Tesla's winning streak is unlikely to last much longer, Bernstein analysts found after looking through historical data for what happens after large stocks doubled in under six months.
Bernstein analyzed 40 years of trading data, looking at stocks with market values over $20 billion. With Tesla shares up more than 100% in the last six months, the firm wanted to help give investors a better idea of where the stock was headed – even as Elon Musk's electric car maker is almost rising to new record high levels daily.
"The track record is mixed – on average, large caps that doubled in the last 6 months subsequently saw a forward 6-month absolute return of just 2.6%," Bernstein analyst Toni Sacconaghi wrote in a note to clients.
The firm excluded time periods of high growth — such as the tech bubble two decades ago or the recovery from the Great Recession — in analyzing stocks that double in under six months. On average, Bernstein found this happened three times a year.
Despite Bernstein's mediocre outlook, Tesla shares rose 7% in Tuesday trading to close at $547.20.
Bernstein also looked at both the technology and automotive sectors, since investors often count Tesla in one or both categories.
"Doublings have been most common in the tech sector, which accounted for 55% of all cases in the last 40 years," Sacconaghi said. "Importantly, it is extremely unusual to see a doubling occur in the autos and industrials sectors, which could explain why auto investors appear to be more surprised at Tesla's recent rise than tech investors."
Bernstein counted five instances of auto company stocks doubling in the past four decades, and two of those have been Tesla (2013 and currently). The three others were Ford and Daimler after the Great Recession, after both stocks neared bankruptcy, and Fiat Chrysler three years ago, when the company's strong performance combined with merger speculation to send the stock soaring.
The firm also noted that, overall, the next six months of a high-flying stock's performance "appears to track revenue revisions." Bernstein said companies that significantly revise revenue forecasts higher typically continue to perform well even after doubling, as both shares of Tesla and Nvidia have in recent years. Bernstein does not expect those upward revisions will happen this time, however.
"On net, we continue to believe near-term risk / reward is skewed to the downside for Tesla. We acknowledge it is difficult to call the top on a rocket ship ... but we note expectations for TSLA appear to be rising materially, while we remain cautious," Sacconaghi said.
Bernstein has a market-perform rating on Tesla with a $325 price target — 40% lower than the current price.
– CNBC's Michael Bloom contributed to this report.