How to Add Self Assessment to Your Government Gateway Account
How to Add Self Assessment to Your Government Gateway Account
Short answer: sign in to your HMRC business tax account, choose Get online access to a tax, duty or scheme, pick Self Assessment and enter your UTR. HMRC then posts you an activation code, which can take up to 10 days. Enter the code in your account and Self Assessment is added.
Just want to sign in? HMRC's sign-in page is on GOV.UK: HMRC online services: sign in or set up an account. If you use GOV.UK One Login and want to file through software, see Government Gateway sign-in for Self Assessment software.
What you need before you start
- Your sign-in details. A Government Gateway user ID (up to 12 characters) and password, or GOV.UK One Login (an email address and password).
- Your UTR. The 10-digit Unique Taxpayer Reference HMRC gives you when you register for Self Assessment. Find a lost UTR on GOV.UK.
- Your current address. The activation code is sent by post to the address HMRC holds for you.
If you haven't registered for Self Assessment yet, do that first: register for Self Assessment on GOV.UK. Register by 5 October after the end of the tax year you need to file for.
How to add Self Assessment to your account
- Sign in to your HMRC business tax account. Use the same Government Gateway user ID each time: HMRC says you must only use one user ID for your business taxes.
- On the home page choose Get online access to a tax, duty or scheme. You can also open Manage account in the top menu and choose Add a tax, duty or scheme to your account.
- Select Self Assessment and enter your UTR when asked.
- Wait for the activation code. HMRC posts it to you. Its guidance says this can take up to 10 days.
- Activate. Sign in again, enter the code, and Self Assessment appears in your account.
The steps and menu names come from HMRC's guide, How to use your HMRC business tax account.
Other taxes you can add the same way
| Tax | Who it is for | What HMRC asks for |
|---|---|---|
| Self Assessment | Self-employed people, landlords, and anyone with income HMRC doesn't tax automatically | Your UTR |
| VAT | VAT-registered businesses | Your VAT registration number and details from your registration |
| PAYE for employers | Businesses with employees | Your employer PAYE reference and Accounts Office reference |
| Corporation Tax | Limited companies | Your company's UTR |
If you use GOV.UK One Login
New HMRC customers have signed up with GOV.UK One Login since 9 February 2026, and One Login will replace Government Gateway over time. You can still see and manage Self Assessment in your HMRC account. To file through commercial software, though, GOV.UK says One Login users need a separate Government Gateway user ID and password, which you create from your sign-in details. Our page on Government Gateway sign-in for software shows the steps.
Common problems
- The activation code hasn't arrived. Allow the 10 days, and check that HMRC has your current address. If it still hasn't come, sign in and ask for a new one.
- You've lost your user ID or password. You can recover or reset them when you try to sign in. HMRC's sign-in help explains how.
- Your account is locked. Too many wrong attempts lock it for 2 hours. HMRC's helpdesk can't unlock it sooner.
- You've got a new phone. Sign in with your user ID and password, then choose "You can get help" when you're asked for an access code.
Once Self Assessment is on your account
You can file your tax return through HMRC's own service or through HMRC-recognised software. With DTax Filer you prepare the return first, check the tax calculation, and only enter your UTR and Government Gateway details when you submit.
See the plans and prices, or read about the Self Assessment deadlines for 2025–26.
Frequently asked questions
How long does the HMRC activation code take to arrive?
HMRC's business tax account guidance says it can take up to 10 days to arrive in the post. It goes to the address HMRC holds for you, so check that is up to date.
Do I have to add Self Assessment before I can file a tax return?
Yes. HMRC has to link your sign-in details to your Self Assessment record before a return can be filed with them, whether you use HMRC's service or software. You can still prepare your return in DTax Filer while you wait for the code.
Is a Government Gateway user ID the same as a UTR?
No. The user ID (up to 12 characters) is how you sign in. The UTR (10 digits) identifies your tax record. You need both to file a Self Assessment return through software.
Can I add Self Assessment if I sign in with GOV.UK One Login?
Yes, you can use Self Assessment in your HMRC account with One Login. To submit a return through software you also need Government Gateway details for software, which you create from your sign-in details.
Can I have more than one Government Gateway user ID?
HMRC says you must use only one user ID for your business taxes: the one you used to register your first tax. Adding each tax to that one account keeps everything in one place.