How much does being on the Stanford waitlist actually improve your chances of admission?

Being on the Stanford waitlist means you are still admissible, but in practical terms the odds are usually quite low. Stanford, like most highly selective schools, uses the waitlist to manage class size, and how many students they admit from it changes a lot from year to year.

In some years Stanford has taken very few or even no students from the waitlist, while in other years they have admitted a modest number. That means the waitlist is real, but it is not something you should count on. It is better to think of it as a small remaining possibility rather than a likely outcome.

What the status means is basically this: your application was strong enough to stay under consideration, but Stanford did not have room to offer you a spot in the first round. It does not mean you are close in a ranked line, because Stanford does not simply go down a fixed list. They usually revisit the waitlist based on what kinds of students they still need in the class.

So yes, it improves your chances compared with being rejected, since you still have a path to admission. But it does not improve them enough to make Stanford a realistic plan. You should move forward as if you will attend another school, submit your enrollment deposit elsewhere by the deadline, and only treat Stanford as a bonus possibility.