How to Register for Self Assessment with HMRC in 2026 — Step by Step

If you have recently become self-employed, started earning rental income, received income that is not taxed at source, or had earnings above £150,000, you need to register for Self Assessment with HMRC. Missing the registration deadline results in automatic penalties that apply even if you owe no tax.

This step-by-step guide explains exactly who needs to register, when the deadline is, and precisely how to do it.

Who Needs to Register for Self Assessment?

You must register for Self Assessment if, in the 2025/26 tax year, any of the following applied to you:

You were self-employed as a sole trader and earned more than £1,000 from self-employment (before expenses). You earned rental income of more than £2,500 after allowable expenses, or more than £10,000 before expenses. You had income from abroad that needs to be reported in the UK. You received dividends from shares and you are a higher or additional rate taxpayer. Your total taxable income was over £150,000. You were a company director (unless the company was a non-profit and you received no pay). You claimed Child Benefit and either you or your partner had income over £60,000 (High Income Child Benefit Charge). You had capital gains above the annual exempt amount (£3,000 in 2025/26) from selling assets. You had income from a trust or settlement. You received a P800 calculation from HMRC indicating you owe tax that cannot be collected through your tax code.

What Is the Registration Deadline?

The registration deadline for the 2025/26 tax year is 5 October 2026.

Missing this deadline does not automatically trigger a penalty — HMRC typically charges penalties for late filing of the return itself (due 31 January 2027) rather than for late registration specifically. However, registering late can delay your receipt of a UTR number, which you need to file your return. Getting your UTR can take up to 10 working days, so do not leave registration until close to the filing deadline.

What You Need Before You Register

Before starting the registration, have the following ready:

Your National Insurance number. Your personal details (date of birth, address, phone number). Your business name (if you are trading under a name other than your own). The date you became self-employed or started receiving the income. Your business address (your home address is fine for most sole traders). Your business type and a brief description of what you do.

How to Register — Step by Step

Method 1: Online (fastest — recommended)

Go to: gov.uk/register-for-self-assessment

Select your reason for registering (self-employed, not self-employed but need to file, or a partner in a partnership).

If you are self-employed, you will complete form CWF1 online. This takes approximately 10 to 15 minutes.

You will be asked to create a Government Gateway account or log into an existing one. If you already have a Government Gateway account for another purpose (such as checking your tax code), use that same account.

Once submitted, HMRC processes your registration and sends your UTR number by post to your registered address. This typically takes 10 working days, though it can be longer during busy periods (October is particularly busy as it is the registration deadline).

Method 2: By phone

Call HMRC's Self Assessment helpline: 0300 200 3310 (Monday to Friday, 8am to 6pm).

Tell them you need to register for Self Assessment and the reason. They will take your details over the phone and post your UTR to your home address.

Method 3: By post

Download and complete form SA1 (for non-self-employed registration) or CWF1 (for self-employment registration) from gov.uk. Post to the address on the form. This is the slowest method and not recommended unless you have no internet access.

What Happens After You Register

HMRC sends your UTR (Unique Taxpayer Reference) number by post. This is a 10-digit number that identifies you for Self Assessment purposes. Keep it safe — you will use it every year.

HMRC sets up your Self Assessment account. You can access this through your Government Gateway account at gov.uk/personal-tax-account.

HMRC sends you a notice to file (SA316) reminding you to file your return for the relevant tax year. The filing deadline for an online return is 31 January following the end of the tax year.

For the 2025/26 tax year (6 April 2025 to 5 April 2026), the online filing deadline is 31 January 2027.

Penalties for Late Registration

While HMRC's formal penalty for failing to notify of a new source of income is based on the potential lost revenue, in practice the most common financial consequence of failing to register on time is the late filing penalty on the return itself — £100 from the day after the deadline, with additional daily and further penalties if the return remains outstanding.

If you have only recently become aware of your obligation to register, contact HMRC or an accountant immediately. Voluntary disclosure almost always results in a more favourable outcome than being identified by HMRC.

After Registration — Getting Organised for Your First Return

Once registered, set up a simple system for keeping records:

Keep all receipts related to business income and expenses. Use a separate bank account for business transactions (not legally required but strongly recommended). Note the dates and amounts of all business income received. If you use an accountant, send them your records promptly — do not wait until January.

If you are within the Making Tax Digital for Income Tax threshold (over £50,000 from self-employment or property), you also need to set up MTD-compatible software immediately and begin quarterly digital record-keeping.

A Real-Life Example

He came to us in November and we registered him for Self Assessment that day using form CWF1. His UTR arrived within 10 working days. We then prepared his 2025/26 Self Assessment return, claimed his vehicle mileage (45p per mile for the first 10,000 miles), his mobile phone business proportion, and a set of equipment he had purchased for the job.

His return was filed in May 2026 — well before the January 2027 deadline. He received a small refund because his trading allowance and expenses reduced his liability below the National Insurance threshold.

Frequently Asked Questions