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How To Register For Self Assessment

Last reviewed: September 2025

Self Assessment can be confusing, especially if no one’s explained how it works. If you need to file a tax return, it’s your responsibility to tell HMRC. They won’t chase you for it – but they will issue penalties if you miss a deadline. However, registering for Self Assessment doesn’t have to be difficult. With RIFT, it’s simpler than it sounds.

This guide will explain how to enrol for Self Assessment in the UK, who needs to do it, what information you’ll need and how RIFT can help you every step of the way.

What is Self-Assessment and who need to register for it?

Self Assessment is how you tell HMRC about your income if it’s not taxed automatically. It’s most commonly used by people who are self-employed or have additional income outside of PAYE.

If you need to file a Self Assessment tax return, you must first register with HMRC, usually by 5th October following the end of the tax year.

You’ll typically need to register if you:

Are self-employed or a sole trader
Work in construction or work in construction under the CIS scheme (Construction Industry Scheme)
Earn money from a side hustle, freelance or contract work
Rent out property or earn income from abroad
Receive untaxed income or savings interest

There are grey areas too. Some people register and file even when they don’t have to, while others miss the deadline and end up facing penalties. If you’re not sure, it’s best to check before you act.

Self Employed Tax Returns Explained

Do I need to file a tax return?

If you’re self-employed, earn untaxed income, or work through CIS, chances are you need to file a Self Assessment tax return. But it’s not always black and white. You might need to file if:

You’ve earned over £1,000 from a side hustle or freelance work
You’ve claimed work expenses and want to claim a tax refund
You receive rental income or dividends

How to enrol for Self-Assessment

If you’ve never filed a tax return before, you’ll need to register with HMRC first. Here’s how to enrol for Self Assessment in the UK, step by step.

1. Tell HMRC you need to file

Go to HMRC’s website and let them know you need to complete a Self Assessment tax return. This is usually done online, but if you can’t use the digital service, you can register by post using form SA1.

2. Register for Self Assessment

If you’re self-employed, use the online form for sole traders. Others, like CIS workers or those with rental income, can use the standard Self Assessment registration.

Online — Visit gov.uk/register-for-self-assessment.
By post — Download and complete form SA1.

3. Get your UTR number

Once registered, HMRC will post your 10-digit Unique Taxpayer Reference (UTR). This usually takes around 10 working days. You’ll need this number whenever you file a return.

4. Set up your Government Gateway account

You’ll need this to access HMRC’s online services. During setup, HMRC will send an activation code by post. It can take 7–10 days to arrive.

It’s not always smooth sailing, but RIFT can guide you through the whole process if you get stuck.

What you'll need to register

Before you start your Self Assessment registration, it helps to have a few key details ready. Here’s what you’ll need:

National Insurance number
Full name and date of birth
Contact details, including your address, email and phone number
Employment details, including your job type or business name
The date you started self-employment

Don’t worry if you don’t have everything to hand. RIFT can still help you get started and guide you through what’s needed, even if you’re missing a few bits.

Deadlines, penalties and what happens if you don't register

Missing a Self Assessment deadline can be costly. HMRC won’t remind you to register but they will issue penalties if you’re late. Key deadlines include:

5 October — Deadline to register for Self Assessment.
31 January — Deadline to file your return and pay any tax owed.
31 July — Second payment on account deadline.

What happens if you miss them:

£100 fine if your return is up to 3 months late
Daily penalties of £10 per day after 3 months (up to £900)
Interest and surcharges on unpaid tax

Even if you’ve missed a deadline, you might still be owed a refund. RIFT can help you backdate claims and check if you qualify.

HMRC penalties

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I'm not self-employed, but I still have to register for Self Assessment. What do I do?

The way you register for Self Assessment is generally the same even if you aren't self-employed. All the same basic rules apply, including the 5th of October deadline. If you've sent in tax returns before, you can use your existing Unique Taxpayer Reference number and log into your online account to file your returns. If you don't have an account or UTR, you need to apply for them on the HMRC site. Again, you're probably looking at a few weeks waiting time to get set up, so make sure you register early.

I'm in a business partnership. How do I register for Self Assessment?

When you're in a partnership, you've got 2 Self Assessment registrations to make – one for you and one for the business itself. One of the partners has to be in charge of the business' tax records (the “nominated partner”). If that's you, it means you have to register the partnership for Self Assessment and deal with all its tax paperwork. Like a person, the partnership will get a Unique Taxpayer Reference number to use when filing its tax returns.

As a partner, you'll also have to register for the system yourself. Again, though, the basic rules and deadlines are the same. If your business is a Limited Liability Partnership, of if the Parter you're registering is itself a company, then special rules apply. Talk to RIFT to make sure everything's done properly.

What is a UTR number and why do I need it?

Your UTR (Unique Taxpayer Reference) is a 10-digit number that HMRC uses to identify you for tax purposes. It’s essential for filing a Self Assessment tax return in the UK. You can’t submit one without it.

You’ll receive your UTR by post after registering for Self Assessment. If you’ve lost it, don’t panic, RIFT can help you track it down or request a replacement.

What you can claim back on your tax return

Most people miss out on money they’re owed simply because they don’t know what they can claim. If you’re working for yourself or through CIS, you could be due a tax refund for everyday work expenses. These are some of the most common things you can claim:

Tools and equipment needed for your job
Protective clothing and uniforms
Travel costs to temporary sites
Home office expenses if you work from home
Phone bills, stationery and admin costs

Can I get help registering for Self Assessment?

Of course! RIFT are the UK's leading tax experts, and can handle the whole process for you. Take a look at our tax return calculator to check if you need to register. If you do, leave everything to us. We'll take the taxman's weight off your shoulders so you can get back to business.

Why let RIFT handle your Self-Assessment?

Filing a Self Assessment tax return doesn’t have to be a solo job. With RIFT, you get expert support from start to finish and more money back in your pocket.

We’ve been doing this for over 20 years and we’ve claimed back more than £350 million for people like you. Whether it’s your first return or your fifth, we’ll make sure you get it right.

Start your return with RIFT today by getting in touch.

Contact RIFT

Frequently asked questions

How do I enrol for Self-Assessment with HMRC?

You can register online through the HMRC website or by post using form SA1. Once you’ve registered, you’ll receive a UTR number and can set up your Government Gateway account to manage your tax return online.

What is UTR number and how do I get one?

Your UTR is a 10-digit number that HMRC uses to identify you for tax purposes. You’ll receive it by post after registering for Self Assessment. If you lose it, you can request a copy or ask RIFT to help recover it.

What if I miss the Self-Assessment deadline?

If you miss the registration or filing deadlines, HMRC can issue fines and charge interest on any unpaid tax. But you may still be able to file late and claim a refund. RIFT can help you minimise penalties and recover what you’re owed.

Do I need to file a tax return every year?

Once you’re registered for Self Assessment, you’ll need to file a return every year until HMRC tells you otherwise. Even if your income hasn’t changed, it’s your responsibility to submit on time.

What documents do I need to register?

You’ll need your National Insurance number, personal details, employment or business info, and the date you started earning untaxed income. If you’re unsure, RIFT can help you fill in the gaps.

Can RIFT help me if I'm already registered?

If you’re already set up with HMRC, RIFT can handle your tax return, speak to HMRC on your behalf and make sure you claim everything you’re entitled to.

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How To Register For Self Assessment​