Do you need to register?
You register if you must complete a return for the tax year and either have never filed one, or did not need to file last year. If you previously registered but skipped a year, GOV.UK says you may need to reactivate your account, which the online service walks you through.
Check first whether you need to send a return at all. Registering when you do not need to only creates paperwork.
The deadline
You must tell HMRC by 5 October following the end of the tax year. For the year ended 5 April 2026 that is 5 October 2026. Missing it can lead to penalties, so register as soon as you know you need to. Self-employed people should register as soon as they start trading rather than waiting for the deadline.
What happens after you register
HMRC sends you a UTR, a 10-digit number that identifies you for Self Assessment. Once you have registered you also receive an activation code by post, which you need to enter to access your online account and file. This can take time, especially if you register close to the deadline, so do not leave it to the last minute.
Keep your UTR safe. You will need it for your return, to make payments and to deal with HMRC about your tax.
If you registered late
If you register after 5 October 2026, HMRC sets a different filing deadline, three months from the date on its letter or email. The tax you owe is still due by 31 January 2027.
Registering as a company director
Directors who need to file a personal return register in the same way. Because your salary and dividends come from the company's figures, it usually makes sense to have the company accounts and personal return prepared together.
Need a hand with your return?
We prepare and file Self Assessment returns for directors, sole traders and landlords, and tell you exactly what is due and when before anything is submitted. Call 0114 327 1480.