Waitlist chances are usually impossible to determine because they typically depend on individual decisions that are impossible to predict.
Like, the chain has to start with too many admits not enrolling such that the college has to go to the waitlist to fill out their target class size. How many slots that will create is highly variable, and sometimes it is none at all (in which case the college might be overenrolled, which happens sometimes).
Then the question is WHO didn’t enroll? Most colleges reserve the right to pick anyone they want off the waitlist, so they can meet various goals for their enrolled class. One of those goals can be budgetary, and in fact there is a so-far-successful lawsuit alleging a lot of supposedly need blind colleges actually were need aware when it came to their waitlist decisions. But they could also be looking for certain academic interests, certain activity interests, various demographics (to the extent allowed by law), and so on.
OK, so not only do you need too many admits to turn down the college’s offer, you need them to be the right sorts of admits such that offering you in particular a spot, as opposed to someone else on the waitlist who is different from you, would help that college hit its targets for the class.
Which might happen. But probably will not. But it might. But there is no real way to put a number on that probability, otherwise than to note usually for the types of colleges you are looking at, it doesn’t happen for many.