Congrats!
Chances of acceptance vary. Some places have interviews for people they plan to accept just to make sure they aren't crazy. Others use the interview as part of the admissions process and cut people post-interview. Most professors plan to accept 1 student per year, rarely 2, and sometimes they choose to admit no one at all. So if you go and there are, say, 5 people for your prof, you can reasonably infer a 17% chance ceteris paribus (this is including the possibility that they accept no one and does not take into account that most professors desire to admit a student from interview) or higher (if they admit more students than they anticipate accepting their offer).
But ignore those very very specific probabilities because there are way too many variables at play here, as I hope all the disclaimers I used in the above example proved. Just do your best, do your research, and good luck! It's impossible to really say your chances, only that they are better than if you received no interview at all.