For most UK companies, Corporation Tax is due 9 months and 1 day after the end of the company’s accounting period. However, companies with larger taxable profits may have to pay Corporation Tax in quarterly instalments, while very large companies have even earlier payment dates. The important point is that your Corporation Tax payment deadline is not necessarily the same as your Company Tax Return filing deadline. A company can therefore have one date for paying its tax and another for submitting its return to HMRC.

This guide explains how the deadlines work, how to calculate your payment date, what changes for new companies and larger businesses, and what happens if you pay late.

What Is Corporation Tax?

Corporation Tax is a tax charged by HM Revenue & Customs (HMRC) on the taxable profits of companies and certain other organisations. A limited company may have to pay Corporation Tax on profits from activities such as:

• Trading income
• Certain investment income
• Chargeable gains
• Other taxable profits

The amount of Corporation Tax you owe is determined by your taxable profits and the applicable tax rules for the accounting period. Your company's accounting period for Corporation Tax is the period covered by its Company Tax Return. It cannot normally exceed 12 months, although a newly incorporated company can have more than one Corporation Tax accounting period during its first financial year. This distinction matters because your Corporation Tax deadline is calculated from the end of the relevant accounting period, not simply from the anniversary of incorporation.

When Is Corporation Tax Due?

For companies with taxable profits of £1.5 million or less, Corporation Tax is normally due:

9 months and 1 day after the end of the accounting period.

This is the standard rule for most small and medium-sized UK companies.

Example: 31 March year-end

Suppose your company's accounting period ends on 31 March 2026. The Corporation Tax payment deadline is: 1 January 2027, The calculation is nine months and one day after 31 March.

Another example

If your accounting period ends on 30 June 2026, your Corporation Tax is generally due on: 1 April 2027, The exact date should always be checked against your company's HMRC accounting period rather than estimated from your incorporation date. HMRC allows companies to check their accounting period through their business tax account.

Corporation Tax Payment Deadline vs Company Tax Return Deadline

One of the most common mistakes made by company directors is treating these two deadlines as identical. They are not. For a typical company:

The tax payment therefore usually comes before the Company Tax Return deadline. For example, if your accounting period ends on 31 March 2026, you may need to pay Corporation Tax by 1 January 2027 even though the Company Tax Return can generally be submitted later. That means waiting until the tax return deadline to think about payment can leave a company unexpectedly short of cash.

How to Calculate Your Corporation Tax Due Date

The simplest approach is to start with the end date of your Corporation Tax accounting period.

Step 1: Find your accounting period end date

Your accounting period may correspond with your company's financial year, but this is not always the case. New companies in particular can have unusual first-year dates because their first accounting period can be different from subsequent periods.

Step 2: Add nine months

Take the final day of the accounting period and move forward nine months.

Step 3: Add one day

Your normal Corporation Tax payment deadline is one day after those nine months.

Step 4: Check HMRC

Do not rely solely on a calendar calculation where the company has unusual accounting periods, group structures or significant taxable profits. HMRC's guidance confirms that the accounting period affects both the payment deadline and Company Tax Return deadline.

What About New Companies?

New companies can find Corporation Tax deadlines particularly confusing. When a company is incorporated, its first Corporation Tax accounting period does not necessarily match its first set of Companies House accounts. HMRC establishes the company's Corporation Tax accounting period after it has been registered for Corporation Tax. The company receives information from HMRC showing the relevant dates, and directors should check these carefully.

A newly incorporated company can also have two Corporation Tax accounting periods covering its first set of accounts. This can happen because a Corporation Tax accounting period cannot exceed 12 months.

Why this matters

Imagine a company has a relatively long first financial period. Its Companies House accounts may cover more than 12 months, but HMRC may divide the period into separate Corporation Tax accounting periods. That can result in different tax return and payment calculations. For a startup, this is one reason it is worth establishing the company's HMRC deadlines early rather than assuming everything follows the Companies House filing calendar.

When Do Large Companies Pay Corporation Tax?

The standard 9-month-and-one-day rule does not apply to all companies. Companies with taxable profits above £1.5 million may generally have to pay Corporation Tax through quarterly instalments. There are specific exceptions and special rules, including rules concerning groups of companies. For a 12-month accounting period, a large company normally makes four instalment payments. The standard instalment dates are:

• 6 months and 13 days after the start of the accounting period
• 3 months after the first instalment
• 3 months after the second instalment
• 3 months and 14 days after the end of the accounting period.

Example of quarterly instalments

Suppose a company has an accounting period from 1 January 2026 to 31 December 2026. Its normal instalment dates would be:

The company therefore begins paying Corporation Tax before its accounting period has ended. This is a major cash-flow difference compared with the standard small-company arrangement.

What If Your Company Has Profits Above £20 Million?

Very large companies have an even earlier Corporation Tax payment regime. For companies with annual taxable profits above £20 million, subject to the rules concerning groups and accounting periods, quarterly instalments are generally brought forward.

For a 12-month accounting period, payments are normally due on the 14th day of months 3, 6, 9 and 12 of the accounting period. For example, a company with a 1 January to 31 December accounting period would normally have instalment dates of:

• 14 March
• 14 June
• 14 September
• 14 December

These rules are primarily relevant to larger businesses, but they become important for fast-growing companies that move rapidly from startup to substantial profitability.

What Happens If You Pay Corporation Tax Late?

Missing the Corporation Tax payment deadline can result in interest being charged by HMRC. HMRC's guidance confirms that interest on late Corporation Tax runs from the normal payment due date. This is separate from penalties that may arise from failing to submit the Company Tax Return on time. In other words, there are potentially two different problems:

1. You paid the tax late.
2. You filed the tax return late.

They should not be treated as the same thing. Even if your company has already paid its Corporation Tax, submitting the Company Tax Return late can still result in a filing penalty. HMRC specifically notes that late filing penalties can apply even where there is no Corporation Tax to pay.

