Skip to navigationSkip to main contentSkip to right columnADVERTISEMENTJared BlikreMon, June 8, 2026 at 7:48 PM GMT+2 3 min readMarvell Technology (MRVL) jumped about 13% Monday after getting invited into the S&P 500 (^GSPC), the kind of move that can force index funds to buy and traders to pile in ahead of them.The catch is that the edge usually comes early. After analyzing 1,926 S&P 500 additions going back to 1957, Yahoo Finance found that stocks tend to outperform before joining the index, then fall behind the market after they get in.For funds that track the S&P 500, a new member has to be bought. That creates a simple setup: Index funds need shares, hedge funds try to anticipate the buying, and the stocks getting added tend to be performing well already.For regular quarterly additions like Marvell's, the median stock beat the S&P 500 by 3.3% in the 25 trading days before joining the index.Median return over the market for scheduled S&P 500 additions, 25 trading days before entry · Norgate, S&P Dow Jones Indices, Yahoo Finance analysisThat history is what makes Marvell's move tricky. The chart suggests the cleanest index-driven edge often shows up before entry day — and Marvell has already captured a big piece of that move with nearly two weeks still to go before its June 22 inclusion.But the official entry date has not been the finish line. The picture gets less friendly after the stock officially joins, which is what this next chart shows.Median return over the market after scheduled S&P 500 additions, 2010–present · Norgate, S&P Dow Jones Indices, Yahoo Finance analysisThe chart does not suggest stocks that join the index are losing money outright. It measures performance against the S&P 500, meaning the stock's return minus the index's return over the same stretch.On that basis, the median addition trailed the index by about 1% after one quarter, about 2% after two quarters, and nearly 8% after one year. Nearly 60% of additions were trailing the S&P 500's performance one year later.The pattern has changed over time.Yahoo Finance analysis found that before 1990, the S&P 500 addition effect was barely visible. From 1990 through 2009, it became much stronger as passive investing grew and index demand became a bigger force in the market.Since 2010, the effect has not disappeared. It has moved earlier. As the trade became better known, hedge funds and other investors had more reason to guess the next index reshuffles and front-run the official rebalance, pulling forward more of the buying pressure.That still does not make index inclusion destiny.Palantir (PLTR) is the monster upside example, while Super Micro Computer (SMCI), Netflix (NFLX), and PENN Entertainment (PENN) show how fundamentals can swamp the index effect after entry.Selected one-year returns over the market after joining the S&P 500 · Norgate, S&P Dow Jones Indices, Yahoo Finance analysisThat is the next test for Marvell.The S&P 500 invite can create demand into its June 22 entry date. After that, the stock has to prove whether the index bump was a starting point — or just the easy part of the move.Terms and Privacy PolicyPrivacy & Cookie SettingsMore Info