Limited company tax return deadline: when to file and what late filing costs

Your limited company's tax return (form CT600) is due 12 months after the end of the accounting period it covers. Corporation Tax is paid earlier, nine months and one day after the period ends. File late and HMRC charges a £200 penalty the next day, even if your company owes no tax.

Two rules changed in spring 2026. Late filing penalties doubled for returns due on or after 1 April 2026, and HMRC's free online filing service closed on 31 March 2026, so every return now goes through commercial software (Closure of the service to file your company accounts and tax return on GOV.UK, checked 12 October 2026).

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When is the company tax return due?

Your Company Tax Return is due 12 months after the end of the accounting period it covers. You pay the Corporation Tax before that: nine months and one day after the period ends.

So for most companies, the order is pay first, file second. You work out the final bill when you prepare the return, so in practice you need the return's figures ready by the payment date. Our guide to when Corporation Tax is due covers payment dates, and the quarterly instalments that companies with profits above £1.5m pay instead.

Your accounting period for Corporation Tax is normally the same 12 months as your annual accounts, but it can differ, especially in your first year. You can check its dates in your HMRC business tax account.

Two rules can move the date:

• If HMRC's 'notice to deliver a Company Tax Return' reaches you late, the deadline is three months from the date of the notice, if that's later than the usual date.
• If your first accounts cover more than 12 months, you file two returns (see the first-year section below).

Your annual accounts are a separate job with a separate deadline. You file your annual accounts with Companies House nine months after your financial year ends, or 21 months after registration for your first accounts.

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Company tax return filing dates by year-end

Take the last day of your accounting period and add 12 months: that's your filing deadline. The table shows the dates for common 12-month periods.

These dates follow gov.uk's 12-month rule. Confirm your own period in your HMRC business tax account, and check it against the notice HMRC sends you.

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Your first year can mean two tax returns

An accounting period for Corporation Tax can't be longer than 12 months. If your first accounts cover more, you file two returns, both due 12 months after the end of those first accounts.

First accounts often run longer than a year, because they start on the day the company is set up and end on the accounting reference date Companies House sets. gov.uk's example is a company set up and trading from 11 May 2024, with first accounts to 31 May 2025 (Your limited company's first accounts and Company Tax Return on GOV.UK):

Both returns share the same filing date. The law sets it as the latest of 12 months after the return's own period and 12 months after the end of the accounts, where those accounts cover 18 months or less. Each return still has its own payment date, and the first one falls earlier.

If your company didn't trade straight away, it may have been dormant for Corporation Tax before it started. Whether that means one return or two depends on when you added Corporation Tax to your business tax account, so check gov.uk's guide for your case.

Changing your year-end later can have the same effect. If you lengthen your financial year, your accounts cover more than 12 months, so you file two returns, and you must update your accounting period with HMRC before the original filing date. In gov.uk's example, a year-end of 31 December 2024 moved to 31 March 2025 means telling HMRC before 31 December 2025 and filing all returns by 31 March 2026. Miss the update and you may get a late filing penalty.

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Late filing penalties start at £200 on day one

HMRC charges £200 the day after the deadline and another £200 at three months, even if there's no tax to pay. At six and 12 months, it adds 10% of any unpaid tax each time.

These amounts apply to returns with a filing date on or after 1 April 2026. Before that, the fixed penalties were £100, and £500 for repeat late filers (Corporation Tax: increases to late filing penalties on GOV.UK, 26 November 2025).

If your return is late three times in a row, the £200 penalties rise to £1,000 each, so £2,000 by three months (Company Tax Returns: penalties for late filing on GOV.UK).

A tax determination is HMRC's own estimate of what you owe once the return is six months late. You can't appeal against it. To replace it, file the return and pay the tax due. HMRC then recalculates the interest and penalties.

Paying late costs extra on top. HMRC charges interest on unpaid Corporation Tax from the day after the payment deadline, at base rate plus 4%, which is 7.75% from 9 January 2026 (HMRC interest rates for late and early payments on GOV.UK).

Companies House fines late accounts separately. For a private limited company, the penalty runs from £150 to £1,500 depending on how late they are, and it doubles if your accounts are late two years in a row (Penalties for late filing of annual accounts on GOV.UK).

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How to appeal a late filing penalty

If you had a reasonable excuse, you can appeal a late filing penalty online, but only once you've filed the return. You usually have 30 days from the date the penalty was issued (Disagree with a penalty on GOV.UK).

To appeal:

1. File the overdue Company Tax Return.
2. Gather your company's Unique Taxpayer Reference (UTR), the date on the penalty notice, the penalty amount, and the end date of the accounting period it's for.
3. Complete HMRC's online appeal form in one go, explaining why the return was late. You can't save it and come back.
4. Print the form and post it to the address it gives.

gov.uk says a reasonable excuse can include (Reasonable excuses on GOV.UK):

• A close relative's death shortly before the deadline.
• An unexpected stay in hospital, or a serious illness.
• Your computer or software failing while you prepared the return, or problems with HMRC's online services.
• A fire, flood, or theft that stopped you completing the return.
• Relying on someone else to send the return when they didn't.

