Close to nada for 99.99% of the acting world. Less than nada if you include the cost of pictures and shmoozy lunches and generally "marketing yourself"—i.e. gas and parking for auditions and industry mixers.
As we all know, those Hollywood mega-stars make extremely good money (not nearly as much as you read in the press, though), but that almost certainly won't be you, no matter how talented you are. And how great are most of their lives anyway? Multiple divorces, constantly being harangued by the paparazzi, no privacy, etc. You have to think about the kind of personality that would be willing to sacrifice almost everything to be…famous. Lots and lots and lots of people think that being famous is not a good thing and are personally secure enough so that having a spouse and kids who love them, a stable life/job/jump shot…defines a successful life. Having strangers ogle one’' life was something "losers" aspired to have…. If you are set on getting into this business, be prepared to struggle for every dime, and to make most of your moolah doing a secondary job, most likely in some sort of food and beverage establishment. Get used to the words "Order up!"—and then having to kiss the butts of your classmates from school who went on to get law, accounting, medical, and other degrees—and who now make you wait on them.
Keep in mind, that even if you are able to book some work, there are expenses you may not realize. $500 for headshots every couple years (or every time your look changes significantly), hundreds of dollars for postage and envelopes, for registering on casting websites, for hiring a web designer for your personal website, and so on. You’'e an actor, but you’re also a businessman, so you've got a lot of business expenses. And then there’s SAG (Screen Actor's Guild)—the union you want to get into if you want to be taken as seriously as De Niro, and at the same time make some serious dinero. Once you become SAG-eligible (usually by getting vouchers working as an extra or by getting a speaking role in a union project, otherwise known as being "Taft-Hartley'ed"), you have to pay dues. That's more than a couple grand up front, plus another $100+ a year. And if you're only working 15-20 days a year making a few hundred bucks a day…well, we'll let you do the math. After all, unless you're Brad, you're going to have plenty of time on your hands.