Leaving PAYE and Continuing Self Employment

I have been PAYE and self employed for a few years. I do annual self assessment. I've decided to leave PAYE end of August 2024 and concentrate on my self employed journalism from Septeber 2024. How do I calculate my Personal Tax Allowance for the remainder of this tax year 2024/25 and will I need to pay NICs - I reckon I could earn around £20,000 in a full year. Anyone for guidance on this please

Hi,
You would need to see how much you have earned PAYE and self-employed from 6 April 2024 up until you left PAYE to see how much income you had earned.
The personal allowance for 2024/25 is £12,570. When you complete your tax return for the 2024/25 tax year, you would complete the employment income pages (ensuring to include your leaving date where applicable) and also your self-employment income and this will be calculated automatically. 
Thank you.