Corporation Tax does not have a single fixed payment date. When it is due depends on when your accounting period ends and how large your company's profits are. Getting these dates wrong means interest charges from HMRC from the day after the deadline, with no grace period and no reminder. Here is how the deadlines work.
The standard rule: 9 months and 1 day
For most limited companies, those with annual taxable profits below £1.5 million, Corporation Tax is due 9 months and 1 day after the end of the accounting period. This is calculated precisely: nine calendar months from the period end date, plus one day.
| Year end: 31 March | Payment due: 1 January (following year) |
| Year end: 30 April | Payment due: 1 February (following year) |
| Year end: 31 May | Payment due: 1 March (following year) |
| Year end: 30 June | Payment due: 1 April (following year) |
| Year end: 30 September | Payment due: 1 July (following year) |
| Year end: 31 December | Payment due: 1 October (following year) |
Note that the payment deadline and the CT600 filing deadline are different. You must pay by 9 months and 1 day. You must file the CT600 return by 12 months after the period end. You may have to pay before you have filed your return, based on your best estimate of the liability.
⚠️ Pay before you file: Most companies pay CT before the accounts are finalised and the CT600 is submitted. You pay based on the estimated liability, then adjust once the return is filed. If you overpay, HMRC repays the excess with interest. If you underpay, interest accrues from the original deadline date.
The CT600 filing deadline
The Corporation Tax return (CT600) must be filed with HMRC within 12 months of the end of the accounting period. This is a separate obligation from payment. You can be on time with payment and late with the return, or vice versa, both carry separate penalties.
| Obligation | Deadline |
|---|---|
| Pay Corporation Tax | 9 months and 1 day after period end |
| File CT600 return | 12 months after period end |
| File annual accounts with Companies House | 9 months after period end (private companies) |
Large companies: quarterly instalment payments
Companies with taxable profits above £1.5 million (divided by the number of associated companies) must pay Corporation Tax in quarterly instalments rather than as a single payment. This regime is called Quarterly Instalment Payments (QIPs).
The four payment dates for a standard 12-month accounting period are:
| Instalment | Due date | Amount |
|---|---|---|
| 1st | Month 7 of the accounting period | 25% of estimated full-year liability |
| 2nd | Month 10 of the accounting period | 25% of estimated full-year liability |
| 3rd | Month 13 (1 month after period end) | 25% of estimated full-year liability |
| 4th | Month 16 (4 months after period end) | Balance of actual liability |
Note that the first two instalments fall during the accounting period, before the profit is known. Companies must estimate their liability based on performance to date and adjust subsequent payments as the picture becomes clearer. HMRC charges interest on any shortfall between each instalment and what it should have been based on the eventual actual liability.
✓ Very large companies (profits above £20m): These companies pay earlier, instalments fall in months 3, 6, 9, and 12 of the accounting period. The entire liability is paid during the accounting period itself, before the year even ends.
Penalties for late payment and late filing
HMRC charges interest rather than fixed penalties for late CT payment. The late payment interest rate is HMRC's base rate plus 2.5%, currently 7.25% per annum (as at May 2026). Interest accrues from the day after the payment was due and is not tax deductible.
Late filing of the CT600 carries fixed penalties:
| How late | Penalty |
|---|---|
| 1 day late | £100 |
| 3 months late | Additional £100 |
| 6 months late | 10% of the unpaid CT (if any CT was outstanding) |
| 12 months late | Additional 10% of unpaid CT (20% if deliberate failure) |
The penalty for late payment is interest-based and therefore proportionate to how much is owed and how late it is. The penalty for late filing is fixed and applies even if there is no CT to pay, a company with a nil return that files late still receives the £100 penalty.
When the accounting period is not 12 months
A company's first accounting period often runs for less than 12 months (if incorporated mid-year) or, rarely, for up to 18 months if the period was extended. For periods shorter than 12 months, the deadlines are calculated from the actual period end, there is no proration. A 6-month period ending on 30 June still has a payment deadline of 1 April (9 months and 1 day from 30 June).
💡 Rooby tip: Rooby shows the upcoming CT payment date for each client based on their accounting period end, so you always know which bills are due next and can flag provisioning gaps early.
Rooby connects to Xero and shows upcoming Corporation Tax payment dates alongside live liability estimates for all your clients.