It's been quite a month for @Jack.
Square, the payments company that Dorsey launched three years later, has performed even better, surging nearly 24 percent for the month to a record $58.90 as of Thursday morning.
Dorsey has been as much a beneficiary as anyone. His stake in Square has jumped by $668 million this month, and his Twitter shares have appreciated by $65 million.
As May comes to an end, Square is worth $23.6 billion, not far behind Twitter's $26 billion stock market value. After years of skepticism, Wall Street has apparently come around to the idea of the 41-year-old Dorsey running two publicly traded companies at the same time.
When Dorsey took over Twitter from Dick Costolo in 2015, it was supposed to be temporary. At the time, Dorsey had his hands full with Square, which was preparing for its stock market debut and was having trouble justifying its private market valuation to prospective investors.
Twitter's board couldn't agree on anyone else, so Dorsey was given the full-time gig at Twitter just a month before Square's IPO. Analysts were relieved to see the process come to an end, but had plenty of concerns.
"As a product guy, Dorsey is a good fit, although we thought an outsider was the best option," wrote Evan Wilson of Pacific Crest Securities. Analysts at JMP Securities wrote that, "While it remains to be seen how well new CEO Dorsey can manage both Twitter and Square, we believe he will be most focused on Twitter's product and making it easy to use."
Investors who stuck with Dorsey have made a bunch of money, particularly in the past year. Twitter shares have climbed 88 percent over the last 12 months, outperforming all of the most valuable tech companies. Over that same stretch, Square is up 154 percent.
Twitter was catapulted recently by a better-than-expected earnings report. In late April, Twitter recorded its second straight profitable quarter, with earnings and revenue that beat analysts' estimates. Video ads were a big driver of sales growth, and the company also lured advertisers internationally, especially from China and Japan.
Square issued a disappointing earnings forecast after the bell on May 2, but the shares went up the next day anyway. Heading into Thursday, Square's stock had gained on 16 of the 20 trading days in the month, one more than Twitter.
Gross payment volume increased 31 percent to $17.8 billion in the fiscal first quarter, as merchants continued to shift from older payment systems to Square's modernized point-of-sale terminals.
"SQ has the Big MO (Momentum)," Joseph Foresi, an analyst at Cantor Fitzgerald, titled a report after the company's results. "We expect rapid growth to continue and foresee further margin expansion going forward, driving stock performance," he wrote.