It won't accept these:

• A payment that failed because there wasn't enough money.
• Finding HMRC's online system too hard to use.
• Not getting a reminder from HMRC.
• A mistake on your return.

Whatever the excuse, you need to file as soon as you're able to. If HMRC doesn't change its decision, you can ask for a review or take the appeal to the tax tribunal.

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How to file your company tax return

You file online, using commercial software or an accountant. HMRC's own free filing service closed on 31 March 2026. The return is the CT600 form plus your accounts and tax computations, tagged in a format called iXBRL.

You can only file a paper return if you have a reasonable excuse or you're filing in Welsh (Closure of the service to file your company accounts and tax return on GOV.UK). Filing your accounts with Companies House doesn't file them with HMRC: they're separate submissions.

The steps:

1. Check your accounting period dates in your HMRC business tax account.
2. Prepare your statutory accounts, then the tax computation. This works out your profit for Corporation Tax, which is different from the profit in your accounts.
3. Complete the CT600, with any supplementary pages your company needs.
4. File the CT600, accounts, and computations together through software that produces iXBRL, or ask your accountant to file for you (Businesses XBRL guide on GOV.UK).

HMRC publishes the list of commercial software for filing your Company Tax Return on GOV.UK. It shows what each product can file and whether it suits self-filers. HMRC doesn't recommend any one product, so check that the software you choose can file all three parts.

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If you can't pay the bill, file on time anyway

File on time even if you can't pay yet: late filing and late payment are charged separately. Talk to HMRC before the payment deadline, then compare Time to Pay with borrowing.

Our guide to how to pay Corporation Tax covers the payment methods and what to do if the cash isn't there. In short, an HMRC Time to Pay arrangement lets your company spread the bill in instalments if HMRC agrees the plan is affordable, and interest keeps running on what's unpaid (If you cannot pay your tax bill on time on GOV.UK). A business loan can pay HMRC on the due date if the cash is on its way, but it costs interest and fees. We compare the two in Time to Pay or a business loan.

If you're weighing up borrowing, here's how an iwoca Flexi-Loan works. We lend to UK limited companies, from £1,000 to £1 million over up to five years, with a decision within 24 hours. You can repay early with no fees. Every new Flexi-Loan needs a personal guarantee from at least one director.

Overdue tax can show up in credit checks and count against an application. Borrowing only makes sense if the repayments fit your cash flow. If they don't, Time to Pay is likely to suit your company better.

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Company tax return deadline: FAQs

Do I have to file if my company made a loss or owes no tax?

Yes. If HMRC has sent a 'notice to deliver a Company Tax Return', you must file even if the company made a loss or has no Corporation Tax to pay, and the late filing penalties still apply (Company Tax Returns on GOV.UK).

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Does a dormant company need to file a tax return?

Only if HMRC asks. If you've had a notice to deliver a return, file it to show the company was dormant. Once you've told HMRC the company is dormant, you don't file again unless you get another notice. You still file annual accounts and a confirmation statement with Companies House (Dormant for Corporation Tax on GOV.UK).

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Can I get an extension on the company tax return deadline?

There's no automatic extension. The deadline is only later if HMRC's notice reached you late, in which case you have three months from the notice. If something outside your control made you late, file as soon as you can and appeal with a reasonable excuse.

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What if HMRC hasn't sent a notice to deliver a return?

If your company has Corporation Tax to pay, tell HMRC within 12 months of the end of the accounting period. If you don't, HMRC can charge a 'failure to notify' penalty based on the unpaid tax (Corporation Tax penalties on GOV.UK).

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Can I file the company tax return myself?

Yes. gov.uk says you can do it yourself or use an accountant. You'll need software that can file the CT600, the tax computation, and your accounts in iXBRL, and HMRC's software list shows which products suit self-filers. An accountant can help if your company claims reliefs, needs supplementary pages, or is part of a group.

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Can I change a return after filing it?

Usually, yes, within 12 months of the filing deadline, using your software or by writing to HMRC. After that, you can still claim back overpaid tax through overpayment relief, and you should tell HMRC about underpaid tax using its online disclosure service. HMRC may charge a penalty for errors, which is one of several other HMRC penalties (Company Tax Returns: making changes on GOV.UK).

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How do I make sure I don't miss the deadline?

Put the payment date and the filing date in your calendar the day your year ends. Because you need the final tax figure to pay at nine months and one day, aim to finish the return then too, and file it with your Companies House accounts.

Sources (all checked 12 October 2026):

• Company Tax Returns on GOV.UK
• Company Tax Returns: penalties for late filing on GOV.UK
• Corporation Tax: increases to late filing penalties on GOV.UK
• Closure of the service to file your company accounts and tax return on GOV.UK
• Your limited company's first accounts and Company Tax Return on GOV.UK
• Finance Act 1998, Schedule 18, paragraph 14 on legislation.gov.uk