Corporation Tax Payment Deadline: 9 Months and 1 Day

For most small companies, the corporation tax payment deadline is 9 months and 1 day after the end of the accounting period. The Company Tax Return is due later, 12 months after the period ends, so the tax has to be paid before the return is technically due.

That gap catches many directors out. They see “12 months” for the return, assume the tax is due then too, and end up paying interest. This guide explains how the dates are worked out, gives examples for common year ends, and shows how to make sure the money is ready in time.

Key takeaways

• Small and medium companies pay corporation tax 9 months and 1 day after the period ends.
• The CT600 return is due 12 months after the period ends.
• Large companies pay by quarterly instalments instead.
• Interest runs on late payments from the due date.
• HMRC does not always send a bill, so diarise the date yourself.

What an accounting period is

An accounting period for corporation tax is the period your tax is calculated for. It usually matches your company's financial year, but it can never be longer than 12 months. If your first set of accounts covers more than 12 months, there are two accounting periods for tax, each with its own payment date and return. GOV.UK explains payment on its pay corporation tax page and the return on its Company Tax Returns page.

Deadlines for common year ends

The Companies House dates above assume a private company that is not filing its first accounts. First accounts, and changes to your year end, can shift these dates; our guide to company accounts deadlines explains how.

Why the tax is due before the return

Corporation tax is self-assessed. HMRC expects you to work out and pay what you owe by the payment date, whether or not the return has been filed. In practice, most small companies finalise their accounts and return before the payment date, so they pay the right amount. If that is not possible, pay an estimate by the deadline to limit interest, then settle any balance once the return is done.

How much you pay depends on your profits. Companies with profits between the lower and upper limits pay a rate adjusted by marginal relief; our marginal relief guide explains the calculation, and the current rates and limits are on GOV.UK.

When HMRC does not send a reminder

HMRC usually sends a notice to deliver a Company Tax Return and, for many companies, payment reminders. But it is the company's legal responsibility to pay on time whether or not a reminder arrives. New companies are a particular risk: if HMRC has not linked the company to its first accounting period correctly, the reminders may not be generated, yet the tax is still due on the normal date.

The safest approach is to treat your own year end as the trigger. The day your financial year ends, add the payment date and the filing date to your calendar, and check your company's HMRC online account a few weeks before the payment is due to confirm the payment reference and any amount already recorded. If the company has made a loss for the year, there may be no tax to pay, but a return is still required if HMRC has issued a notice to file.

Step by step: making sure you can pay on time

1. Diarise both dates the day your year ends: payment at 9 months and 1 day, return at 12 months.
2. Estimate the bill monthly from your management accounts during the year.
3. Set money aside in a separate savings account as profits are made.
4. Close the year promptly so the accounts and return can be prepared early.
5. Check the payment reference for the specific accounting period.
6. Pay a few working days early so the funds clear before the deadline.
7. If you cannot pay in full, contact HMRC before the deadline about a payment arrangement.

Worked example (illustrative example)

"Harbour Lane Joinery Ltd", an invented illustrative example, has a 31 December year end. Its accounts for the year to 31 December 2025 show a taxable profit, and the corporation tax bill is £9,000. The director assumed the tax was due with the return on 31 December 2026.

The accountant points out that payment was actually due by 1 October 2026. Because the company had been transferring £750 a month into a tax savings account during 2025, the money is there, and the director pays on 28 September using the reference for that accounting period. The return is filed in November, well before 31 December 2026. Had the director waited until December, interest would have run on the £9,000 for about three months. The company and figures are invented to show the timeline.

Common mistakes

• Assuming tax is due with the return rather than three months earlier.
• Using last year's payment reference for this year's bill.
• Forgetting long first periods create two accounting periods and two payment dates.
• Taking large dividends without leaving enough for the tax bill.
• Waiting for a reminder that may not arrive.

Get corporation tax done on time

Our corporation tax service starts from £250 per year, and our limited company packages start from £75 per month, including reminders of every payment and filing date. Before declaring dividends, read our guide to salary vs dividends so the tax money stays in the company.

Not sure when your company's tax is due? Get in touch or see our pricing.