So to confirm these calculators assume you are running in a pool?
Your profit is estimated to be (Your hash rate / total hash rate) * reward amount
If you join a mining pool, the equation should give you a good estimation of your profit.
If you are a solo miner, it's more like that you are gambling.
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?
Regardless of what percentage of blocks are mined by the mining pool, your profit is estimated using the above equation.
The bigger the hash rate of the pool, the more accurate the equation can be.