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Self-Assessment Tax Calculator 2025/26

Free Self-Assessment tax calculator for sole traders and the self-employed. Includes Income Tax and Class 4 NI for 2025/26.

Estimated tax bill£6,482Income Tax + Class 4 NI · profit £37,500
  • Self-employed profit£37,500.00
  • Income Tax£4,986.00
  • Class 4 National Insurance£1,495.80
  • Total Self-Assessment liability£6,481.80

Class 2 NI is voluntary for most self-employed people from 2024/25 onwards. This calculator assumes you've taken your full annual exempt amounts and that you're not Scottish (Scottish bands available in the Income Tax calculator).
How this is calculated

The maths, in plain English.

Self-Assessment for sole traders covers two main charges:

  • Income Tax — calculated on your profit (turnover minus allowable expenses) plus any other taxable income, using the same bands as employees
  • Class 4 National Insurance — 6% on profits between £12,570 and £50,270, then 2% above (2025/26 rates)

Pension contributions you make personally reduce taxable income at the basic rate automatically (relief at source) and you can claim higher/additional rate relief through the return.

Your tax bill also depends on payments on account, prior year reliefs, and other factors. This calculator is a guide — for an accurate position we recommend a proper review.

Common questions

4 questions we get asked.

If yours is not here, ring us. We answer in four rings on weekdays and write back the same day on emails.

01 When is my Self-Assessment tax due?
Your Self-Assessment tax bill for 2025/26 is due by 31 January 2027 (along with the first payment on account for 2026/27). The second payment on account is due 31 July 2027. The 2024/25 bill is due 31 January 2026 — we file early so you have months to plan, not days.
02 What about Class 2 NI?
Class 2 NI is no longer mandatory for most self-employed people from 6 April 2024. You can still pay voluntarily to keep up your state pension entitlement. We don't include Class 2 in this calculator since it's optional.
03 What expenses can I deduct from profit?
Anything 'wholly and exclusively' for business: tools, professional fees, business travel, a portion of home office costs, accountant fees, training, subscriptions. Calculate your profit (turnover − expenses) and enter that here.
04 Should I worry about payments on account?
If your Self-Assessment liability is over £1,000 and less than 80% is collected through PAYE, HMRC asks for two equal payments on account — basically half your bill in advance for the next year. We'll check whether you can reduce these (or skip them) based on your forecast.
One call. Twenty minutes.

Want a real human to walk you through this?

Free, no obligation, no email wall. Bring your last tax return, or do not.

Call 07809 590922 Or book online