Register for Self Assessment by 5 October: Who Must, How, and What Happens If You Miss It
Started self-employment, earned untaxed income or received dividends? You must tell HMRC by 5 October. Here is who needs to register, how to do it and how to avoid penalties.
If you started trading as a sole trader, became a partner, or received income that was not taxed at source in the last tax year, HMRC expects you to register for Self Assessment by 5 October following the end of that tax year. For income in the 2025/26 tax year, the deadline is 5 October 2026.
Who needs to register?
You usually need to register if, in the tax year, you:
- Earned more than £1,000 from self-employment (above the trading allowance)
- Became a partner in a business partnership
- Received untaxed income such as rental profits, foreign income or significant savings interest
- Received dividends above the dividend allowance that are not covered by other reporting
- Need to pay the High Income Child Benefit Charge (unless paid through PAYE)
- Made capital gains that need reporting
Company directors are not automatically required to file, but many do because of dividend income.
How to register
- Sole traders register for Self Assessment and Class 2/4 National Insurance in one step via the HMRC online service.
- Non-self-employed individuals (e.g. landlords) use the separate SA1 route.
- Partners register individually, and the partnership registers too.
HMRC then posts your Unique Taxpayer Reference (UTR). Allow up to 15 working days, longer if you live abroad.
What if you miss 5 October?
Missing the registration deadline is a "failure to notify". If you still file and pay by 31 January, there is usually no penalty. If tax is paid late because you did not notify, HMRC can charge a penalty based on a percentage of the unpaid tax, depending on whether the failure was careless or deliberate.
Plan the first bill
Your first Self Assessment bill can be a shock: the balancing payment for year one plus the first payment on account for year two, both due on 31 January. Read our guide to payments on account to plan cash flow.
Get it done for you
Not sure whether you need to register? Talk to our qualified, HMRC-registered accountants — we handle registration, bookkeeping and returns for sole traders and contractors.