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What is a Corporation Tax Self Assessment? 

  • 3 min read
  • Last updated 10 Oct 2024

Wondering what exactly a Corporation Tax Self Assessment (CTSA) is? Don’t worry, we’re here to make it easy for you! 

We’re going to break down Self Assessment, company tax returns, and everything you need to keep your business on the right side of HMRC. 

So, let’s dive in! 

What is a Self Assessment? 

A Self Assessment is how you tell HMRC about your untaxed income. It’s your responsibility to spill the beans on all your earnings and expenses so you can pay the right amount of tax on your profits. 

Here’s what a Corporation Tax Self Assessment usually includes:

  • A CT600 form (for corporation tax)
  • Your company accounts for the financial year
  • Company finances (the breakdown of the figures in your return)
  • Any additional documents needed

Getting your company tax return right is important. It ensures you pay the correct amount of corporation tax and helps you steer clear of potential penalties from HMRC.

What do limited companies pay tax on?

The main tax limited companies should be aware of is corporation tax, which is based on your business’s annual profits. The rate you’ll pay depends on how much profit you make.

Corporation tax is due 9 months and 1 day after your accounting period ends. Here’s an example if your financial year ended on 31 May 2024. 

  • File annual accounts with Companies House by 28 February 2025
  • Pay or report corporation tax to HMRC by 1 March 2025
  • File your company tax return by 31 May 2025

What other taxes do limited companies pay? 

In addition to corporation tax, your limited company may also need to pay:

  • Value Added Tax (VAT) – a tax on the value added to goods and services.
  • National Insurance Contributions (NICs) – if your business has employees, you’ll need to pay NICs. 
  • Business rates – you’ll need to pay these if your business is run from a commercial property, like an office.
  • Capital Gains Tax (CGT) – ​​a tax you pay when you sell or dispose of an asset for a profit. 
  • Income Tax – if you earn a salary over £12,570, you’ll need to pay income tax even if you’re a company director.
  • Dividends Tax – you’ll need to pay it if you take dividends as part of your income.

How to pay Self Assessment tax 

You can pay your corporation tax bill online, in full or in instalments, through your HMRC tax account

If you’re a company director and you need to file a personal tax return, you’ll need to register for Self Assessment. This can be done online through the HMRC website or by completing a paper form. For more information, click here

How to find my Self Assessment login 

To file updates like your annual company tax return, you or your accountant will need your Companies House authentication code. If you’ve forgotten it or need a reminder, don’t worry, here’s how to get a new one:  

1. Log in to Companies House – head to the Companies House website and sign in via their web filing service. If you don’t have an account already, you can create one here.

2. Find the authentication code section – once you’re logged in, find the section for managing your authentication code. This will be under your account settings or company security.

3. Request a new code – follow the on-screen instructions to request a new authentication code.

4. Wait for your code  Companies House will send your code to your registered address or email. It should arrive within a few days. If you already have one, they’ll send you a reminder.

What happens if I pay it late?

If your payment is late or not enough, HMRC will add interest to what you owe. 

HMRC’s late payment rates are linked to the Bank of England. So, you’ll pay a set base rate plus 2.5%. If your bill is already late, pay it sooner rather than later to avoid extra penalties.

And if you’re having trouble paying, don’t worry – reach out to HMRC directly. They might be able to set up a payment plan to help. You can call them on 0300-200-3822.

Need a helping hand? 

Unsure about your corporation tax? No worries, we’ve got you covered! We can match you with a qualified accountant who will review your tax situation and provide expert advice to help you navigate your liability. Contact us today

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