A question about taker/maker fees

Hello I got a question that popped into my mind all of a sudden after 1 year almost full day trading...The 0.1 average taker and maker fee is a fee subtracted by the amount of gain you're earning after having openened a position, or is it subtracted in advance just because you opened a position same as it happens in forex trading and you have to recover that 0.1% before being in profit?(This can be in spot or margin, sice I know that futures are higher spreads).

Let me do an example: you invest 100.Do you pay the 0.1% fee of 100 of the capital earned? For example, 100+20% gain = 120, then you have subtracted the 0.1% = 119.88 net profit.Or have you subctracted the 0.1% as soon you open a position? For example you invest 100, - 0.1% = 99.9 the real amount you're investing, that you have to recover. So, +20% gain = 119.88Same when you loss.This indeed affects the strategy. In case I try to invest 100 and earn 3 (+3% gain) should I count 3 earned - 0.1% or should I count 100 - 0.1% + 3% ? To understand better, assuming that I buy and sell at the same price, have I lost 0.1% + 0.1% in advance or have I lost nothing since I haven't generated neither profits nor losses.

Hope to have been clear... Thank you