Joshua said: "They said I'm going to be a billionaire boxer? Is that before or after tax?
"What would I have to make before tax to be a billionaire boxer? Is that gross or net?
"What would I spend it on? Properties, then you have to leave some in the bank.
"Pensions, ISAs and bonds, that kind of stuff. And holidays, you've got to have holidays."
Joshua's promoter Eddie Hearn says his boxer's humble lifestyle and out-of-ring appeal to the mainstream will help to safeguard and grow his earnings.
Unlike Iron Mike Tyson, who threw away millions, and fellow British great David Haye, who according to upcoming opponent Tony Bellew is only making a comeback because he's skint, Joshua has a wise head on his giant shoulders and a determination to stay grounded.
Hearn said: "He's had and good year but a billion is a lot of money.
"He is earning phenomenal money both in and out the ring and this is the biggest fight in boxing history. It's also the biggest financially.
"To hit those numbers you need to be on US TV as well, and you can earn that money.
"He's also the perfect ambassador for any brand and that is why he has so many corporate sponsors."
Many boxing fans still hold Tyson Fury up as the man-to-beat in world boxing after he ended Klitschko's decade-long reign of dominance.
But Fury's mental instability and drug related issues have caused him to be stripped of his belts and cast aside, just months after he climbed to the top of the boxing world.
And sadly, for Joshua's bank balance and the curiosity of fans, Hearn believes Fury is still far from a return to the ring as his most pressing battle right now is with himself.
Hearn said: "He's a long way off even returning to the gym.
"He has got so much work to do even to just get in shape to have a training camp.
"I don't think any return to boxing is imminent. But I think he will return to boxing and I hope he does."
