He was ridiculed in 1999 for predicting Dow 40000. Look who’s laughing now.

The caps were a gift for a celebration that was 25 years in the making.

Elias, who is 79 years old and lives in Williamsville, N.Y., predicted in his 1999 book, “Dow 40,000: Strategies for Profiting from the Greatest Bull Market in History," that the index would cross the milestone by 2016. He missed the mark by eight years, but the forecast was better late than never, he said in an interview.

The 30-stock index charged past 40000 in intraday trading for the first time May 16—and then closed above the mark the following day. The benchmark has since pulled back, but it has risen about 4% this year and has more than doubled from its pandemic-era low in March 2020.

Elias’s prediction turned out to be optimistic in part because he, like almost everyone else, didn’t see major turning points in advance, in this case the 2000 dot-com bust and the 2008 financial crisis that hammered stock returns for significant periods.

That led to years of mockery online. The Dow fell about 30% between January 2000 and September 2001 to a low of 8235.81 after the Internet bubble popped. Then in March 2009, it tumbled to as low as 6547.05 following the collapse of Lehman Brothers and the government-sponsored bailouts of other lenders.

One reviewer on Amazon.com wrote of the book on March 7, 2009: “Makes a great doorstop! or paperweight. Might be good for squashing a cockroach. The pages could be torn out and used to light your fireplace. Lots of good uses yet for this one!"

The book is available for sale in used condition on Amazon at prices from $3 to $97.64. It has a 4.1 rating based on 16 reviews.

Elias isn’t the only one who has attempted to predict the timing of major market milestones and come up short. The book “Dow 36,000: The New Strategy for Profiting from the Coming Rise in the Stock Market" by James Glassman and Kevin Hassett, also published in 1999, predicted the Dow would cross that threshold quickly. It didn’t happen until 2021.

Elias is already out with a new hot take: He expects the Dow to hit 67000 in the next 10 years.

“I’m 100% confident," he said. “And artificial intelligence is one of the reasons why I feel that way."

Elias celebrated the recent milestone with his wife and one of his daughters, who brought over bagels, lox and cream cheese, his favorite foods for breakfast.

The Dow 40000 hats were a gift from Bob Fischer, a friend of 20 years.

Elias and Fischer ran rival investment shops in the Rochester, N.Y., area with similar investing styles. The two often competed for clients.

“As the Dow 40k got closer, I always had it on my radar to do that—to send a cap," said Fischer. “I’m a big cap guy."

Elias is wearing his cap everywhere. His wife and daughter won’t be caught dead in them.

“I don’t wear hats," wife Barbara Elias said.

Here are some of Elias’s other forecasts from 1999 and how they have fared:

Elias predicted Microsoft and Intel would join the Dow and lead the index higher. Both stocks were added to the index the year his book came out. Microsoft is now the most valuable U.S. company and made the second-biggest point contribution to the Dow’s rise from 30000 in November 2020.

He said domestic stocks would outpace their global peers. Since the end of 1998, the Dow has added more than 325%. Japan’s Nikkei 225 is up about 180%, while the Stoxx Europe 600 has advanced more than 85% and the Hang Seng Index has climbed roughly 90%.

Elias estimated Latin America would enjoy rapid growth over the next 20 years. Economies such as Mexico, Venezuela, Brazil, Argentina, Chile, Peru and Colombia have been mired in recession or other crises, significantly hindering their growth.

Write to Hardika Singh at hardika.singh@wsj.com