SimpleReturns

How do I file my Company Tax Return?

Updated 27 June 2026
The short answer

Filing your Company Tax Return takes five steps: prepare your accounts, work out the tax behind them, fill in the CT600 form (your profit and the tax you owe), send it all to HMRC online, and pay the tax. The accounts and the working have to go in a digital format HMRC reads automatically, so you either use filing software yourself or let a tool like ours build and send the whole thing for £99.

What does "file my Company Tax Return" actually mean?

It means sending HMRC three things together, once a year:

  • Your accounts, a summary of the money your company took in and spent over the year.
  • The working, a short set of sums that shows how you got from your accounts to your tax figure.
  • The CT600 form, where you put your profit and the Corporation Tax you owe.

Together those three are your Company Tax Return. The form on its own is not enough, all three travel to HMRC as one return.

What are the steps, in order?

Here is the whole job, start to finish. The same five steps apply whoever does them.

  1. Prepare your accounts. Add up the money in and the money out over your company's year, and turn it into a proper set of accounts.
  2. Work out the tax. Take your accounts, take off the costs the rules allow, and work out your profit and the Corporation Tax on it. This part is "the working".
  3. Fill in the CT600. Put your profit and your tax figure into the CT600 form.
  4. Send it to HMRC online. The accounts and the working have to go in a digital format HMRC reads automatically, so this step needs filing software.
  5. Pay the tax. You pay your Corporation Tax to HMRC by their deadline. The tax is separate from any fee you pay for filing.

If that sounds like a lot, that is the honest picture. We do steps 1 to 4 for you from your bank figures, and tell you exactly what to pay and when for step 5.

Do I have to file one at all?

If your company is active, almost certainly yes. HMRC sends you a letter called a "notice to deliver a Company Tax Return", usually once your company starts trading, and that letter is your cue to file. You still send a return even if your company made a loss, earned nothing, or owes no tax.

How do I send it to HMRC?

This is the step that has changed, and it catches people out. There used to be a free government website where small companies filed their accounts and tax return in one place. That free service has closed. So to file yourself today, you use commercial filing software instead.

Filing software matters because the accounts and the working can't go to HMRC as a normal document or a PDF. They have to be in a special digital format HMRC reads automatically, with each figure tagged so its computers can pick it out. You don't tag anything by hand, the software does it, but you do need software that produces it. Some software is free or low-cost for a simple small company.

Can I really do this myself?

Yes, you can. People file their own Company Tax Return every year. If your company is simple and you are confident with numbers, doing it yourself with filing software is a real option, and the cheapest in money.

The honest catch: the software hands you a blank form, not the answers. You still work out your own profit, decide which figure goes in which box, get the tax right, and produce the tagged digital file. If you are sure of all that, go for it. If you are not, it is slow and easy to get wrong, and a wrong figure on a tax return is not a small thing.

When is it due?

There are two different dates, and the one for paying comes first:

  • Pay your Corporation Tax: usually 9 months and 1 day after your accounting year ends.
  • Send the CT600: 12 months after your accounting year ends.

So you pay the tax before you file the return. If your year ends on 31 March, you would normally pay by the following 1 January and file by the following 31 March. Miss the filing date and HMRC charges a penalty that starts at £200, even if you owe no tax, with more added the longer it is left.

What about my accounts at Companies House?

Filing your tax return is not the only yearly job. Your accounts also go to Companies House, a different government body, for the public record. That is a separate filing, usually due 9 months after your year-end. You can do the two jobs together or one at a time.

So most small companies have two filings to two places each year: the Company Tax Return to HMRC, and the accounts to Companies House. They cover the same year and share a lot of the same numbers, which is why people mix them up. We send both for you, in one go.

How SimpleReturns handles it

Connect your bank or upload a statement, and we do the work in your place: we add up your year's money in and out, work out your profit and your Corporation Tax, build your CT600, your accounts and the working behind them, and produce the tagged digital file HMRC needs. You check every figure, then we send the accounts to Companies House and the CT600 to HMRC, for £99, once, no subscription. You pay the Corporation Tax itself straight to HMRC, and we show you the amount and the deadline.

Common questions

What are the steps to file a Company Tax Return?

Prepare your accounts, work out your profit and the tax, fill in the CT600 form, send all three to HMRC online in the digital format it needs, and pay the tax by the deadline.

Can I file my Company Tax Return myself for free?

You can file it yourself, and some filing software is free or low-cost for a simple small company. The old free government filing website has closed, so you now need that software. Either way you work out every figure and produce the tagged digital file yourself, so the saving is in money, not effort.

Do I need special software to file?

Yes, if you file yourself. The accounts and the working have to go to HMRC in a digital format its computers read automatically, and only filing software produces that. You never tag anything by hand.

When do I have to file and pay?

File the return within 12 months of your accounting year-end. Pay the tax earlier, usually 9 months and 1 day after year-end, so you pay before you file.

Is filing my tax return the same as filing my accounts at Companies House?

No. The Company Tax Return goes to HMRC. Your accounts also go to Companies House, a separate body, usually 9 months after year-end. They are two jobs to two places, sharing the same figures.

What happens if I file late?

HMRC charges a penalty that starts at £200, and it applies even if your company owes no tax, with more added the longer you leave it. So the deadline matters whoever files.

Ready to do it the easy way?

You don't need to learn a single tax rule or touch a tagged file to file your return. Connect your bank, and we work out your figures, build your tax return and your accounts, show you everything to check, and send both to the right place, for £99, once, no subscription.

Start your return →

Or, if your company is more complex, like a group, claims a specialist relief, or you want advice through the year, an accountant may be the better fit, and that is an honest call to make.

General guidance, not advice. This guide explains how the rules generally work for small UK limited companies. It isn't tax advice for your specific situation, if you're unsure, check with us or an accountant.