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How to switch on Corporation Tax in your Government Gateway (and enter the activation code)

Updated 15 July 2026
The short answer

If you can sign in but Corporation Tax is nowhere in your account, it just has not been switched on yet. Sign in to your company's business tax account, choose "Services you can add", pick Corporation Tax, and enter your company's 10-digit tax reference (the UTR). HMRC then posts an activation code to your company's registered office, usually within 10 days. When the letter arrives, sign back in and type the code in, and you must do that within 28 days of the date on the letter. If you already have the letter in your hand, skip ahead and enter the code now.

Official source. This guide is a plain-English summary of official GOV.UK guidance, not advice. The authoritative source is Add Corporation Tax services to your business tax account on gov.uk. Always rely on that over our summary.

What does "enrolling" for Corporation Tax actually mean?

HMRC's online account works a bit like a phone with no apps installed. Signing in gets you through the front door, but each tax is a separate service you have to add before you can use it. Adding Corporation Tax to your account is what HMRC calls enrolling. Until it is done, your account simply does not hold your company's Corporation Tax, so nothing to do with your Company Tax Return will work, even though your sign-in is perfectly fine.

This is the single most-missed setup step, and it is not your fault. Nothing tells you it exists until something refuses to work.

Why can't I see Corporation Tax in my account?

There are three common reasons, and none of them mean you have broken anything:

  • You are in your personal account, not a business one. The account you use for your own Self Assessment is separate from your company's business tax account, and Corporation Tax lives in the business one. If you only have a personal account, you can create a business tax account on gov.uk in about 5 minutes, then add Corporation Tax to it.
  • Corporation Tax was never added. The account exists, but nobody has done the "add a tax" step yet. The walkthrough below fixes that.
  • Someone else already holds it. Corporation Tax can only be switched on in one Government Gateway account at a time. If an old accountant or a former director enrolled it in theirs, it stays there until HMRC moves it, so your own perfectly good sign-in gets turned away. Ring the Corporation Tax helpline on 0300 200 3410 and ask them to move it to your account.

How do I add Corporation Tax to my account?

Have your company's 10-digit tax reference (the UTR) ready. It is on letters HMRC has sent your company. You will also be asked for your company registration number, the date the business started, and the date your first accounts are made up to.

One thing to check first: HMRC will post the activation code to your company's registered office, the official address held at Companies House. Make sure that address is right, and that someone there will actually open the post.

Then:

  1. Sign in to your company's business tax account at gov.uk with your Government Gateway user ID and password.
  2. Choose "Services you can add" from the menu (on some screens it is worded as adding a tax to your account).
  3. Find Corporation Tax in the list and choose "Enrol for service".
  4. Enter your company's 10-digit UTR and the other details when asked.
  5. That is it for now. HMRC posts the activation code to your registered office. You cannot speed this bit up online, it comes on paper.

What happens with the activation code letter?

The letter usually arrives within 10 days (21 days if you live abroad). It goes to the registered office, not necessarily your home. For lots of small companies that is their accountant's address, so the letter can land somewhere you never see. If that is your setup, ask your accountant to watch the post for you.

While you wait, there is nothing more you need to do. When the letter arrives, you sign back in and enter the code, as described below.

I have the letter. How do I enter the code?

  1. Sign in to the same business tax account you used to enrol. Same user ID, same password.
  2. You will see Corporation Tax waiting with a prompt to activate it.
  3. Type in the activation code exactly as it appears on the letter.
  4. Do this within 28 days of the date printed on the letter. After that the code expires and you have to request a new one, which means another wait for the post.

Once the code is accepted, Corporation Tax appears as a live service in your account, listed against your company's name and UTR. That is what "done" looks like: you sign in, and Corporation Tax is simply there. Filing software can now connect and send your return.

How long does the whole thing take?

  • Adding the tax online: a few minutes, once you have your UTR to hand.
  • Waiting for the code: usually up to 10 days by post, 21 if you are abroad.
  • Entering the code: under a minute.

So from scratch, allow a week or two end to end. If your filing deadline is inside that window, start the enrolment today, because the postal wait is the one part you cannot compress and the deadline does not wait for the post.

Common questions

My activation code never arrived. What do I do?

First check the registered office address, because that is where HMRC sends it, and for many companies that is an accountant's address rather than their own. If the address is right and the letter still has not turned up after 10 days or so, you can request a new code, or ring the Corporation Tax helpline on 0300 200 3410. The same goes for an expired code: request a new one, no harm done.

I can already sign in for my Self Assessment. Why can't I see Corporation Tax?

Because that is your personal account, and Corporation Tax lives in a separate business tax account for the company. Having one does not give you the other. Create a business tax account (it takes about 5 minutes), then add Corporation Tax to it.

My old accountant set everything up. Where is my Corporation Tax?

Very likely still enrolled in their Government Gateway account. Corporation Tax can only sit in one account at a time, so it stays with them until HMRC moves it. Ring 0300 200 3410 and ask HMRC to move the Corporation Tax enrolment to your own account.

Where do I find my company's UTR?

It is the 10-digit number on letters HMRC has sent your company, including the one that arrived soon after the company was formed. If you cannot find it anywhere, our guide on finding your company UTR shows you how to get a copy.

I used to file with HMRC's free service. Do I still need to do all this?

HMRC's free online filing service has closed, so returns now go in through commercial software. Your company still needs Corporation Tax switched on in its business tax account, so yes, this step still matters.

Stuck at exactly this step? We check it for you

SimpleReturns files Company Tax Returns for small companies, and the step where you connect your company has a built-in rescue wizard for precisely this problem, with a quick "check your sign-in first" step and a before-you-start checklist, so a missing enrolment gets caught early instead of at the worst moment. It is free to start, no card needed; filing costs £99, flat, per submission.

Start your return

And if your situation is knottier, say the enrolment is trapped in a departed accountant's account and the deadline is tomorrow, ringing HMRC on 0300 200 3410 is honestly the fastest fix, then come back.

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.