How to Register for Self Assessment Online (Step-by-Step)

If you had untaxed income in the 2025/26 tax year, your deadline to register for Self Assessment is 5 October 2026.

Registering is free and takes about ten minutes. What takes longer is everything that happens afterwards — HMRC processing the form, posting your UTR, setting up your sign-in. HMRC’s own guidance says it usually responds within 21 days and longer in busy periods, and late September is the busiest period there is. Leave it until then and you can find yourself with a filing deadline you cannot physically meet.

One thing has changed this year that most guides have not caught up with: new HMRC users now create a GOV.UK One Login rather than a Government Gateway ID. If you are following instructions written before February 2026, the screens will not match.

Do you actually need to register?

You must send a Self Assessment tax return if any of these applied in the tax year:

• You were self-employed as a sole trader and earned more than £1,000 — that is gross income, before expenses
• You were a partner in a business partnership
• You had Capital Gains Tax to pay
• You had to pay the High Income Child Benefit Charge and did not pay it through PAYE
• You are an off-payroll worker repaying a student or postgraduate loan

You may also need to file if you had untaxed income from property or land, tips and commission, savings interest, dividends, foreign income, or any taxable UK income while non-resident.

Two corrections worth making, because both are widely got wrong online.

The trading income threshold is still £1,000. The government announced in March 2025 that it would rise to £3,000, and Budget 2025 extended that plan to property and other income. No commencement date has been legislated — the only official timing is “within this parliament”. As at August 2026 the threshold is £1,000, and plenty of articles imply otherwise. Note also that when the change does arrive it removes the return requirement, not the tax — income between £1,000 and £3,000 will still be reportable through a simpler service.

The £100,000 and £150,000 income triggers are gone. Up to 2022/23, PAYE-only taxpayers had to file if income exceeded £100,000. For 2023/24 it was £150,000. From 2024/25 the criterion was removed entirely. There is now no income-level trigger for PAYE-only employees — you could earn £300,000 through PAYE and not need to file, unless something else on the list applies.

High Income Child Benefit Charge has also changed. Since summer 2025 you can pay it through your PAYE tax code instead of filing a return. HICBC now only forces you into Self Assessment if you have not chosen the PAYE route.

If you are unsure, HMRC’s checker at gov.uk/check-if-you-need-tax-return settles it in under two minutes.

The 5 October deadline

Register by 5 October following the end of the tax year in which the income arose.

If you register late, HMRC issues a letter or email giving you a different filing deadline — three months from the date on that correspondence. But the payment deadline does not move. Tax is still due by 31 January.

You may also face a “failure to notify” penalty, which is tax-geared: calculated on the amount still unpaid at 31 January. Register late and pay on time and it can come to nothing. Register late and pay late and it compounds.

Which route applies to you

GOV.UK now routes everyone through a triage tool — “Check how to register for Self Assessment” — which picks the right form from your circumstances. Behind it sit five forms.

The key difference: CWF1 registers you for Self Assessment and Class 2 National Insurance together. SA1 registers you for Self Assessment only. If you are trading, use CWF1 — otherwise your NI record has a gap, and that affects your state pension entitlement.

A trap worth knowing. If you already registered for Self Assessment for some other reason — say rental income — and then start trading as a sole trader, you must register again using CWF1. The system does not enrol you for Class 2 NIC automatically.

Registering step by step

If you’re self-employed (CWF1)

Step 1 — Go to gov.uk/become-sole-trader/register-sole-trader. This is the sole trader entry point.

Step 2 — Sign in or create sign-in details. You will be offered Government Gateway, GOV.UK One Login, or creating new sign-in details. If you have an existing Government Gateway account, use it. If not, you will create a GOV.UK One Login — email address and password, with identity verification using a passport or driving licence.

Step 3 — Have these ready: National Insurance number, date of birth, home address, contact details, the date you started trading, what your business does, and your business address if different from home.

Step 4 — Complete and submit the CWF1. Ten minutes at most.

Step 5 — Wait for your UTR. HMRC usually contacts you within 21 days, and longer during busy periods. Longer again if you live overseas.

Step 6 — Check the HMRC app or your personal tax account. If you registered online, your UTR often appears here before the letter arrives. This is the fastest route and most guides do not mention it.

If you’re not self-employed (SA1)

Step 1 — Go to gov.uk/register-for-self-assessment and work through the triage tool.

Step 2 — Choose how to sign in. SA1 has a useful option the other forms lack: you can either sign in with an account, or just use an email address and receive a confirmation code. No account needed.

Step 3 — Have ready: National Insurance number, date of birth, address, contact details, and the reason you need to file — property income, dividends, capital gains, foreign income, or similar.

