Five Stocks Drove 93% of the S&P 500's Gains: Why Narrow Markets Are Risky

Five giant tech stocks drove 93% of the S&P 500's gains since late July, according to MarketWatch.

The S&P 500 tracks 500 large U.S. companies, weighted by size, or market capitalization. Breadth, a measure of how many stocks join a rally, was thin. The other 495 companies together added just 7% to the move.

That narrow rally came after a choppy run. The index closed at 7,798.99 on Aug. 13, up 0.65% to a new record close, according to Reuters. Earlier it had posted a ninth straight weekly gain, rising 1.4% in just four trading sessions, according to Investopedia. In between, the Dow Jones Industrial Average dropped 953.33 points, or 1.9%, to 49,918.78, according to MarketWatch.

For scale, a fall in the S&P 500 to 5,400 would be a 23% drop from its recent peak, according to MarketWatch. A 20% drop is the usual line for calling it a bear market.

The broader context here is how a size-weighted index can hide weakness. When the biggest companies carry the most weight, five names can pull the index higher even if most stocks are flat or down. The index rises, but measures that give each stock an equal vote look much weaker, and single stocks drive more of the risk.

In my view, that changes how to read a pullback. When five stocks supply 93% of the gain since late July, the index takes on their risks. A bad earnings report, a lower valuation, or sudden selling hits the whole benchmark. Owning the index looks diversified on paper, but not in practice.

Looking at what this means for portfolios, there is a tight trade-off. Sticking close to the index captures the run but also the fall if leaders slip. Avoiding those five cuts that risk but creates a different one: lagging badly if they keep climbing. Tools like index insurance or holding less stock help with a broad fall, not with a shift where leaders stall and the rest still goes nowhere.

When it comes to liquidity, crowded trades can add to the swing. When many investors pile into the same leaders and use options and trend-following strategies, gains can look calm on the way up and turn sharp on the way out, as dealers and funds adjust together. The market can seem steady until selling in the leaders forces a quick repricing.

Stepping back, none of this tells us if the rally continues. Narrow markets can last, especially if profits keep flowing to the biggest companies. What is clear is the condition: for the index to keep rising, those five have to keep delivering. A broader rally would need the other 495 to pick up the slack, and that has not shown up in the numbers since late July.