Sole trader tax isn't a separate system — it's the same income tax bands as employment, plus Class 4 National Insurance on your profit. This estimates both from your yearly profit figure.
Your inputs
Annual sole trader profit£45,000
Turnover minus allowable business expenses — the figure that goes on your Self Assessment.
Personal allowance (0%)£12,570
Income tax owed£6,486
Class 4 National Insurance£1,946
Estimated tax + NI owed
£8,432
Take-home ≈ £36,568
Effective rate
18.7%
Set aside monthly
£703
This covers income tax and Class 4 NIC only — it doesn't account for the trading allowance, Class 2 NIC, student loan repayments, or pension contributions. Bands shown are approximate; confirm current thresholds on gov.uk before filing.