How are the MTT prize pools calculated?

I’ve been looking at the payouts of the MTTs and can’t figure how the payout is split. What calculates the number of people who receive prizes and how much each of them receives? Is it the same for every tourney or do some give more to fewer positions?

Guess it’s not that important, but I it would be nice to know what will be up for grabs if more people join after I’ve registered.