The overall stock market as measured by the S&P 500 has soared just more than 10 percent since Election Day and prices are looking "pretty fully valued" at current levels, Vanguard founder Jack Bogle told CNBC on Monday.
"My own opinion is the market is pretty fully valued here. [But] I don't think in a highly risky way," Bogle said on "Squawk on the Street."
But Bogle did express concern about which measure of corporate earnings investors should be paying attention to.
"I think the important thing to watch is this big gap that we are seeing right now in operating earnings in the future compared to reported earnings in the past like GAAP earnings, generally accepted accounting principles," he said.
"If you look at GAAP earnings
"So is it 26 or is it 16? Or is it something in between?" he asked, though he did not provide an answer beyond saying that measuring the market by its price-earnings ratio shows it's "relatively expensive."
Bogle founded Valley Forge, Pennsylvania-based Vanguard in 1975. The fund group has $4 trillion in global assets under management, with more than 20 million investors in about 170 countries.