31 March year end: your 31 December accounts deadline and 1 January Corporation Tax payment

This page assumes a private limited company with a 31 March 2026 year end that is not filing its first accounts. For another year end, use the deadline checker. The wider rules are in When are company accounts due?.

The three dates for a year to 31 March 2026

Two of the dates sit one day apart, in the holiday week. The tax is due before the return, so you need the tax figure when you prepare the accounts.

What to file by 31 December 2026

A private company has 9 months after the end of its accounting reference period to deliver its accounts to Companies House¹. For a year ending on 31 March 2026, that is Thursday 31 December 2026.

Companies House charges an automatic penalty if the accounts are late⁶:

The penalty doubles if your accounts are late two years in a row⁶. Companies House lists reasons an appeal may not succeed. They include that these are your first accounts, that the company is dormant, that another director is responsible for filing, that the delay was your accountant’s fault, and that you did not know when or how to file⁶.

If you can’t make the deadline for a reason outside your control, you must apply for more time before it passes. The law caps any extension at 12 months after the end of the accounting reference period¹. See the extension guide.

If this is your first set of accounts

The 9-month rule is for later years. If the first accounting reference period is longer than 12 months, the deadline is the later of two dates: 9 months after the first anniversary of incorporation, or 3 months after the period ends¹. When are company accounts due? works through a first-accounts example.

Paying Corporation Tax by 1 January 2027 (and the bank holiday)

For profits up to £1.5 million, you must pay Corporation Tax 9 months and 1 day after the accounting period ends². For a period ending on 31 March 2026, that is Friday 1 January 2027. Companies with profits over £1.5 million pay in instalments instead².

That day is a bank holiday⁷. GOV.UK says that if the deadline falls on a weekend or bank holiday, your payment must reach HMRC on the last working day before it, unless you pay by Faster Payments using online or telephone banking². The last working day before 1 January 2027 is Thursday 31 December 2026. Christmas Day and the substitute Boxing Day holiday on 28 December also fall in the run-up⁷.

GOV.UK gives these processing times²:

You can’t pay Corporation Tax by post². GOV.UK advises choosing a method that allows enough time for your payment to clear².

In practice, a Faster Payment is the safest choice for a deadline on 1 January. If you would rather use Bacs or a new Direct Debit, start well before Christmas. HMRC may charge interest on tax paid after the deadline².

The CT600 by 31 March 2027

The deadline for the return is 12 months after the end of the accounting period it covers³. For a year ending on 31 March 2026, that is Wednesday 31 March 2027.

You have to file once HMRC sends a notice to deliver a Company Tax Return. You must still send one if you make a loss or have no Corporation Tax to pay³. The Corporation Tax profit or loss can differ from the profit or loss in your annual accounts³.

For a return due on or after 1 April 2026, HMRC’s late filing penalty is £200, with another £200 at 3 months. At 6 months HMRC estimates the tax and adds 10% of the unpaid tax, and another 10% at 12 months. If the return is late three times in a row, the £200 penalties become £1,000 each^4,5. This return is due on 31 March 2027, so these amounts apply.

How to send the return now that the free HMRC service has gone is covered in the CATO replacement guide.

Dormant? Your accounts are still due

A dormant company still files annual accounts and a confirmation statement⁸. So the accounts date is the same: 31 December 2026. If the company is dormant for Companies House and qualifies as small, it can file dormant accounts and leave out the auditor’s report⁸.

The Corporation Tax side is lighter. If you have filed a Company Tax Return before or received a notice to deliver one, file a return showing the company was dormant for that period. After HMRC knows the company is dormant, you don’t need another return unless you get a further notice⁸. See Dormant companies: what counts and what you still file.

A community interest company has the same year-end dates. See CIC annual filings for its extra report.

Leaving it late: what still works in the last week

• Pay the tax by Faster Payment. It is the one method GOV.UK exempts from the “last working day before” rule on a bank holiday, and it normally arrives the same or next day².
• File the accounts first, then the return. The accounts are due on 31 December and the CT600 months later, so don’t hold up the accounts while you finish the tax calculation. The tax payment is the date with the least slack.
• Don’t count on an appeal. A penalty for late accounts is automatic, and most of the common reasons are listed as unlikely to succeed⁶.
• Apply for more time before the deadline, not after. The application must be made before the period expires¹.

A late payment is not the same as a late return. They have separate penalties, and paying on time does not excuse a late CT600^2,4.

Do it with Fileyear

Fileyear prepares the accounts and the Company Tax Return for a limited company: accounts and tax return, £70.80 in total. It is free to prepare.