The answer is quite straightforward.

Say you buy a stock at 10$ per share at time t, and you sell at 11$ 10 days later. Of course your return is 10% or 1$

Since it is a risky return, so you can not discount it with a riskfree rate. Nobody knows what discount factor should we use.

Just use the most simple way to calculate the return, just as your parents calculate the investment return on stocks (if they trade stocks :-) ).