Citi isn’t the only one with a fat finger problem

The 45-year-old electrician was rushing one day last year to jump in on an investing trend he’d read about on Reddit. In his haste, he entered the wrong ticker symbol.

“A biotech company was having a little bit of a squeeze," he said. “I tried to jump in right at the end of the day, and I fat fingered the wrong ticker."

The blunder left Robinson holding $500 worth of shares in shipping company Imperial Petroleum, whose ticker symbol is IMPP. He had meant to buy shares of Immutep, which specializes in cancer immunotherapy and goes by IMMP.

Erroneous stock purchases like Robinson’s comprise less than 1% of all trades, but that represents a whopping $3.5 billion a day based on current trading volumes, according to Rutgers University finance professors Vadim Balashov and Andrei Nikiforov. They estimate more than half of stocks that trade on the Nasdaq and the New York Stock Exchange at any given time have tickers that are similar to others, making them ripe for confusion.

Mistakes aren’t always apparent right away. Robinson didn’t discover his error until the following morning, when he saw that Immutep’s shares had gone up by about a dollar, yet his holdings hadn’t budged.

“It dawned on me I was losing money on a trade everyone else was making money on," he said.

Robinson stuck with Imperial in hopes that it would turn out to be a moneymaker. That gamble paid off; the stock is up 56% year to date, while Immutep is up 25%. “I got lucky," he said. Still, he’s changed how he goes about investing.

“I’m slower following the Reddit hiveminds into trades, and if I do, I’m exercising more caution," he said. “I’m double-checking myself and triple-checking the sentiment."

In the Citi case, an unnamed trader’s “inputting error" led to the sale of $1.4 billion in equities, prompting a “flash crash" in European stocks. U.K. regulators said in a report that the trader was able to override alerts, due to poorly designed internal controls.

For everyday investors, racing to beat the clock is a common reason cited for mistakes, as are old-fashioned typos. Others blame companies for choosing stock symbols that sow confusion. Consider that automaker Ford Motor trades under F—not FORD, which is the ticker for Forward Industries, a design and manufacturing company.

Ticker mix-ups date back decades, the Rutgers professors say. When JP Morgan merged with Chase Manhattan Bank in 2000, for example, the new company’s ticker symbol became JPM. Some investors confused it with JPM Co., a manufacturer that traded under JPMX. (That stock symbol has since been retired).

In June 2020, Evgenii Markin decided to buy $10,000 of Tesla shares. It wasn’t until later that he realized that he’d become an accidental investor in biotech company Tiziana Life Sciences. The stocks, which trade under the symbols TSLA and TLSA, respectively, were initially rising at about the same rate.

“It was a coincidence," said the 29-year-old real-estate professional in Staten Island, N.Y. “So I was happy with this result."

After about two months, Markin’s error didn’t seem so fortunate. By then, Tesla shares had doubled in value. Tiziana stock had gained but not nearly as much.

“I tried to console myself with the fact that Tiziana was also a relevant investment," said Markin. “It could have been worse."

As Zoom’s video meetings surged in popularity early in the pandemic, investors confused the company’s ZM ticker with Zoom Technologies’ ZOOM. It was enough of a problem that the Securities and Exchange Commission suspended trading on the latter, citing “the public interest and the protection of investors."

When Elon Musk changed Twitter’s name to X last July, shares of U.S. Steel got a bump. The Pittsburgh-based manufacturer’s ticker symbol is also the letter X.

Brian Meiggs, 33, has been day trading since he was in college and runs a personal-finance website called My Millennial Guide. Early on in the meme-stock craze of 2021, he decided to invest about $50,000 in GameStop, whose ticker is GME. Instead, he ended up holding shares of Globus Medical, a biotechnology company that trades under GMED.

It was 3:54 p.m., and Meiggs, who lives in northern Virginia, said he was rushing to take advantage of the videogame retailer’s rapidly rising stock price minutes before the market closed.

Meiggs was trying out a new investing app and figured that one of his fingers must have inadvertently touched the letter D on the keypad just before he hit “buy." He noticed the error immediately. It was too late to stop the transaction, but he had enough time left to sell what he’d just bought. It cost him about $150; Globus Medical’s share price had fallen by 17 cents during the few seconds in between.

“It’s an easy mistake to make if you’re on a new platform and kind of rushing," said Meiggs. “I’m more meticulous now."

Write to Sarah E. Needleman at Sarah.Needleman@wsj.com