A corporation tax bill can feel as though it arrives before the year’s figures have properly settled. The key question – when is corporation tax due – has a simple general answer, but the date depends on your company’s accounting period rather than the date you happen to prepare the accounts.
For most UK limited companies, corporation tax must be paid nine months and one day after the end of the accounting period. Your Company Tax Return is due later, usually 12 months after the end of that period. Keeping those two deadlines separate is one of the easiest ways to avoid an expensive mistake.
When is corporation tax due for most companies?
If your company has a 31 March year end, its corporation tax payment deadline will normally be 1 January of the following year. The Company Tax Return for that same period is normally due by the following 31 March.
That gap can catch directors out. You may have up to a year to submit the return, but you do not have up to a year to pay the tax. HM Revenue & Customs (HMRC) expects payment based on a sensible calculation of the company’s taxable profit, even if the final return is still being completed.
For a company with a 31 December 2025 accounting period end, the main dates would be:
- Corporation tax payment due: 1 October 2026
- Company Tax Return due: 31 December 2026
This is why timely bookkeeping matters. If the records are incomplete until close to the payment deadline, there is less time to calculate the likely liability, check available reliefs and arrange payment with confidence.
Your accounting period determines the deadline
An accounting period for corporation tax usually follows the period covered by your statutory accounts. In many established companies this is 12 months, but it can be shorter, particularly in the first year of trading or when the company changes its year end.
Your first accounting period can be slightly more complicated. Companies House may show a first set of accounts covering more than 12 months, but an accounting period for corporation tax cannot exceed 12 months. HMRC will therefore split a longer period into two corporation tax accounting periods. Each period has its own tax calculation, payment date and Company Tax Return.
For example, if a new company’s first accounts cover 15 months, it may need to submit two tax returns: one for the first 12 months and one for the remaining three months. The deadlines will not necessarily be obvious from the Companies House accounts deadline alone, so it is worth checking the dates early.
A company that is not yet trading may be dormant for corporation tax purposes. Once it begins business activity – for example, selling services, buying stock, earning interest or employing staff – it may need to notify HMRC. New companies generally need to tell HMRC that they have started trading within three months. This helps ensure that HMRC has the right accounting period and can issue the relevant filing notices.
The payment date is not your accounts filing date
There are several compliance dates attached to a limited company, and they serve different purposes. Statutory accounts go to Companies House, the Company Tax Return goes to HMRC, and corporation tax is paid to HMRC. They can all have different deadlines.
Using the Companies House accounts filing deadline as a prompt for tax payment is risky. By then, the corporation tax payment date may already have passed. A clear annual timetable, based on your company year end, gives directors far more control.
When is corporation tax due for larger companies?
The nine-month-and-one-day rule applies to most small and medium-sized companies. Larger companies may have to pay corporation tax in instalments instead.
Broadly, a company can be treated as large where its taxable profits exceed £1.5 million, and very large where they exceed £20 million. These thresholds are reduced where there are associated companies, so groups and companies under common control can reach the instalment rules sooner than expected.
Large companies generally pay their tax in four instalments during the accounting period and shortly afterwards. Very large companies pay earlier still. The precise dates depend on the company’s circumstances, its taxable profits and whether it is in its first period above the relevant threshold.
This is an area where assumptions can be costly. A growing business that has made a one-off disposal, secured a major contract or increased profits sharply may move into the instalment regime without its directors realising. Forecasting taxable profit during the year, rather than waiting for year-end accounts, is particularly valuable in this position.
Paying before the tax return is finalised
It is perfectly normal to pay corporation tax before the Company Tax Return is submitted. The payment should be based on the best available estimate, supported by up-to-date bookkeeping and a review of tax adjustments.
Taxable profit is not always the same as the profit shown in your accounts. Some costs may not be deductible for corporation tax, while capital allowances, losses carried forward, pension contributions and qualifying reliefs can alter the final figure. This is one reason a quick glance at the bank balance is not a reliable way to estimate the bill.
If you pay too little, HMRC will charge late payment interest on the outstanding balance. If you pay too much, the overpayment can usually be repaid or set against another HMRC liability once the position is confirmed. Paying a prudent estimate by the deadline is often preferable to waiting for every last detail and missing the payment date.
What happens if you pay or file late?
Late payment and late filing are separate issues, and one does not cancel out the other.
If corporation tax is paid after the deadline, HMRC charges interest from the due date until the tax is paid. The interest rate can change, but the principle remains the same: delaying payment makes the liability larger. In some circumstances, HMRC may also charge penalties or take steps to recover the debt.
If the Company Tax Return is filed late, HMRC can charge an initial £100 penalty. A further £100 penalty can apply if it is still outstanding three months later. At six and 12 months late, further penalties may be based on 10% of the unpaid tax. Repeated late filing can also lead to higher fixed penalties.
The practical point is that you should deal with both dates. Filing the return on time does not remove interest on late tax, and paying the estimated tax does not remove a filing penalty if the return is delayed.
How to stay ahead of your corporation tax deadline
Corporation tax is easier to manage when it is treated as a regular cash-flow commitment rather than a year-end surprise. Monthly management information can show how profits are developing and help directors set money aside steadily. This is especially useful for businesses with seasonal income or uneven contract payments.
It also helps to keep business and personal spending separate, reconcile bank transactions regularly and retain records for all significant purchases. These habits reduce the rush at year end and make it easier to identify legitimate expenses and reliefs before the payment calculation is needed.
If cash flow is tight, do not ignore the deadline. It may be possible to discuss a Time to Pay arrangement with HMRC, but it is not automatic and should be approached before the debt becomes overdue. You will usually need a realistic proposal based on the company’s ability to pay. Interest may still apply, so early action is preferable.
At Coombs Chartered Accountants, we help directors build tax deadlines into their wider financial planning, using clear records and timely advice to avoid last-minute decisions.
A practical date to put in the diary
As soon as your accounting period ends, record two dates: the corporation tax payment deadline at nine months and one day, and the Company Tax Return deadline at 12 months. Then plan backwards. Allow time to complete the bookkeeping, review the accounts, calculate the tax and arrange payment before the deadline rather than on it.
That small piece of organisation gives you more than compliance. It gives you time to ask the right questions, protect cash flow and make decisions from accurate numbers rather than a looming HMRC date.
