If you run a limited company in the UK, missing your Corporation Tax deadline does not just mean a penalty. HMRC charges interest from the day payment is late. Here is exactly when it is due and how to stay ahead of it.
The payment deadline
Your Corporation Tax is due 9 months and 1 day after your accounting period ends. If your year end is 31 March 2025, payment is due 1 January 2026.
The filing deadline is different. Your CT600 (the tax return itself) is not due until 12 months after your accounting period ends, three months later than the payment. Most business owners do not realise this. You owe the money before you have even filed the return.
Quick reference
| Year end | CT payment due | CT600 filing due |
|---|---|---|
| 31 March 2025 | 1 January 2026 | 31 March 2026 |
| 30 June 2025 | 1 April 2026 | 30 June 2026 |
| 31 December 2025 | 1 October 2026 | 31 December 2026 |
What happens if you miss it
⚠️ No grace period: HMRC charges interest at the official rate from the day after the deadline. The interest compounds, so a small shortfall left unpaid for months adds up faster than most people expect. Late filing of the CT600 carries separate penalties: £100 immediately, another £100 after three months, then tax-geared penalties from six months.
The harder problem: knowing what to pay
The deadline is easy to find. The harder part is knowing how much to set aside throughout the year, especially if your profit is still moving.
That is what Rooby does. It connects to your Xero data and shows your CT liability as it builds month by month, so by the time the deadline arrives, the money is already there.
💡 Got questions about your CT deadline? Your accountant should be your first call. If they are using Rooby, they will already have your live liability in front of them.
Rooby connects to Xero and tracks your Corporation Tax position month by month, so nothing comes as a surprise at payment time.