How to register for Self Assessment
Tell HMRC you need to send a tax return, pick the right registration form, and get your UTR before the 5 October deadline.
Last checked 12 August 2026
Before you start
The registration form asks for all of these, so have them to hand.
Your National Insurance number.
The date your self-employment or untaxed income started.
What your business does, and the name you trade under if it isn't your own.
Your home address and contact details.
A Government Gateway user ID — you can create one while you register.
Check whether you need to send a tax return
You need to register if you were self-employed and turned over more than
£1,000 before expenses, took more than £1,000 in rent before expenses, or
had income HMRC doesn't already tax at source — dividends, savings
interest, or foreign income above the allowances. HMRC's checker also
covers the less obvious cases, like the High Income Child Benefit Charge
or selling an asset at a gain.
Check on GOV.UK →Register by 5 October after the tax year ends
The deadline is 5 October following the end of the first tax year you
need to report. Don't leave it to the deadline week: everything else
hangs off the reference HMRC sends back, and it comes by post.
Deadline
5 October 2026, for the tax year that ended on 5 April 2026.
Pick the form that matches how you earn
Self-employed sole traders register for Self Assessment and Class 2
National Insurance together on form CWF1. If you're registering for
another reason — rental income, dividends, other untaxed income — use
form SA1 instead. Partners register themselves on SA401, and the
partnership itself is registered separately on SA400.
Register on GOV.UK →Sign in with your Government Gateway details
You complete the form inside your HMRC online account, so you need a
Government Gateway user ID and password. You can create one as part of
registering if you don't have one — use the same sign-in every year
rather than ending up with two accounts.
Sign in to HMRC online services →Wait for your UTR to arrive
Once you're registered, HMRC posts your 10-digit Unique Taxpayer
Reference, then sends an activation code for the online service
separately. Both arrive by post, so allow a couple of weeks before you
can file anything.
Good to know
Registering isn't the same as filing. Your first return has its own
deadline, months later.
Keep records from day one, then file
From the date you registered, HMRC expects a record of everything you
earn and everything you claim. The return itself is due by 31 January
after the tax year ends if you file online, or 31 October if you file on
paper.
Deadline
31 January 2027, for the tax year that ended on 5 April 2026.
Common questions
Registering, in practice
I earned less than £1,000 — do I still need to register?
No. The trading allowance covers up to £1,000 of self-employed income
before expenses, and you don't have to tell HMRC about it. You can still
register voluntarily if you want to claim a loss or pay voluntary Class 2
National Insurance towards your State Pension.
I've been registered before. Do I register again?
Yes, but you keep your original UTR. Re-register on form CWF1 and quote
the reference you already have rather than applying for a new one.
What happens if I miss 5 October?
Register as soon as you realise. HMRC works out a failure-to-notify
penalty from the tax you owe, so registering late but still paying in
full by the payment deadline usually leaves nothing to pay.
Does this sign me up for Making Tax Digital?
No — they're separate. Making Tax Digital for Income Tax has its own
sign-up and its own start date, which depends on your income. HMRC's
guidance tells you whether it applies to you yet.
Next steps
What most people need straight after registering.
Registered? Now keep the records HMRC expects.
Bookfolio keeps your self-employment and rental records digital from day one, works out what you owe as the year goes on, and files your MTD for Income Tax quarterly updates straight to HMRC. You review every figure before anything is sent.