Let say I do some trade operations, such as buy an asset at X price and sell at X + P%.
Buy and sell have both a fees of Y.
How much percentage should I add to get X + P% compensating the fees on both operation?
Tried P+Y+Y%, but of course the trade ends with a gain < of X + P%
Percentages are not additive: for instance, if you subtract $10\%$ from a number and then add $10\%$ of the new number's value back, you end up with a number $1\%$ smaller than you started with. Instead, they are multiplicative: subtracting $10\%$ means multiplying by $0.9$, adding $10\%$ means multiplying by $1.1$, and $0.9\times 1.1=0.99$, a subtraction of $1\%$.
Using the interpretation given in the comments below, and using multipliers instead of percentages (so a $10\%$ fee is a multiplier of $0.9$ and a $10\%$ increase is a multiplier of $1.1$): I purchase a commodity with value $X$, and pay a fee of $YX$. The value of the commmodity increases by $T$ and then you pay a fee $YXT$. You want a profit of $P$ after subtracting the two fees.
In other words: $TX-YX-YXT=XP$, or $T-Y-YT=P$ (it should be intuitive that the percentage increase required is irrelevant of $X$). The two knowns are $Y,P$, so we manipulate the equation to get: $T(1-Y)=P+Y$ and $T=\frac{P+Y}{1-Y}$.
For instance, if you want a $20\%$ gain and there is a $5\%$ fee then $T=\frac{1.2+0.05}{1-0.05}=\frac{25}{19}$. Calculating concretely, if $X$ has the price $100$ then you pay $5$ for buying, and then it should increase its value to $\frac{2500}{19}$, and then you pay $\frac{125}{19}$ for selling, so your gain is $\frac{2500}{19}-100-5-\frac{125}{19}=20$.