How to register for Self Assessment

In this guide, we’ll explain how and when to register for Self Assessment, and how the registration process might vary depending on your circumstances.

When to register for Self Assessment

You must register for Self Assessment with HMRC if you have to send a tax return and you did not send one last year. If you’re unsure about whether or not you have to file, our dedicated guide contains more information about who has to send a tax return.

The deadline for registering for Self Assessment is the 5th October that follows the end of the tax year that the Self Assessment tax return you’re filing relates to. For example, if the tax return relates to the tax year starting 6th April 2021 and ending 5th April 2022, you should register for Self Assessment by 5th October 2022. If you don’t register by the appropriate deadline, you could be fined. 

Please note that if you registered for Self Assessment and filed a tax return last year, you don’t need to register again.

How to register for Self Assessment

Registering if you’re self-employed

If you’re self-employed, here’s what you need to do if you’re required to register for Self Assessment. HMRC provides more information about how to do this on its website.

If you already have a business tax account, you can register by signing in to this account and adding Self Assessment to your list of services. You’ll need a Government Gateway user ID and password in order to to sign in to your business tax account.

If you don’t have a business tax account or a Government Gateway user ID, select ‘Create sign in details’ link on the login page and follow the instructions.

You should receive a letter from HMRC with your Unique Taxpayer Reference (UTR) number within 10 working days (21 days if you live abroad). You should also receive a separate letter within seven working days with an activation code for your business tax account. You can retrieve a lost UTR number or get a new activation code from HMRC if you lose either of them after they arrive.

Once you’ve received your UTR number and activation code, you can log in to, and activate, your business tax account. Once you’ve done this, you should be able to add Self Assessment to your list of services and file your tax return.

Registering if you’re not self-employed

If you’re not self-employed, here’s what you need to do if you’re required to register for Self Assessment. HMRC provides more information about how to do this on its website. 

Those who are not self-employed and are required to register for Self Assessment need to do so using form SA1. You can complete the form online (you’ll need an account with HMRC to log in) or print it out and post it to HMRC.

Even if you print and post your form, you still need to create an online account with HMRC in order to register. Once you’ve done this, you should then receive a letter from HMRC within seven working days (21 days if you live abroad) with an activation code for your account. Once you’ve received this, you can log in to and activate your online account.

Once you’ve submitted form SA1, you should receive a letter with your Unique Taxpayer Reference (UTR) number within 10 working days (21 days if you live abroad). You can retrieve a lost UTR number from HMRC if you lose it after it arrives.

Once you’ve activated your account, you should be able to log in, add Self Assessment to your list of services and file your tax return (you’ll need your UTR number in order to do this).

If you’re a partner in a partnership

Partners in partnerships are required to register for Self Assessment using form SA401. HMRC provides more information about how to do this on its website.

You’ll need your partnership’s UTR number in order to complete form SA401. You can retrieve this number from HMRC if you’ve lost it. 

You can complete form SA401 online or print it out and post it to HMRC.

If you’re the ‘nominated partner’ of the partnership, remember that you are also responsible for registering your partnership for Self Assessment (in addition to registering yourself as an individual).

Filing your Self Assessment with FreeAgent

If you’re a sole trader or limited company director and you’re looking for a simple way to complete and file your Self Assessment tax return, our online accounting software might be the answer.

FreeAgent provides you with a clear overview of your tax position and helps you see all your liabilities build up over time, so you’ll know what you owe and when. Take a closer look at Self Assessment in FreeAgent and start your 30-day free trial today.

Disclaimer: The content included in this guide is based on our understanding of tax law at the time of publication. It may be subject to change and may not be applicable to your circumstances, so should not be relied upon. You are responsible for complying with tax law and should seek independent advice if you require further information about the content included in this guide. If you don't have an accountant, take a look at our directory to find a FreeAgent Practice Partner based in your local area.

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