If you started working for yourself between 6 April 2025 and 5 April 2026, HMRC needs to hear from you by Monday 5 October. If that’s you, do it this weekend. It’s a quick online job today and an awkward one in January.
This catches new sole traders, new business partners, and anyone with side-hustle income above the £1,000 trading allowance. If you trade through a limited company, this isn’t the company’s deadline, since it registers for Corporation Tax separately. You may still need a personal return yourself, for example because of dividends, so check.
The penalty for missing Monday is based on tax that ends up paid late. Register late but still file and pay everything by 31 January, and in most cases it comes to little or nothing. That isn’t a reason to leave it. Your Unique Taxpayer Reference arrives by post and can take a week or more. Leave registration until December and you could be filing your first return against the clock, with a bill you haven’t budgeted for.
Ten minutes now buys you four calm months to get your first return right. Who do you know who started something on the side last year and hasn’t told HMRC yet?