It depends on:
1.) How much you keep down when you're not purging
2.) The methods you use to purge
3.) How efficient you are at purging
For instance. When I'm keeping down only 500 calories and binging/purging, I'm losing weight. Not so much if I'm eating at maintenance and binging/purging on top of that.
The only way to make sure for certain that you're getting rid of all the calories is through exercise or prolonged restriction/fasting to compensate. Purging by vomiting works, but is unreliable if you have a weak gag reflex. Laxatives don't do anything for calories; they only get rid of water weight in the short-term.