How to calculate total proceeds - day trading in shares

I have done some day trading in stocks and shares, and I am confused as to how to calculate the total proceeds that are asked for in the self assessment form. It asks whether I disposed more than £49,200 in the form. Later in the form it also asks about total 'proceeds'... If I have used a £20k investment to buy and sell loads of different types of shares over a few months, making profit/losses varying around £100-£500 from the £20k principle, how do I calculate the total that I have disposed of? I am assuming it isn't £20k for every time I sell the shares, otherwise I would have disposed of over £1 million, as I have done LOTS of transactions. Can you help explain how this is calculated? Thanks

Hi,
Please refer to guidance at:
Shares and Capital Gains Tax (Self Assessment helpsheet HS284
​​​​​​​Thank you.