Frequently Asked Questions
Quick answers to common Self Assessment questions
When do I need to register for Self Assessment?
You need to register by 5 October after the end of the tax year in which you became self-employed. For example, if you started self-employment in 2024/25, register by 5 October 2025.
What's the deadline for filing my tax return?
For online returns, the deadline is 31 January after the end of the tax year. Paper returns are due by 31 October. For 2024/25, file online by 31 January 2026.
How much tax will I pay?
It depends on your profit. The first £12,570 is tax-free (Personal Allowance). After that: 20% basic rate up to £50,270, 40% higher rate up to £125,140, and 45% additional rate above that. Plus National Insurance.
What's the difference between income and profit?
Income (turnover) is the total money you received. Profit is income minus allowable business expenses. You pay tax on profit, not income.
What expenses can I claim?
You can claim expenses that are 'wholly and exclusively' for business: office costs, travel, equipment, software, professional fees, and more. For mixed-use items, claim the business portion.
What are Payments on Account?
Advance payments towards next year's tax bill. If your tax bill is over £1,000 (and mostly from self-employment), HMRC asks you to pay half the previous year's bill in January and half in July.
What's a UTR?
Your Unique Taxpayer Reference – a 10-digit number HMRC uses to identify you for Self Assessment. You get one when you register.
What happens if I miss the deadline?
Late filing: £100 penalty immediately, plus more if you're months late. Late payment: 5% penalty after 30 days, plus interest. File and pay as soon as possible to minimise penalties.
Do I need an accountant?
Not required, but often helpful. Many sole traders do their own returns using HMRC's online service or software. Complex situations (multiple income sources, VAT, employees) benefit from professional help.
How long should I keep records?
Keep records for at least 5 years after the 31 January deadline. HMRC can open an enquiry within this period and ask for evidence.
Have more questions? Check out our detailed guides or try the calculator to estimate your tax.
Ready to run the numbers?
Use our free tax calculator to estimate your Income Tax and National Insurance.
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