How to Register for Self Assessment: A Step-by-Step Guide for New Self-Employed People

Starting out as self-employed in the UK comes with a long to-do list. Near the top of it — often not discovered until alarmingly close to a deadline — is registering for Self Assessment. This guide walks through exactly who needs to register, when, how, and what to expect once you've done it.

Who must register for Self Assessment?

You must register for Self Assessment if any of the following apply for a tax year (6 April to 5 April):

• You were self-employed as a sole trader and your gross trading income was more than £1,000
• You were a partner in a business partnership
• You were a company director (there are limited exceptions if you have no income to declare)
• Your total income was more than £100,000 from any source
• You had untaxed income of more than £2,500 — this includes rental income if not covered by the property allowance, investment income, or income from abroad
• You received income from savings or investments and you owe tax that hasn't been collected through PAYE
• You received Child Benefit payments and your income exceeded £60,000 (the High Income Child Benefit charge threshold)
• You received foreign income that is taxable in the UK
• You need to claim certain reliefs or allowances that can only be claimed through a tax return — for example, higher-rate pension relief, some Gift Aid claims, or losses to carry forward

If none of these apply, you probably don't need to file a Self Assessment return. But if you received a notice from HMRC to file a return, you must do so — even if you think you don't owe any tax.

When is the registration deadline?

The deadline to register for Self Assessment is 5 October following the end of the tax year in which you first needed to register.

Example: You started freelancing in June 2026 (the 2026/27 tax year, which runs from 6 April 2026 to 5 April 2027). Your gross income from freelancing exceeds £1,000 during that year. Your registration deadline is 5 October 2027.

Miss this deadline and HMRC can charge a late registration penalty, though in practice penalties for modest lateness when no tax was unpaid tend to be minimal. The principle is clear: register on time, even if you think your tax bill might be small.

If you've been self-employed for a while and realise you should have registered but haven't — don't wait to come forward. HMRC has a disclosure facility, and voluntarily correcting your position generally results in lower penalties than being discovered.

How to register: the step-by-step process

Step 1: Get a Government Gateway account

Everything with HMRC is now done online through the Government Gateway. If you don't already have an account, go to HMRC's website and create one — you'll need a UK mobile number and some form of ID verification (passport, driving licence, or a knowledge-based check using your credit file).

If you've previously dealt with HMRC for any reason — PAYE tax returns, VAT registration, Child Benefit — you may already have a Government Gateway user ID. If you've forgotten it, there's a recovery process via the sign-in page.

Step 2: Register as self-employed for Self Assessment

Once logged in, navigate to the "Self Assessment" section. If you've never had a Self Assessment record, you'll need to "Add a tax" or "Register for Self Assessment" — the wording changes occasionally as HMRC updates the portal.

You'll be asked for:

• Your National Insurance number
• Basic personal details (address, date of birth)
• The date your self-employment started
• The nature of your business (a broad category is sufficient)
• Whether you have any other income sources

HMRC will then set you up with a Self Assessment record and issue you a Unique Taxpayer Reference (UTR).

Step 3: Receive your UTR

Your UTR is a 10-digit number that identifies your Self Assessment record. HMRC posts the UTR to your address on record. This is not instant — it typically takes 10 working days, though it can take longer during busy periods.

Important: if you need to set up an online account to file a return, you need your UTR before you can do this. So don't leave registration until the last possible moment — if you register in late January expecting to file immediately, you may find you're waiting for a letter.

Your UTR never changes. Once you have one, it stays with you for life, even if you stop being self-employed and later become self-employed again.

Step 4: Activate your HMRC online account for Self Assessment

Once you have your UTR and you're ready to file, you'll need to activate the Self Assessment element of your Government Gateway account. HMRC will send an activation code by post (again — not instant), which you enter into the portal.

This activation step catches many people out, particularly first-timers who assume they can register and file in one continuous session. Allow at least 2–3 weeks from initial registration to being able to file online.

What happens after you register?

You'll be sent a notice to file

Once registered, HMRC will typically send you a notice to file a tax return each year. Technically, the obligation to file exists regardless of whether you receive the notice — but the notice confirms HMRC knows you're in the system.

You'll need to file by the deadlines

Online returns: 31 January following the end of the tax year. For 2026/27 (which ends 5 April 2027), the online filing deadline is 31 January 2028.

Paper returns: 31 October following the end of the tax year. The paper deadline is 3 months earlier because HMRC needs time to process paper submissions.

The filing deadline and the payment deadline are both 31 January — so you file and pay on the same day (or before it).

You'll need to pay your tax bill

Payment is due by 31 January — same day as the online filing deadline. This covers your balancing payment (the final amount owed for the year after any payments on account).

If your qualifying tax bill (income tax plus Class 4 NI) exceeds £1,000, HMRC will also require payments on account toward next year's bill:

• First payment on account: due 31 January (alongside the balancing payment)
• Second payment on account: due 31 July

The payment-on-account system catches many first-year sole traders off guard because the first January combines three amounts: the current-year balance, the first payment on account for next year, and (if you owe it) any student loan or other amounts. Planning for this from your first year of self-employment prevents a nasty surprise.

Use the Payment on Account Calculator to see what your January and July payments will be once you know your current-year tax liability.

Common mistakes when registering

Registering too late: The registration deadline is 5 October following the relevant tax year. Many people only discover they needed to register when they're preparing their accounts — often months after the deadline. Penalties for late registration are generally modest when no tax was unpaid, but it's worth getting right.

Confusing UTR with NINO: Your Unique Taxpayer Reference (10 digits) is different from your National Insurance number (letters and numbers). You'll use both. Your UTR is your Self Assessment identifier; your NI number identifies you for tax and benefits across all systems.

Waiting for HMRC's invitation: HMRC doesn't necessarily send you a registration prompt when you become self-employed. The obligation to register is yours — proactively — not something HMRC chases you about initially.

Not registering because you're under the trading allowance: If your gross self-employment income is under £1,000, you don't need to register. But "gross income" is total receipts before expenses — not profit. If your turnover is under £1,000 but your profit after expenses is much less, the allowance still applies to the gross figure.

Assuming employed PAYE means no Self Assessment: If you also have employment income through PAYE, you may still need to file Self Assessment — for example, if your employment income exceeds £100,000, or if you have self-employment income on top. The two systems can run in parallel.

After you register: keeping records

From the moment you start trading, you should be keeping records. HMRC requires records for five years after the 31 January filing deadline (so effectively about six years from the end of the relevant tax year).

Records to keep:

• All business income: invoices, receipts, bank statements showing payments received
• All business expenses: invoices, receipts, mileage logs, home office calculations
• Bank statements: ideally from a dedicated business bank account (not legally required, but strongly recommended for clarity)
• PAYE documents if you are also employed: P60, P11D, any redundancy paperwork

Digital records are fine. Cloud accounting software, a structured spreadsheet, or even photographed receipts stored in a folder are all acceptable. The test is whether you can reconstruct your business income and expenses from your records.

Starting with good record-keeping habits makes filing your return straightforward. Trying to reconstruct a year's business activity in January from a pile of receipts and bank statements is the experience most people have once and then fix.