So to confirm these calculators assume you are running in a pool? But in this case the calculators must assume that the pool will win a certain percentage of the block rewards right? How would they even begin to guess what that percentage would be?
This is how I understand it: Imagine that there are only two mining pools, and each of them holds exactly half of the total hash power of the Bitcoin network. Logically, this means that each of them will mine an equal percentage of blocks in the long run.
So, in this context, the calculators don't need to know the winning percentage; they only need to determine the percentage of your hash power in relation the network's total power. Of course, it can happen that some pool is extremely unlucky for a while, but it all tend to balance out over time.