Since he entered politics, Donald Trump has been cutting opponents like a sushi knife through tuna. Some people like his caustic candor. Others wish he wore a muzzle. He’s raw. He’s bombastic. But he’s also great with money. At least, that’s what he claims. During his June candidacy speech he said, “I’m really rich…that’s the kind of thinking you need for this country.”

Some reports, however, say that Trump could be richer if he hadn’t thought at all. Karla Bowser, writing for MoneyTalks News, says Trump could have sold all of his real estate in 1982. If he had quit working and invested the proceeds in the S&P 500, he would be $10 billion richer than he is right now.

It’s a headline-catching story. But is it really true?

In 1982, the first year Forbes published its list of the wealthiest Americans, the magazine calculated Donald Trump’s net worth at $200 million. By 2014, Forbes said his wealth had jumped to $4.1 billion. That’s a compounding annual return of 9.9 per cent. But Trump cries foul.

He complains that Forbes downplays his wealth. According to Business Insider, he recently said his net worth is $8.7 billion. In 1999, Forbes said, "We love Donald. He returns our calls. He usually pays for lunch. He even estimates his own net worth. But no matter how hard we try, we just can't prove it."

Let’s assume that Forbes is wrong—and that Trump has the money he says he does. According to Timothy L. O’Brien’s book, TrumpNation: The Art of Being The Donald, Mr. Trump said he was worth $500 million in 1982, not the $200 million reported by Forbes. If we ignore Forbes’ data and base Trump’s wealth on his own figure ($8.7 billion) we find that his net worth has increased by an average compounding rate of 9.05 percent per year.

If Trump had invested that initial $500 million in Vanguard’s S&P 500 index fund, he would have compounded his money by 11.3 percent annually over 33 years. His $500 million would have grown to $17.11 billion. That’s $8.41 billion more than Trump says he has.

But this isn’t fair. Donald Trump couldn’t have invested $500 million in the S&P 500, sat on his butt, then reinvested all dividends. The guy needs to eat. His tastes are expensive. He owns, among other things, a private jet, a Rolls Royce and a blue Lamborghini.

So let’s give Trump a “salary.” In 1982, he could have redeemed $10 million from his S&P 500 index. That’s 2 percent of the $500 million that Donald Trump said he had. Inflation averaged 2.95 percent between 1982 and 2014. That means Trump’s $10 million would have had the buying power of $23.19 million today. According to Yahoo! Finance, that’s almost $14 million more than Timothy D. Cook, Apple’s CEO, earns each year. It’s $18.66 million more than Satya Nadella earns as Microsoft’s CEO.

If the S&P 500 averaged 11.3 percent per year, and if Trump sold 2 percent of his portfolio annually, he could have spent like a king while his wealth grew by a compounding average of 9.3 percent each year. This would have turned his $500 million into about $9.4 billion today. That’s $5.3 billion more than Forbes estimates. It’s $700 million more than Donald Trump says he has.

The growth of the U.S. index would have been kind to The Donald. If he sold just 2 percent of a $9.4 billion portfolio in 2015, his income for the year would be $188 million. Even Trump would have a tough time spending that.

So the seemingly impossible appears to be true. Donald Trump could have quit working in 1982. He could have invested his fortune in the S&P 500. He could have spent multiples more than most Fortune 500 CEOs. And he would be wealthier today than if he spent a career buying real estate, writing books, and serving as the boss on The Apprentice.

At a political rally in Phoenix, Arizona, Trump said, “I went to the Wharton School of Business…I’m like, a really smart person.” The Donald might be smart. But if you invest with index funds, you could be smarter.