Maybe just UK specific, but do you use Emma to track where you are with your PSA and your ISA limits? If so, how do you have it set up? I find the exclusion of transfers makes it messier to get a total on these.
I don’t know how to deal with what you’re talking about, but I can say that in order to track future tax expenses that I need to pay later in the year, I mark them as a custom ‘Loan’.
So, for example, if I know that in January I will need to pay £10k for my Self Assessment Tax, I create a loan in order that I can recognise the ‘negative balance’ within the app.
Obviously it’s not a loan, but this is the best I can do. And it’s not completely wrong, because it is a future ‘cost’ I’m planning to incur.
(I guess you could do something similar, and use a custom loan which you slowly decrease as you pay money into your ISA. The loan sort of simulating that this is something that you’re actively paying through out the year.)