Are there penalties if I pay my Corporation Tax on time but file the CT600 late?
Yes. Even if your tax is paid in full, HMRC will issue automatic late-filing flat penalties starting at £100 if the CT600 is not submitted within the twelve-month statutory limit.
Do the payment deadlines change if my accounting period is shorter than 12 months?
No. The deadline to pay remains nine months and one day after the end of your short accounting period, meaning your payment date simply shifts forward to align with that specific end date.