The S&P 500 is having a banner year on paper. The benchmark index is up about 14% in 2026 and has repeatedly set record highs. But look underneath the headline number, and a very different picture emerges: more than four in ten companies in the index are actually down for the year.
That disconnect is the defining feature of this market. The gains are not being shared broadly. Instead, they are concentrated in a small circle of artificial intelligence and semiconductor giants, whose soaring valuations are doing the heavy lifting for the entire index.
What the numbers actually show
Data from London Stock Exchange Group, cited by Reuters, puts the split in stark terms. The median S&P 500 stock is up only about 4% this year — far below the index's 14% gain. More than 200 members are lower, and roughly a quarter are down 11% or more.
That gap between the average and the median is a classic sign of a top-heavy market. When a handful of very large companies drive the index, the average return can look strong even while most individual stocks lag. The median — the midpoint stock — tells you what a typical company is actually doing, and right now that is a much more modest story.
Market professionals watch this through a lens called "market breadth," which measures how many stocks are participating in a move. One common gauge is the share of companies trading above their 200-day moving average — a widely followed line that smooths out short-term noise and shows whether a stock is in a sustained uptrend. Fewer than half of S&P 500 companies are currently above that line, and the figure was just 40% a week ago, the lowest reading since May 2025.
Why breadth matters to your portfolio
For everyday investors, a narrow rally is not just a curiosity — it has practical consequences.
First, it means the index funds many people hold in retirement accounts may be more concentrated than they realise. Because the S&P 500 is weighted by market value, the biggest companies carry the most influence. When a few giants lead, a plain vanilla index fund becomes, in effect, a bet on those giants. If they stumble, the index can fall even if hundreds of smaller companies are doing fine.
Second, a narrow market can be more fragile. Broad rallies, where most sectors and stocks rise together, tend to be more durable because they reflect widespread economic strength. When gains rest on a small group, the index is more vulnerable to a shift in sentiment toward that group. Investors have already seen how quickly that can happen: doubts about AI spending have rattled chip stocks in Asia, as seen in recent pressure on Korean and Taiwanese chipmakers.
Third, it changes the conversation about diversification. A portfolio that looks diversified on the surface — say, a broad US index fund — may in practice be heavily exposed to the same AI theme through its largest holdings. Investors who want genuine balance may need to look beyond the headline index.
The bigger backdrop
This is not the first time markets have been led by a small group. In the late 1990s, technology and telecom stocks drove the index to extraordinary heights before a sharp reversal. More recently, the so-called "Magnificent Seven" mega-cap tech names have dominated returns for several years.
What makes the current setup notable is the scale of the divergence. A 14% index gain alongside a 4% median return is a wide spread, and it suggests that investors are paying a premium for exposure to the AI theme while treating much of the rest of the market with caution. That caution may reflect genuine concerns — slower growth in some sectors, the drag of higher interest rates on borrowing costs, or simply a preference for the perceived safety of dominant companies.
It also comes against a global backdrop where investors are weighing a mix of forces, from global yields and trade tensions weighing on Chinese equities to shifting expectations around inflation and central bank policy. In that environment, capital has tended to flow toward the largest, most liquid US names.
What investors should watch next
The key question is whether breadth improves or deteriorates from here. A few signposts are worth tracking:
- The 200-day moving average count. If more stocks climb back above this line, it would signal a healthier, broader uptrend. A further drop would reinforce the narrow-market narrative.
- Earnings from the AI leaders. Their results and guidance will heavily influence whether the concentration trade continues or unwinds.
- Rotation into laggards. If money starts moving into sectors that have been left behind — financials, industrials, healthcare — that would be a sign of broadening confidence.
- Interest rate expectations. Lower rates tend to help smaller, more indebted companies, which could narrow the gap.
None of this means the rally is about to end. It does mean that the index's headline gain is telling a simpler story than the one playing out across the market. For investors, the takeaway is to look past the number and ask a harder question: is my portfolio as diversified as I think it is?
