How to register for Self Assessment

There are a number of reasons why a taxpayer needs to complete and register for a Self-Assessment tax return. If you have recently gone self-employed, started earning rental income, or have any other untaxed income, you will need to register for Self Assessment with HMRC. This is how HMRC collects income tax from people whose tax is not automatically deducted through PAYE.

Registering for Self Assessment for the first time can feel daunting, but the process is straightforward if you follow the right steps. The key things to know upfront are:

• The registration deadline is 5 October, following the end of the tax year in which you became liable
• You register online through the Government Gateway using either the CWF1 form (if self-employed) or the SA1 form (for other income)
• After registering, HMRC will post you a UTR number within 10 to 15 working days
• Your first tax return must be filed and paid by 31 January following the end of the tax year

This guide walks you through exactly how to register for self-assessment, step by step.

Who needs to submit a tax return?

One of the most common questions we receive is: Do I need to register for Self Assessment? HMRC’s rule is simple: if you have income that has not been taxed at source (through PAYE) you almost certainly need to register. This includes,

• Individuals earned more than £1,000 from self-employment;
• Taxpayers who had £2,500 or more in untaxed income;
• Those with savings or investment income of £10,000 or more before tax;
• Taxpayers who made profits from selling things like shares, a second home or other chargeable assets and need to pay Capital Gains Tax;
• Company directors – unless it was for a non-profit organisation (such as a charity) and you didn’t get any pay or benefits, like a company car;
• Taxpayers whose income (or that of their partner’s) was over £50,000 and one spouse/partner claimed Child Benefit;
• Individuals who had income from abroad that they needed to pay tax on;
• Taxpayers who lived abroad and had a UK income;
• An individual with an income over £100,000.

Which form do I need to register for Self Assessment?

Before you start the registration process, you need to know which route applies to you, using the wrong form causes delays:

CWF1 form – for self-employed sole traders and freelancers. If you are starting or have started working for yourself, use the CWF1 form. This registers you for Self Assessment and for Class 2 and Class 4 National Insurance contributions simultaneously. Do not use the SA1 form if you are self-employed, which registers you for Self Assessment but misses the National Insurance side, which creates gaps in your State Pension record.

SA1 form – for everyone else. Use the SA1 form if you need Self Assessment for any reason other than self-employment, including:

• Rental income as a landlord
• Income from overseas
• Savings or investment income above the threshold
• Company directors
• Income over £100,000

SA400 and SA401 – for partnerships. If you are registering a business partnership, use SA400 for the partnership itself and SA401 for each individual partner.

How to register for Self Assessment online – step by step

The following steps cover the CWF1 route for self-employed individuals. The SA1 route follows the same Government Gateway process but asks different questions at Step 4.

Step 1: Check whether you already have a Government Gateway account

Go to https://www.gov.uk/log-in-file-self-assessment-tax-return. You will see a screen asking whether you have used HMRC online services before.

Scroll down and press Sign in.

You will get to the screen below.

• If you already have a Government Gateway ID from another HMRC service (e.g. checking your tax code, or a previous employer’s PAYE): use those same credentials do not create a new account.
• If you have never used HMRC online services, click “Create sign-in details” and proceed.

Step 2: Create your Government Gateway account

You will be asked to enter your email address and create a password. HMRC will send a verification code to your email. Enter it to confirm your address.

You will then be given a Government Gateway user ID, a 12-digit number. Write this down immediately and store it somewhere safe. You will need it every time you log in to HMRC services.

Step 3: Verify your identity

HMRC will ask you to verify your identity before proceeding. You will be offered several options:

• Using the HMRC app (fastest uses face ID or fingerprint on your phone)
• With your UK passport
• With your driving license
• By answering questions about your credit history (name, address history, and financial accounts)

Choose whichever method applies to you and follow the on-screen prompts. If none of the online options work, HMRC will offer to send a code by post (allow up to 7 days).

Step 4: Select “Self Assessment” and complete the CWF1 form

Once logged in, go to “Add a tax, duty or scheme”

and select “Self Assessment for individuals”.

Confirm you do not have UTR

Confirm you are an Individual or sole trader

You will then be asked why you need to register. Select “I am self-employed or a sole trader.”

The CWF1 form will then ask you for:

• Your National Insurance number (find it on your payslip, P60, or any HMRC letter)
• Your date of birth and home address
• Your business start date – the date you first started working for yourself, even if it was in a previous tax year
• Your business name – if you trade under your own name, this can just be your name
• A brief description of your work – e.g. “freelance graphic designer” or “plumbing and heating engineer.”
• Your phone number and email address

Make sure to complete all sections before submitting the form.

Step 5: Submit and write down your submission reference

Review all the information you have entered, then click Submit. HMRC will display a confirmation screen with a submission reference number.

Do not submit the form a second time if you are unsure whether it went through. Duplicate submissions create delays and can cause HMRC to open two separate records for you. If in doubt, call HMRC on 0300 200 3310 with your submission reference.

Step 6: Wait for your UTR number

After submitting, HMRC will post your Unique Taxpayer Reference (UTR) to your registered address. This is a 10-digit number that stays with you for life even if you stop self-employment and restart later.

Typical waiting times:

• UK address: 10–15 working days
• Overseas address: up to 21 working days
• Via the HMRC app: often faster – check the app after a few days

Do not lose your UTR. It appears on every letter HMRC sends you, labeled “UTR” or “Your tax reference.” You will need it to file your tax return and to contact HMRC about your Self Assessment.

Step 7: Activate your Self Assessment online account

When your UTR arrives by post, HMRC will also send (or prompt via the app) an activation code for your online Self Assessment account. Log back into your Government Gateway account and:

1. Go to “Self Assessment” in your account dashboard
2. Enter your UTR number when prompted
3. Enter the activation code
4. Your Self Assessment account is now active, and you can file your return online

Activation codes expire after 28 days. If yours expires before you use it, log in and request a new one. Do not re-register.

What happens after you register for Self Assessment?

Once your account is active, HMRC will expect you to file a Self Assessment tax return every year until you formally tell them you no longer need to. Even if you owe no tax, you must file a tax return or HMRC will issue automatic penalties for non-filing regardless.

As a self-employed sole trader, your return will consist of:

• SA100 – the main Self Assessment return
• SA103 – the supplementary self-employment pages where you declare business income and expenses

You will also make two types of National Insurance payments through your Self Assessment bill:

• Class 2 NICs – a flat weekly amount (£3.50 per week for 2025/26) that counts toward your State Pension
• Class 4 NICs – calculated as a percentage of your profits above the lower threshold

From April 2026, if your qualifying income exceeds £50,000, you will also need to comply with Making Tax Digital for Income Tax, submitting quarterly updates through HMRC-compatible software in addition to your annual return. See our MTD for Income Tax guide for full details.

Self-Assessment registration deadlines and penalties

Deadline	What it covers
5 October	Register for Self Assessment by this date in the year after you start trading
31 January	File your online Self Assessment return and pay any tax owed
31 July	Pay your second payment on account (if applicable)

Missing the 5 October registration deadline can result in a “failure to notify” penalty from HMRC. The penalty is calculated as a percentage of the tax owed and can be significant, particularly because HMRC can assess it going back to the date you first should have registered, not just the current year.

Missing the 31 January filing deadline results in:

• An automatic £100 fixed penalty from day one
• A further £10 per day penalty after 3 months (up to £900)
• Additional penalties at 6 months and 12 months
• Interest on any unpaid tax at the Bank of England base rate plus 2.5%

The message is clear: register early, file on time. If you have missed a deadline, a voluntary approach to HMRC will always result in lower penalties than waiting to be found.

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