Step 4 — Submit. HMRC usually responds within 21 days.

Step 5 — Your UTR arrives, usually within 21 days, and you can then set up your online account to file.

If you’ve registered before

If you previously filed but did not file a return last year, your Self Assessment account may need reactivating. HMRC’s own warning is blunt: your tax return may be delayed if you file it without reactivating an existing account.

You do not get a new UTR. You keep the one you already have — check old HMRC correspondence, your personal tax account or the HMRC app.

The sign-in change nobody told you about

This is the biggest practical change to registration in years.

From 9 February 2026, individual customers without an existing Government Gateway account create a GOV.UK One Login instead. That means most new Self Assessment registrants.

One Login uses an email address and password rather than a twelve-digit Government Gateway user ID, and typically requires identity verification with a passport or driving licence. HMRC has said it will eventually replace all other sign-in routes.

If you already have a Government Gateway account, do nothing. You keep using it and HMRC will contact you when it is your turn to move. Existing individual customers migrate from 2027; agents and organisations by 2030.

Ignore any guide that talks about waiting ten working days for an activation code in the post. That was a Government Gateway step and it is being superseded for new individual users. A lot of otherwise reliable guidance still includes it.

What happens after you register

Your UTR arrives — ten digits, by post, usually within about 21 days. You need it to file.

Set up your online account if you have not already, using One Login or Government Gateway.

Start keeping records. For sole traders this matters more than it used to, because of Making Tax Digital.

Note your deadlines. For the 2025/26 tax year: paper return by 31 October 2026, online return by 31 January 2027, and payment by 31 January 2027. If you want tax under £3,000 collected through your PAYE code instead, file online by 30 December 2026.

Check whether payments on account apply. If your tax bill exceeds £1,000 and less than 80% was collected at source, HMRC asks for two advance payments toward next year’s bill — 31 January and 31 July, each half of the previous year’s liability. First-timers are often blindsided by this: your first 31 January bill can be 150% of the tax you expected.

Does MTD for Income Tax apply to you?

Making Tax Digital for Income Tax went live on 6 April 2026. This is not upcoming — it is in force now.

If you are a sole trader or landlord with qualifying income over £50,000, you should already be using MTD — keeping digital records and submitting quarterly updates on 7 August, 7 November, 7 February and 7 May, alongside a year-end return.

HMRC identifies you, not the other way round. They review your Self Assessment return each year and write to confirm when you must start.

Partnerships are not yet in scope. HMRC has not published a timeline.

A concession for the first year: no penalty points for late quarterly updates during 2026/27. Digital records and quarterly updates are still required, and late return and payment penalties still apply — just not points for late quarterly updates.

Note that MTD-mandated taxpayers are now on a points-based penalty system rather than the standard £100 late filing penalty. It extends to everyone filing a personal Self Assessment return from April 2027.

Frequently asked questions

How long does it take to get a UTR?
HMRC’s guidance says it will usually contact you within 21 days of receiving your form, and may take longer during busy periods — which includes the run-up to 5 October and January. Longer again if you live overseas. Check the HMRC app or your personal tax account first, where it often appears sooner.

Can I register after 5 October?
Yes, and you should if you have missed it. HMRC will give you a filing deadline three months from their letter. The payment deadline stays at 31 January, and a failure to notify penalty may apply based on tax unpaid at that date.

Do I need to register if I earned under £1,000 self-employed?
No. The £1,000 trading allowance covers you and you do not need to tell HMRC. Note this is gross income before expenses. The announced increase to £3,000 has no start date and is not yet in force.

I’m a company director — do I need to file?
Not automatically. Being a director is not itself a filing trigger. You file if you have untaxed income such as dividends above your allowance, or if another criterion applies.

Can I register by phone or post?
Paper versions of CWF1, SA400, SA401 and SA402 exist, but online is faster and gives you a submission confirmation. Paper adds weeks.

What if I no longer need to file?
Tell HMRC. If you stop trading or your circumstances change, you must notify them — otherwise notices to file keep coming, and a £100 penalty applies for each one you ignore, even with no tax to pay.

Getting it right first time

Registration itself is not hard. What creates problems is the timing — leaving it close to 5 October, waiting on a UTR that has not arrived, and discovering in January that payments on account have made your first bill half again as large as you budgeted for.

SmartFiling handles Self Assessment and MTD for Income Tax on a fixed fee, covering registration, quarterly updates where MTD applies, and the year-end return. Every submission is reviewed by an ICAEW Chartered Accountant, and turnaround is three weeks from receiving your records.