If you have recently started a business in Sussex — or have been earning income not declared to HMRC — you will need to register for self-assessment. It is a straightforward process, but the deadlines matter. Miss them and you face automatic penalties.
When do you need to register?
The registration deadline is 5 October following the end of the tax year in which you started earning the income. So if you started a business in 2025/26 (ending 5 April 2026), the deadline is 5 October 2026. Missing this deadline can trigger a penalty even if no tax is ultimately owed.
What you will need before you start
- Your National Insurance number
- Your personal details (name, address, date of birth)
- The date you started your business or began earning the income
- Your business name and description of what you do
- A Government Gateway user ID (you can create one during the process)
How to register: step by step
Go to the HMRC website and navigate to the self-assessment registration section. Sign in to your Government Gateway account. Complete the online registration form — for sole traders, this is form CWF1. For landlords with no self-employment income, use form SA1.
HMRC will send your UTR (Unique Taxpayer Reference) by post within 10 working days. Keep this safe — you will need it for all future HMRC correspondence. Once you have your UTR, activate your online self-assessment account to file returns.
What happens after you register?
HMRC will expect you to file a return each year until you formally notify them to stop. If you stop being self-employed or no longer need to file, you must deregister — otherwise HMRC will continue to expect returns and issue penalties for non-filing.
Common mistakes to avoid
- Leaving registration too late — postal delays do happen
- Registering under the wrong category
- Not keeping your UTR safe and accessible
Talk to us about your situation
Our chartered accountants work with small businesses, landlords and contractors across Surrey, Kent and Sussex. Get in touch for a free initial consultation.
