How much (%) should I charge for additional revisions?

I�m just beginning my professional journey, in a month or so done with college and all that. I decided to start off with an hourly rate and then when I get a grip of how much time/money something�s worth, I�m gonna introduce some bundles. But that�s still a bit too far into the future.

Right now I need to know how much I should charge for additional revisions. I include 3 free revisions per project that I do not charge anything for. It�s all included in my hourly rate. But I do have a client right now who wants to do revision after revision, and doesn�t even give me any good feedback and is constantly changing their mind about the end product. I would really appreciate any and all tips concerning this issue

that client sounds like cancer, id drop them tbh.. But since you give 3 revisions for free i would say like 5% of the value of the total piece per revision after that.