Log in

Corporation Tax

Your CT600, now HMRC's free filing service has closed

HMRC's free online service for company accounts and tax returns closed on 31 March 2026. Work out your pay and file dates below, then see your options for filing.

Try Finn free for 14 daysWork out what you'll owe

How do I file a CT600 now HMRC's free service has closed?

HMRC's free online service for filing company accounts and tax returns closed on 31 March 2026. Since 1 April 2026 you file the Company Tax Return with commercial software. You still pay Corporation Tax 9 months and 1 day after your accounting period ends, and file the return within 12 months.

Your Corporation Tax dates

Pay by

1 January 2027

83 days left

File by

31 March 2027

172 days left

Companies House accounts deadline: 31 December 2026. The Companies House register shows the exact date for a real company: look it up here.

What changed

What changed on 31 March 2026

HMRC used to offer a free online service for small companies to file both their annual accounts and their Company Tax Return in one place. That service closed on 31 March 2026. From 1 April 2026, you should use commercial software to file annual accounts and Company Tax Returns with HMRC.

This mainly affects directors who used to prepare and file their own Corporation Tax return through HMRC's website without paying for software or an accountant. If that was you, you now need a route that involves commercial software somewhere in the chain, even if you're still doing the filing yourself.

Your options

Your options now

There are three routes, and none of them require you to change how the company runs day to day.

  1. 1. Buy commercial CT software and file it yourself

    HMRC publishes a list of commercial software suppliers for Corporation Tax. You do the accounting and the filing, the software handles the iXBRL and the submission.

  2. 2. Have an accountant file for you

    Your accountant prepares the accounts, the computation and the CT600, and files with software they already hold a licence for.

  3. 3. Let Finn prepare the figures, you or your accountant file

    Finn prepares the Corporation Tax computation, the CT600 figures and the accounts in iXBRL, from the books it's already kept as you went. Finn does not file the CT600: you, or your accountant, file it with the software of your choice.

The form

What goes into a CT600

The CT600 covers your company details and the accounting period it's for, then your turnover, your profit, any capital allowances you're claiming, and the Corporation Tax due once those are worked through. It's filed alongside two supporting documents: your annual accounts and a Corporation Tax computation, both in a technical format called iXBRL that lets HMRC and Companies House read the figures directly rather than a scanned PDF.

None of this needs to be filled in from scratch each year. It's built from the same bookkeeping you already do: your income, your expenses, and any assets the company bought that qualify for capital allowances.

Deadlines

Deadlines and what late costs

Corporation Tax is paid 9 months and 1 day after your accounting period ends. Companies with profits over £1,500,000 pay in quarterly instalments instead, on an earlier schedule. The Company Tax Return itself is due later: 12 months after the accounting period ends.

How latePenalty
1 day£200
3 monthsAnother £200
6 monthsHMRC estimates your bill and adds 10% of the unpaid tax
12 monthsA further 10% of the unpaid tax

File late three times in a row and the £200 flat penalties rise to £1,000 each. Late payment interest currently runs at 7.75% (the Bank of England base rate plus 4 percentage points), from 9 January 2026.

First year

Two returns in your first year?

A Corporation Tax accounting period can never be longer than 12 months. Most companies' first accounts period runs longer than that, which means the first year splits into two Corporation Tax periods and two Company Tax Returns, both due on the same date. See company deadlines for a worked example with real dates.

Paying

How to pay Corporation Tax

Pay HMRC online, by bank transfer or by Direct Debit, using the payment reference HMRC gives you. Payment is due before the return itself, so you can pay the amount you expect to owe even before the CT600 is filed. See gov.uk for how to pay.

Where Finn helps

Finn prepares the figures, you or your accountant file

Finn keeps the books as you go, then turns them into the Corporation Tax computation and CT600 figures when your year ends.

Try Finn free for 14 days
  • Keeps the books up to date as you go
  • Prepares the Corporation Tax computation and CT600 figures
  • Prepares annual accounts (FRS 105) for review and filing to Companies House
  • Tracks your Corporation Tax payment and filing dates
  • Answers 'how much Corporation Tax will I owe?' from your own books

Questions

CT600 filing, answered

What is a CT600?

The CT600 is the Company Tax Return: the form a limited company files with HMRC to report its profit and work out its Corporation Tax. It's filed alongside the company's annual accounts and a Corporation Tax computation, in iXBRL format.

Can I still file my own Corporation Tax return for free?

HMRC's free online filing service for company accounts and tax returns closed on 31 March 2026. Since 1 April 2026, you file the Company Tax Return using commercial software, whether that's software you buy yourself, an accountant's, or Finn preparing the figures for you or your accountant to file.

How do I file a CT600 without HMRC's free software?

You need commercial software recognised for Corporation Tax filing. HMRC publishes a list of suppliers, or an accountant can file on your behalf with software they already use, or Finn can prepare the figures, computation and accounts for you or your accountant to file with software of your choice.

How do I pay Corporation Tax?

Pay HMRC online, by bank transfer or by Direct Debit, using the payment reference HMRC gives you. Payment is due 9 months and 1 day after your accounting period ends, before the Company Tax Return itself is due.

What's the Corporation Tax payment deadline?

9 months and 1 day after your accounting period ends. Companies with profits over £1,500,000 pay in quarterly instalments instead, on an earlier schedule.

What happens if I file my CT600 late?

£200 as soon as the deadline passes, another £200 if it's more than 3 months late, then HMRC estimates your bill and adds 10% of the unpaid tax at 6 months, and a further 10% at 12 months. Three late filings in a row turns the £200 flat penalties into £1,000 each.

Can I do my own Corporation Tax return?

Yes. You'll need commercial software to file since HMRC's free service closed, and you're responsible for getting the figures right. Many directors choose an accountant, or Finn, to prepare the computation and accounts instead, then file themselves or have their accountant file.

Will I file two Company Tax Returns in my first year?

Often, yes. A company's first accounts period is usually longer than 12 months, and a Corporation Tax accounting period can never exceed 12 months, so it splits into two returns. Both are due on the same date. Search your company number on our company deadlines page to see your own dates.

Sources, checked on

General guidance, not advice for your situation. Rules change: always check the GOV.UK page before you act.

Let Finn get your figures ready

Finn prepares your Corporation Tax computation, CT600 figures and accounts, so filing is a formality, not a scramble.

Try Finn free for 14 daysCheck your company's dates