Corporation Tax Deadlines & Payments — A Trade Limited Company's Guide (2026)

Your Accounting Period and Financial Year

Corporation Tax is charged on the profits your company makes in its accounting period. For most established trade companies, the accounting period is 12 months long and matches your company's financial year — the period your annual accounts cover. When you incorporated, Companies House set your accounting reference date (usually the last day of the month you registered), and your year end normally falls on that date each year.

In your first year there's a quirk: your first set of accounts often covers slightly more than 12 months, which means HMRC splits it into two accounting periods for Corporation Tax — one of 12 months and a short one for the remainder. Each period has its own pay and file deadlines. After year one, things settle down and your accounting period normally runs as a clean 12 months ending on your year-end date. Throughout this guide we assume a standard 12-month period ending 31 March.

Registering for Corporation Tax

When you start trading — taking on work, buying materials, advertising, earning income — you must register for Corporation Tax with HMRC within 3 months of that point. "Starting to trade" is not the same as incorporating your company; you might form the company weeks before you pick up your first job. The clock starts when business activity begins.

You register online through your HMRC business tax account using your company's Unique Taxpayer Reference (UTR), which HMRC posts to your registered office shortly after incorporation. Miss the 3-month window and you can be charged a penalty, so register as soon as the tools come out and the first invoice goes out.

The Payment Deadline Comes First

Here is the part that trips everyone up. For a company with profits under £1.5 million — which covers the overwhelming majority of sole-director and small trade limited companies — Corporation Tax is due 9 months and 1 day after the end of your accounting period.

So for a 31 March year end, your payment deadline is 1 January the following year. You must have the money with HMRC by then, even though you have a further three months before the return itself is due. In practice this means you and your accountant need to know your tax figure well before the year is fully closed off in formal accounts. Most accountants prepare the numbers early precisely so you can pay on time.

The lesson: do not wait until the filing deadline to think about Corporation Tax. Set money aside through the year — many trade directors move a percentage of every payment received into a separate tax pot — so the January bill does not wipe out your cash flow.

The Filing Deadline

You must file your CT600 company tax return with HMRC within 12 months of the end of your accounting period. For a 31 March year end, that means the return is due by 31 March the following year — a full three months after the tax was paid.

The CT600 reports your taxable profit and the Corporation Tax due, and it must be accompanied by your company accounts and the tax computations. Even if your company made a loss or no profit, you still have to file a return — a nil return is still a return, and the penalties for not filing apply regardless of whether tax is owed.

How to Pay HMRC

There is no payment booklet for Corporation Tax — HMRC stopped issuing them. You pay online (or by bank transfer) using your 17-character Corporation Tax payment reference, which is specific to the accounting period you're paying for. Using the wrong reference, or last year's reference, can mean your payment is misallocated, so check it carefully each year.

Crucially, allow time for the payment to clear. Faster Payments are usually same-day, but other methods can take three working days or more. If the deadline lands on a weekend or bank holiday, make sure the cleared funds reach HMRC on the last working day beforehand. Payment methods include:

• Online or telephone banking via Faster Payments, CHAPS or Bacs
• Direct Debit set up through your HMRC online account
• Debit or corporate credit card online
• At your bank or building society (with a paying-in slip from HMRC if you have one)

Quarterly Instalments for Large Companies

Companies with profits over £1.5 million pay Corporation Tax in quarterly instalments rather than as a single annual payment, with the first instalment due before the accounting period has even ended. The £1.5 million threshold is divided by the number of associated companies, which can pull smaller groups into the regime.

For practical purposes, most trade limited companies will never hit this. A typical electrical, building or plumbing Ltd with one or two directors operates well under the threshold and pays the single 9-months-and-1-day deadline described above. If your profits are approaching £1.5 million, that is exactly the point at which you should be taking proper accountancy advice anyway.

What Happens If You Miss a Deadline

HMRC treats late filing and late payment separately, and you can be hit by both at once.

Late filing penalties

Miss the CT600 filing deadline and the penalties escalate:

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

If your return is late three times in a row, the £100 penalties increase to £500 each. These penalties apply even if the company owes no tax.

Interest on late-paid tax

If you pay your Corporation Tax late, HMRC charges interest on the outstanding amount from the day after the due date until it is paid. The rate moves with the Bank of England base rate, so it is not trivial. Interest is charged separately from filing penalties — late payment and late filing are two different failures.

Penalties for errors

Getting the figures wrong carries its own penalties. If HMRC finds your return is inaccurate, the penalty depends on whether the error was careless, deliberate, or deliberate and concealed — ranging from a small percentage of the extra tax for a careless mistake up to 100% for deliberate and concealed errors. Keeping clean records and using proper job-costing software through the year is the best defence against an error penalty.

Companies House Is a Separate Deadline

Do not confuse your HMRC obligations with your Companies House ones — they are different filings with different deadlines. You file annual accounts with Companies House as well as a CT600 with HMRC, and the accounts you send to each can differ in detail.

For an established private company, the Companies House accounts deadline is 9 months after your year end — for a 31 March year end that's 31 December. Note that this is earlier than your 12-month HMRC filing deadline, and it lands close to your Corporation Tax payment date. You also file an annual confirmation statement with Companies House, which is a separate requirement again. Missing the Companies House accounts deadline triggers its own automatic late filing penalties, starting at £150 and rising the longer you delay.

Worked Example — 31 March Year End

Say your trade limited company has an accounting period running from 1 April 2026 to 31 March 2027. Here is how the key dates fall, in the order they actually happen — note that the payment and the Companies House accounts both come before the HMRC return.

Read down that table and the trap is obvious: you pay HMRC on 1 January 2028, but the return that calculates the bill is not due until 31 March 2028. The money goes out first, the paperwork follows. If your year end is a different date, shift every row accordingly — the gaps between them stay the same.

Staying on Top of It

The directors who never get caught out treat Corporation Tax as a year-round job, not a January scramble. Three habits make the difference:

• Save as you earn. Move a fixed percentage of every payment received into a separate tax account so the bill is already covered when 1 January arrives.
• Get your accounts done early. Ask your accountant to prepare the figures well before the payment deadline, not the filing deadline — you need the number to pay it.
• Keep clean records. Accurate, itemised job costs and expenses through the year reduce the risk of errors, make the CT600 quicker to file, and protect you from error penalties.

Corporation Tax is unforgiving of disorganisation but entirely manageable with a system. Know your year-end date, mark the pay and file deadlines in your calendar the moment your accounting period opens, and set the money aside as it comes in. Always confirm the exact figures and dates for your company with your accountant — this guide is general information for 2026, not advice.