I am not affiliated with this guy. Just find his video when browsing and notice it is very useful and clear. This guy is really doing a great Job in explaining Tax on General Investment (non ISA) with real number and work out example.
I just wonder What about the people who trade multiple times say a few thousands in a year making having gain and loss in more than 100 different stocks using the same money? I doubt anyone will be able to trace it. I also doubt any trader will ever do like what is described in the video. The amount of time that you need to spend comparing to the gain you have made does not make it worthy.
Could you not just see what you originally have in the account on the start of the tax year and see how much you gain by the end of the tax, given no money is added deduct the two and that is your gain in a particular tax year ??
Most people have their account under ISA and only use general invest for the stocks are not available under ISA account such as many chinese stocks, penny stocks, etc… So the amount of gain under invest account will be far less than £12,300 a year. Do you still need to calcaulate that when it is is very obvious your gain is much lower the the threshold ??