Corporation Tax deadlines for small limited companies: a UK guide

Most small UK limited companies must pay Corporation Tax 9 months and 1 day after the end of their accounting period and file their Company Tax Return (CT600) within 12 months of the end of that period. So yes – you pay before the return is due. Miss either date and HMRC charges penalties or interest automatically.

This guide explains every Corporation Tax deadline a small company needs to know, with worked examples, the rules for your first year and the current rates.

Corporation Tax deadlines at a glance

The payment deadline above applies to companies with taxable profits under £1.5 million. Larger companies pay in quarterly instalments.

Want your exact dates? Use our free company accounts deadline calculator.

When is Corporation Tax due?

Corporation Tax is due 9 months and 1 day after your accounting period ends. When the period ends on the last day of a month, the payment is due on the 1st of the tenth month after it.

HMRC won’t send you a bill. You need to work out what you owe (or have your accountant do it) and pay using your 17-character Corporation Tax payment reference.

When is the Company Tax Return (CT600) due?

Your Company Tax Return is due 12 months after the end of the accounting period it covers. For a year ending 31 March 2026, the CT600 deadline is 31 March 2027.

The return must be filed online and includes:

• the CT600 form itself
• your company’s full statutory accounts
• a Corporation Tax computation showing how the taxable profit was worked out

Even if your company made a loss or owes no tax, you still have to file a return if HMRC has sent you a “notice to deliver a Company Tax Return”.

Why you pay before you file

It surprises a lot of new directors, but the payment deadline comes three months before the filing deadline. In practice, that means you can’t leave your year-end until the last minute: your accounts and tax computation need to be ready in time to know how much to pay.

A simple rule of thumb: aim to have your year-end accounts finished within 6 months of your year-end. You’ll know your tax bill with plenty of time to spare, and your Companies House accounts will be ready too.

Your first year: often two accounting periods

A company’s first set of accounts usually covers more than 12 months – for example, a company registered on 12 June 2025 has a first year-end of 30 June 2026. But an accounting period for Corporation Tax can’t be longer than 12 months.

So HMRC splits that first long period into two:

1. 12 June 2025 to 11 June 2026 – the first 12 months
2. 12 June 2026 to 30 June 2026 – the short period that’s left

Each period has its own Corporation Tax payment deadline (12 March 2027 and 1 April 2027 in this example) and its own CT600. Both returns are due 12 months after the end of the accounts period – 30 June 2027 here. Our deadline calculator works this out for you if you choose “first accounts”.

Corporation Tax rates for 2026/27

Marginal relief means a company with profits between £50,000 and £250,000 pays an effective rate somewhere between 19% and 25%. The £50,000 and £250,000 limits are reduced if your accounting period is shorter than 12 months or if your company has associated companies.

Penalties and interest for missing the deadlines

Late payment: HMRC charges interest from the day after the payment deadline until you pay. The rate is the Bank of England base rate plus 4%.

Late Company Tax Return:

• 1 day late: £100
• 3 months late: another £100
• 6 months late: HMRC estimates your tax bill and adds a penalty of 10% of the unpaid tax
• 12 months late: another 10% of the unpaid tax

If your return is late three times in a row, the £100 penalties go up to £500 each. Companies House charges separate penalties if your annual accounts are late, starting at £150 – see GOV.UK’s guidance on Company Tax Return penalties for the full detail.

How to never miss a Corporation Tax deadline

• Know your dates. Put your year-end, payment date and CT600 deadline in your calendar the day your financial year ends.
• Keep your books up to date. Year-end is far quicker when your records are already in order – see our bookkeeping routine for small limited companies.
• Put tax money aside. Moving roughly a fifth of your profit into a separate savings account each month means the bill is never a shock.
• Get your accounts done early. Finishing within 6 months gives you time to plan, claim everything you’re entitled to and pay on time.

Frequently asked questions

Do I pay Corporation Tax if my company made a loss?

No. If your company made a loss there’s no Corporation Tax to pay, but you still need to file a Company Tax Return if HMRC has sent you a notice to file. The loss can usually be carried forward to reduce future tax bills.

Is the Corporation Tax deadline the same as the Companies House deadline?

No. Companies House needs your annual accounts 9 months after your financial year-end. HMRC needs your Corporation Tax payment 9 months and 1 day after the accounting period ends, and your CT600 12 months after. They’re separate deadlines with separate penalties.

Can I pay Corporation Tax early?

Yes. You can pay as soon as you know how much you owe. Paying early doesn’t change your filing deadline, and HMRC may pay a small amount of interest on tax paid early.

Does a dormant company pay Corporation Tax?

Not usually. A dormant company isn’t trading, so it normally has no Corporation Tax to pay and doesn’t need to file a CT600 unless HMRC asks for one. Read our guide on how to make a company dormant.

Let us take care of it

At PeekaBooks we prepare your year-end accounts and file them with Companies House and HMRC for a fixed fee – £199 for non-VAT-registered limited companies, or £99 if your turnover is under £5,000. No hidden extras, no jargon – just your deadlines met.