Corporation Tax deadlines: when to pay and when to file

A UK limited company has three separate year-end deadlines, and they don't fall in the order most people expect. The tax has to be paid three months before the tax return has to be filed, and the Companies House accounts deadline is different again. Enter your year end below to get all three dates, then read on for how each one works and what happens if you miss it.

The three deadlines at a glance

For a 31 December 2025 year end, the same rules give: accounts to Companies House by 30 September 2026, tax paid by 1 October 2026, and the CT600 filed by 31 December 2026.

Paying: 9 months and 1 day

If your company's taxable profits are £1.5 million or less, the whole Corporation Tax bill for the accounting period is due 9 months and 1 day after the period ends. There's no payment on account and no instalments. It's one payment, and HMRC doesn't send a bill. You're expected to work out the amount (or have your accountant do it) and pay it on time, even if you haven't filed the return yet.

Where a year end is the last day of a month, the deadline follows the month end: a 30 June year end means paying by 1 April, not 31 March. If the deadline falls on a weekend or bank holiday, HMRC says your payment must reach it on the last working day before, unless you pay by Faster Payments. Allow three working days for Bacs and a few days for Direct Debit.

You pay using your company's 17-character payment reference, which is based on your Unique Taxpayer Reference (UTR) and is different for each accounting period. Using last year's reference is a common way for a payment to end up in the wrong place.

Filing the CT600: 12 months

The Company Tax Return (form CT600, plus your accounts and tax computations) is due 12 months after the accounting period ends. You still have to file even if the company made a loss or has no tax to pay. If HMRC has sent a "notice to deliver a Company Tax Return", you must respond to it even for a dormant period.

Because payment is due three months earlier, the practical deadline for doing your figures is the payment date, not the filing date. Many companies file both at the same time for that reason.

Companies House accounts: 9 months

Your annual accounts go to Companies House, which is a separate body from HMRC with its own deadline: 9 months after your accounting reference date (your year end) for a private company. This is usually the first of the three deadlines to arrive.

First accounts are different. For a new company, the first accounts are due 21 months after the date of incorporation, not 9 months after the first year end. The first accounting period can also be longer than 12 months, but a Corporation Tax accounting period can't be. HMRC splits a long first period into two: the first 12 months, and the rest. Each has its own payment deadline. The CT600 for both is due 12 months after the end of the full period covered by the accounts.

Large companies: quarterly instalments

If taxable profits are over £1.5 million, the company doesn't get the 9-month wait. It pays in four quarterly instalments, based on its estimated bill for the year. For a 12-month accounting period, the first is due 6 months and 13 days after the period starts, then every 3 months after that. So if your year starts on the 1st of a month, they fall on the 14th of the 7th, 10th, 13th and 16th months. For a year running from 1 April 2026 to 31 March 2027, that's 14 October 2026, 14 January 2027, 14 April 2027 and 14 July 2027.

A company isn't treated as large in the first year it crosses £1.5 million, as long as its profits are no more than £10 million and it wasn't large the year before. Companies with profits over £20 million ("very large") pay even earlier, starting 2 months and 13 days after the period starts (the 14th of the 3rd, 6th, 9th and 12th months for a year starting on the 1st), so the whole bill is paid within the year. Both thresholds are divided between associated companies, so a group of companies can reach them much sooner than you'd expect. For how associates affect your rates too, see how UK Corporation Tax works.

What happens if you miss a deadline

Paying late. HMRC charges late payment interest from the day after the deadline until the day you pay. The rate is the Bank of England base rate plus 4% (it was base rate plus 2.5% before April 2025). There's no fixed penalty for paying late, but the interest adds up quickly on a large bill.

Filing the CT600 late. Penalties are automatic:

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

If your return is late three times in a row, the £100 penalties go up to £500 each.

Filing accounts late at Companies House. For a private company, the penalty is £150 if up to 1 month late, £375 if up to 3 months, £750 if up to 6 months and £1,500 if more than 6 months late. It doubles if your accounts were also late the year before. These amounts can change, so check GOV.UK's late filing penalties page for the current figures.

Other dates to put in the diary

• Registering for Corporation Tax: within 3 months of starting to trade.
• Confirmation statement: at least once every 12 months, filed at Companies House within 14 days of the end of the review period.
• VAT returns: usually quarterly, 1 month and 7 days after the end of each VAT period, if you're registered. See how to work out VAT.
• Directors' Self Assessment: if you take dividends, your personal tax return is due by 31 January after the end of the tax year.

Common mistakes

Working to the filing deadline instead of the payment deadline. The tax is due three months before the return. Leaving your accounts until month 11 means paying late interest, or paying an estimate and then correcting it.

Mixing up HMRC and Companies House. They are two separate bodies with separate deadlines, logins and penalties. Filing with one doesn't count for the other, although some accounting software does both at once.

Spending the tax money. The cash in the company account isn't all yours. Setting aside roughly 19–25% of profit as you go makes the payment date a non-event.

Using the wrong payment reference. Each accounting period has its own reference. A payment against the wrong period can show as unpaid and start interest running.

Related guides and calculators

• How UK Corporation Tax works: the 19% and 25% rates, marginal relief and associated companies.
• Corporation Tax calculator: estimate the bill for 2026/27.
• How self-employment tax works: the deadlines if you trade as a sole trader instead.
• VAT calculator: add or remove UK VAT.

Frequently asked questions