A broad look at the 6.5 million customer accounts at TD Ameritrade indicates that retail investors are "pretty fully invested" in stocks, the online brokerage's CEO said Thursday.
Fred Tomczyk cited several signs of this: margin loans at high levels, client cash at low levels and account holders at the firm logging in frequently. "It's usually a good indication that people are very engaged in the markets and watching their investments closely," he said on CNBC's "Squawk Box."
But Tomczyk acknowledged the potential pitfalls of these trends and what they may portend for stocks. "I wouldn't be surprised if we have a correction here. We've had six [or] 6½ years of up markets here."
The Dow Jones industrial average and the S&P 500 were relatively flat on the year as of Wednesday's closing. "I think last year it wasn't an overly strong market. This year it hasn't been an overly strong market," Tomczyk said. "I think it's all going to depend on what the data tells us about the U.S. economy in the next three to six months."
Many economists are expecting a pickup in growth in the second half of the year, after the government on Wednesday reported that first-quarter gross domestic product grew at a lower-than-expected 0.2 percent. The economy advanced 2.2 percent in the fourth quarter and 5 percent in the third quarter of 2014.
In a policy statement Wednesday, the Fed played down the soft economic growth and removed all calendar references to when an interest rate hike may be coming.
Liftoff in June seems to be pretty much out, with September seen as the most likely month for the first rate increase in nearly a decade. But Tomczyk believes the Fed won't move until later. "What the forward [yield] curve would tell you right now [is] short term rates aren't going to move until December."
Earlier on "Squawk Box," UBS economist Drew Matus argued for a June move. "They had June lined up in their sights as of March."
"I think everything would be functioning a lot better now," if the Fed didn't back off, he said.