What If You Cannot Afford the Corporation Tax Bill?

This is where cash-flow planning becomes critical. A company should not wait until the payment deadline to discover that it cannot afford its tax bill. Corporation Tax is generally calculated on taxable profit, not simply on the amount of cash sitting in the business bank account. That distinction can catch founders off guard.

Example

A consultancy makes £100,000 of sales and records significant taxable profit. However, it has also spent heavily on equipment, paid suppliers and withdrawn money from the business. The bank balance may look modest even though the company has generated a substantial taxable profit.

The result can be an uncomfortable Corporation Tax bill. For this reason, businesses should consider setting aside money for Corporation Tax throughout the year rather than treating the tax bill as an end-of-year surprise. If a company is struggling to pay, it should deal with HMRC promptly rather than simply ignoring the deadline.

Do You Need to Wait for HMRC to Tell You to Pay?

No. Corporation Tax operates under a self-assessment system. The company's obligation to calculate and pay its tax does not depend on HMRC sending a demand for the payment. This is an important distinction for directors. Not receiving a reminder does not normally mean that the payment deadline has disappeared. The company remains responsible for determining what it owes and paying it on time.

How Should a Company Plan for Its Corporation Tax Deadline?

A simple tax calendar can prevent many avoidable problems.

1. Record the accounting period end date

Make sure the director, accountant and whoever handles bookkeeping are all working from the same date.

2. Put the payment date in the company calendar

Do this well before the deadline.

3. Estimate taxable profit throughout the year

Do not wait until accounts are completed before thinking about Corporation Tax.

4. Create a tax reserve

Many businesses transfer a portion of available cash into a separate account or reserve so that tax money is not accidentally spent.

5. Review the estimate before payment

If profits have increased substantially, the original Corporation Tax estimate may be too low.

6. Confirm the payment reference

Using the correct HMRC payment reference helps ensure the payment is allocated to the correct accounting period.

7. Allow time for electronic payments

Do not leave payment until the final few hours. The practical arrival time can depend on the payment method and banking arrangements.

A Common Mistake: Confusing Companies House With HMRC

Companies House and HMRC have different responsibilities. Companies House maintains the public register of UK companies and receives documents such as annual accounts and confirmation statements. HMRC administers Corporation Tax and other taxes.

A company may therefore have obligations to both organisations at different times. For founders managing a UK company remotely, this distinction is particularly important. Using Companies House as the only source of compliance information can result in an overlooked HMRC obligation.

IncorpUK, as a UK company formation and management platform for global founders, sits within this wider compliance landscape, but directors still need to understand which obligations belong to Companies House and which belong to HMRC.

Corporation Tax Deadline Checklist

Before your company's payment date, check:

• What is the company's Corporation Tax accounting period?
• When does that period end?
• Is the company subject to the standard 9-month-and-one-day rule?
• Are taxable profits above the quarterly instalment threshold?
• Is the company part of a group that affects the threshold?
• Has the Corporation Tax liability been estimated?
• Is enough cash available to make the payment?
• Is the correct HMRC payment reference being used?
• Has the Company Tax Return deadline also been recorded?
• Has the payment been scheduled early enough?

For most smaller companies, this checklist is enough to prevent the most common deadline errors.

Frequently Asked Questions

When is Corporation Tax due for a small UK company?

For companies with taxable profits of £1.5 million or less, Corporation Tax is normally due 9 months and 1 day after the end of the accounting period.

Is Corporation Tax due before the tax return?

Usually, yes. The payment deadline for a typical company is 9 months and 1 day after the accounting period ends, while the Company Tax Return is generally due 12 months after the end of the accounting period.

Is Corporation Tax due on the same date every year?

Not necessarily. The payment date depends on the company's accounting period. If the accounting period changes, the Corporation Tax deadline can change too.

When do large companies pay Corporation Tax?

Companies with taxable profits above £1.5 million may normally have to pay Corporation Tax through quarterly instalments. Special rules apply to very large companies with taxable profits above £20 million.

What happens if Corporation Tax is paid late?

HMRC can charge interest on late Corporation Tax payments. The interest generally runs from the normal payment due date.

Does Companies House tell me when my Corporation Tax is due?

No. Companies House and HMRC have separate responsibilities. Corporation Tax deadlines are administered by HMRC.

Can a new company have more than one Corporation Tax accounting period?

Yes. A company's Corporation Tax accounting period cannot exceed 12 months, so a newly incorporated company can have two Corporation Tax accounting periods within its first set of accounts.

Do I have to pay Corporation Tax if my company made no profit?

Generally, Corporation Tax is charged on taxable profits. If a company has no taxable profits, it may have no Corporation Tax to pay, although it can still have reporting and filing obligations.

Can I pay Corporation Tax early?

Yes. Companies can make payments before the normal due date. HMRC's rules also provide for interest in certain circumstances where tax has been paid early.

Conclusion: Know Your Corporation Tax Date Before You Need It

For most UK companies, the key rule is straightforward: Corporation Tax is normally due 9 months and 1 day after the end of the accounting period. But that simple rule has important exceptions. New companies can have multiple Corporation Tax accounting periods, companies with profits above £1.5 million may move to quarterly instalments, and very large companies can face payment dates much earlier in their accounting periods.

The safest approach is to treat Corporation Tax as an ongoing financial obligation rather than an annual administrative task. Know your accounting period. Record your payment deadline. Estimate your taxable profit regularly. Keep the tax money available. And remember that your HMRC tax deadline and Companies House filing deadlines are separate obligations.

For founders, particularly those running UK companies from overseas, getting this distinction right can make the difference between a well-managed business and an avoidable compliance problem.