Self-assessment tax software company, GoSimpleTax, has launched a free online calculator to help the UK’s growing side-hustle workforce check whether they owe tax, following a renewed HMRC push for people to review their obligations ahead of the Self-Assessment registration deadline.

With two in five Brits (39%) currently engaged in at least one side hustle and an average income of almost £11,000, hundreds of thousands risk penalties if they fail to check whether they need to file a tax return for the 2024 to 2025 tax year.

Under current rules, anyone earning more than £1,000 from self-employed work, freelance projects, or side hustles must register with HMRC and submit a Self-Assessment tax return. Even those earning less are strongly advised to keep records of all income and expenses.

The recommended deadline to register for self assessment for the tax year 2024-25 is 5 October and the deadline to file online and pay any tax owed for the year is 31 January 2026.

GoSimpleTax’s calculator estimates take-home pay by deducting Income Tax and National Insurance from a user’s total side-hustle income. Users can also factor in business expenses before seeing their estimated tax bill. This gives side hustlers a clear, instant picture of what they might owe, and time to plan ahead.

Mike Parkes, Technical Director at GoSimpleTax, said: “Side hustles are booming, but many people are unaware of their tax responsibilities. If you earn more than £1,000 a year from activities such as selling on Vinted or Etsy, delivering via Uber Eats or Deliveroo, creating content on TikTok, or freelancing on platforms like Upwork, you may need to register with HMRC and file a tax return. That £1,000 threshold sounds high, but it’s just £84 a month – easy to exceed without realising. Our free calculator helps people check what they owe quickly, plan ahead, and avoid unexpected tax bills or penalties.”