You need to register for Self Assessment if you have to send a tax return and didn’t send one last year.
How you do this depends on whether:
You register online even if you want to send a paper return.
When to register
Register by 5 October following the end of the tax year you need to send a tax return for. The tax year is from 6 April to 5 April the following year.
If you register late, you won’t get a penalty as long as you pay your Self Assessment bill in full by the deadline.
It can take 20 working days (this is usually 4 weeks) to complete the registration process. Allow time so you can send your tax return by the deadline. This is 31 January, or 31 October (3 months earlier) for paper returns.
Your Unique Taxpayer Reference (UTR)
You’ll get a Unique Taxpayer Reference (UTR) automatically when you register. Find out what to do if you can’t find your UTR.