Limited company tax return deadline: key dates and penalties

When you're running a limited company, one of your non-negotiables is staying on top of your tax obligations. Understanding the limited company tax return deadline, filing correctly, and avoiding penalties are essential to keeping your business on the right side of HMRC.

Let’s break down what you need to know, how to make the process smoother  (especially if costs are tight when the deadline approaches) and how to get a business loan to pay your tax bill (should you need it).

What is a limited company tax return and why is it important?

A company tax return is an official report sent to HMRC each year that outlines your business’s income, expenses, profits, and tax owed. You’ll usually submit this using a form called a CT600, alongside your company’s financial accounts and tax calculations.

Filing your tax return on time is a legal requirement. Mistakes, missed deadlines or failing to report can lead to penalties and further HMRC scrutiny. 

There’s also a practical side to filing your return accurately. Staying on top of your taxes gives you and others a clear picture of how your company is performing.

When is the limited company tax return deadline in the UK?

Your limited company tax return deadline falls 12 months after your company’s accounting year-end. But there’s some nuance here: Corporation Tax payments must be paid within nine months and one day after the end of your accounting period.

So, if your year ended on 31st March, your Corporation Tax payment is due by 1st January.

Corporation Tax is the actual tax your limited company owes on its profits. While the limited company tax return (filed using the CT600 form) is the official document you submit to HMRC to declare those profits and show how you worked out what Corporation Tax is due.

They’re part of the same process, but the tax return is the report, and Corporation Tax is the bill. So, you:

• Calculate and pay the Corporation Tax owed (by 9 months and 1 day after the end of the same period).
• File the tax return (by 12 months after the end of your accounting period),

This is all separate from your Companies House filing deadline, which is for submitting your company’s annual accounts. It’s easy to confuse the two, but they are handled by different bodies and have different rules.

HMRC handles Corporation Tax and the CT600, while Companies House deals with financial accounts and company records.

What happens if you miss the company tax return deadline?

Miss the limited company tax return deadline, and you’ll get an automatic £100 fine (even if your company doesn’t owe any tax).

Leave it three months, and there’ll be another £100 fine. After six months, HMRC may estimate your tax bill (usually not in your favour) and slap on a 10% surcharge. At twelve months overdue, another 10% surcharge is added.

If you make a habit of filing late, you could face harsher fines, and HMRC may even begin investigating your company more closely. It’s not just the financial hit: The time and stress involved in sorting out late returns can be damaging in their own right.

What is the penalty for filing my company tax return late?

Filing your company tax return late can quickly become costly: HMRC issues a £100 fine after just one day, another £100 if you’re three months late, and adds 10% of any unpaid Corporation Tax at six months, plus another 10% after 12 months. On top of that, HMRC charges interest on late payments, which is separate from these penalties. Even short delays can escalate, especially if your business is already managing tight cash flow.

How to prepare and file your company tax return on time

Start by making sure you’ve got an HMRC online account set up for Corporation Tax. If you’ve not done this before, it can take a few days to receive your activation code. So don’t leave it until the last minute.

Next, gather your records: Invoices, bank statements, expense reports, and anything else that shows your company’s financial activity. If you’re VAT-registered, include your VAT returns too.

You’ll – or your accountant – will then complete the CT600 form online via HMRC’s website. Once submitted, it’s worth keeping an eye on your messages in case HMRC gets in touch with questions.

Giving yourself breathing room before the deadline means you can respond and make corrections if needed.

Common mistakes to avoid when filing your company tax return

Depending on the nature and set up of your business, corporation tax can be more or less complicated – but even if your affairs are simple it can be easy to make a mistake. Make sure to watch out for:

• Mixing up Companies House and HMRC deadlines.
• Misjudging deductible expenses or forgetting depreciation rules.
• Skipping supplementary pages if you’ve got a more complex company structure.
• Waiting until the last moment to get started (especially if you rely on an accountant or bookkeeper).

Can you change your company’s accounting period to match the tax year?

Yes, you can change your company’s accounting period. Many businesses choose to align it with the tax year (ending 5th April) or the UK government’s fiscal year (ending 31st March) to simplify bookkeeping and help with year-on-year comparisons.

To do this, you’ll need to apply to Companies House to change your accounting reference date.

You can either shorten or extend your accounting period, though HMRC has specific rules if you want to change the tax payment dates. So make sure to read the guidance carefully or speak with an accountant.

Should you hire an accountant for your company tax return?

For many company directors, the answer is yes. While some small companies with straightforward finances might manage alone, most find that hiring an accountant brings peace of mind and real value.

Accountants ensure your tax return is accurate and compliant, identify legal ways to reduce your Corporation Tax liability, and can even spot red flags or inefficiencies in your finances.

The cost of hiring one is often offset by the time you save and the savings they uncover.

Do I need an accountant to file my company tax return?

Legally, no. You can file it yourself, provided you’re confident in your accounting knowledge and up to speed on HMRC rules.

But the risk of costly errors makes most company owners think twice. Affordable options do exist, like digital bookkeeping software bundled with accountant support. 

Best tools and software for managing tax returns efficiently

The right tools make a big difference. HMRC-recognised software like Xero, QuickBooks, and FreeAgent helps you track income, expenses, and prepare for your limited company tax return deadline with less stress.

These cloud-based platforms connect to your bank accounts, making it easier to automate invoicing and track deductible expenses. Many are already integrated with HMRC’s Making Tax Digital (MTD) initiative (which’ll do away with paper returns), meaning you’ll be set up for future compliance too.

Worried about tax bills? A flexible solution from iwoca

Sometimes, even if you’ve got everything filed on time, the tax bill itself can be a challenge, especially during tight months.

That’s where a short-term tax loan could help. At iwoca, we offer fast, flexible financing to cover unexpected tax costs or help smooth your cash flow ahead of the limited company tax return deadline (especially if your revenue is seasonal).

Whether it’s for Corporation Tax, VAT, or other expenses, we can help you meet your obligations without the pressure of large lump sum payments. 

• Apply online and, if approved, get funding within hours.
• You can get a short-term loan from £1,000 to £1,000,000 with no collateral required, to use for any purpose your business needs. 

When you apply, you’ll typically get a decision on your application within 24 hours and could receive funds as soon as the next business day. So if you need to pay your tax, but don’t want to eat into your cash flow, an iwoca Flexi-Loan could be exactly what you need. 

Find out how iwoca’s business loans can help you meet your tax liabilities – with no hidden fees, no long waits, and no hassle.