If you are self-employed for any period during a tax year then you will need to complete a self-assessment tax return this includes;

A full tax year self employed

Part tax year as PAYE* and part self employed

Not working and then going self employed

*PAYE is the tax you pay under The Pay as You Earn (PAYE) system. This is how you pay both your income tax and national insurance (NI). Every time you’re paid, your company takes your tax and NI from your wages and sends it on to HMRC.