The jOBS actor took advantage of his "dumb actor" persona to win huge sums of money betting on college football and admitted it was "pretty fun".
He told the March issue of Esquire magazine: "I actually used to be a front for the largest national sports-betting syndicate in America...we were clearing like £484 402 in four weeks of college football.
"It was pretty fun. Then they caught on. The hypothesis had been that the house would just assume that I was a dumb actor with a lot of money who liked football."
Ashton also revealed he always knows when he has made a bad movie because his friends are honest about his work.
He said: "I know exactly what films I've done that fucking suck donkey. And I know the ones that are good, that people like.
"And I know it not because of the box office, because the box office is not going to tell you the truth.
"I know it because I have friends that don't hold back. They don't depend on me for money or employment. They're just friends. Friends tell the truth. My big thing is, Fail fast.
"If you're going to fuck up, get it over with."