Check your Corporation Tax deadlines

Corporation Tax has three separate deadlines: registering, paying and filing. They do not fall on the same date, which is why many companies get caught out. This guide explains each one.

1. Register within 3 months of starting to trade

A new limited company must register for Corporation Tax with HMRC within 3 months of starting to do business. "Doing business" includes buying, selling, advertising, employing someone or renting property – not just receiving your first payment.

After you register, HMRC will send letters with your Unique Taxpayer Reference (UTR) and, later, a notice to deliver a Company Tax Return.

Accounting periods: why they matter

Corporation Tax is worked out for each accounting period, which is usually the same as your financial year and cannot be longer than 12 months.

In your first year this can be confusing. Your first accounts filed at Companies House can cover more than 12 months, but for tax this is split into two accounting periods: the first 12 months, then the remaining period. Each has its own tax return and payment date.

2. Pay 9 months and 1 day after the end of the period

For most companies, Corporation Tax must be paid 9 months and 1 day after the end of the accounting period.

Example: if your accounting period ends on 31 March 2026, payment is due by 1 January 2027.

Points to note:

• You usually pay before the tax return is due.
• HMRC does not send a bill. You work out what is owed (or your accountant does) and pay it.
• If the deadline falls on a weekend or bank holiday, pay by the last working day before it, unless you use Faster Payments.
• Use the correct 17-character payment reference for that accounting period.
• Late payments are charged interest.

Larger companies with taxable profits over £1.5 million pay in instalments during the year instead. Different rules apply above £20 million.

3. File your Company Tax Return within 12 months

Your Company Tax Return (form CT600) is due 12 months after the end of the accounting period it covers.

You must file even if the company made a loss or has no tax to pay, once HMRC has sent a notice to deliver a return. The return includes the company's taxable profit or loss and the tax due, which can differ from the profit in your accounts.

Late filing penalties

For returns with a filing date on or after 1 April 2026, the fixed penalties are:

• 1 day late: £200
• 3 months late: another £200
• 6 months late: HMRC estimates the tax bill and adds a penalty of 10% of the unpaid tax
• 12 months late: another 10% of any unpaid tax

If the return is late three times in a row, each £200 penalty rises to £1,000.

Corporation Tax rates

For reference, the current rates are 19% on profits of £50,000 or less, 25% on profits over £250,000, and marginal relief in between. The limits are reduced for short accounting periods and associated companies.

Do not confuse these with Companies House deadlines

Companies House has its own deadlines:

• Annual accounts: your first accounts are due 21 months after incorporation, then 9 months after each year end.
• Confirmation statement: at least once every 12 months.

Missing these brings separate Companies House penalties. A dormant company still needs to file accounts and a confirmation statement – see our Dormant Company Accounts service.

Simple steps to never miss a deadline

1. Note your accounting reference date and each accounting period.
2. Put the payment and filing dates in your calendar as soon as the period ends.
3. Set aside money for tax each month, so the bill is not a shock.
4. Keep good records throughout the year.
5. Ask your accountant to confirm the dates for your first, split year.

How Form My Company can help

Every formation package includes Corporation Tax registration with HMRC, so you start on time. Our Annual Accounts service prepares your accounts and Company Tax Return, and our Bookkeeping, VAT and Payroll service keeps your records up to date through the year. If your company is not trading, we can prepare dormant accounts too.

Frequently asked questions