The market may be rallying on hopes for economic improvement, but the long-term growth outlook doesn't look so sunny, investment legend Jack Bogle said Tuesday.
"I don't feel super confident," the Vanguard founder told CNBC's "Squawk on the Street," saying that he prefers to look at the market over 10-year intervals.
"In 10 years, looks like our GDP might grow at 2 percent, if we're lucky. And sooner or later, the link between GDP, gross domestic product and corporate profits is about 0.98 [percent]. So I look for a slowing in profit growth," Bogle said.
With the way the economy is structured today, Bogle said it would a struggle to reach the White House's goals of 3 to 3.5 percent growth.
The week after Donald Trump's inauguration, Bogle told CNBC there were seven financial reforms he hoped the new administration would embrace, including bringing back Glass-Steagall and supporting transparency and disclosure standards.
On Tuesday, Bogle also spoke of the benefits of indexing, or adjusting asset weights in a portfolio so that its performance matches that of an index.
One way investors do so is by investing in index funds such as those offered by Bogle's Vanguard, which started the first index fund for individual investors in 1976.
"The reason indexing has done so well is because it gives the investor a fair share, his or her fair share, of whatever market returns we get. And that's all there is to it," Bogle said, touting the investment strategy's low-cost, low-turnover rate, and high tax efficiency.
Referring to the 21st anniversary of his heart transplant, Bogle said: "So here I am on my 21st heart birthday, celebrating that miracle, but also celebrating the revolution that indexing is bringing to the financial markets."