Add up all self-employed income received in the tax year
Subtract allowable business expenses
Subtract capital allowances if applicable
Work out your net self-employed profit
Add any other taxable income you have
Deduct personal allowances and any reliefs you qualify for
Apply the relevant income tax rates to the taxable income
Calculate Class 2 National Insurance if applicable
Calculate Class 4 National Insurance if applicable
Add any student loan repayments if applicable
Add any payments on account if required
Subtract any tax already paid through PAYE or other sources
The result is the tax still owed or the refund due