Investing in the S&P500
The is the most popular index in the world, and buying it through an is often presented as the simplest way to across the US . But depends on how spread out that ownership actually is. As of mid June 2026, it is far less spread out than most people assume.
How concentrated is the index, really
The has a combined of roughly $57.6 trillion across all 500 companies. NVIDIA (NVDA) alone makes up 7% of that total. That is more than entire like energy or utilities combined. Apple (AAPL) follows at 6%, Microsoft (MSFT) at 5%. Just three companies account for around 18% of the entire index.
Widen the lens to the Magnificent Seven (NVIDIA, Apple, Microsoft, Amazon (AMZN), Alphabet (GOOGL), Meta (META), and Tesla (TSLA)) and the picture sharpens further. As of early June 2026, these seven companies have a combined of $22.7 trillion. That is roughly one third of the entire 's value. Seven companies, out of five hundred.
This is what people mean when they call the . When someone buys a broad US expecting wide , a large share of what they actually own is concentrated in a handful of technology companies. Returns increasingly depend on how those few companies perform.
Why concentration matters for valuation
Concentration on its own is not necessarily a problem. It only becomes one if the companies driving that concentration are priced very differently from the rest of the market.
This is where ratios become useful. A company's ratio shows how many years of current profit it would take to earn back the price paid for the . When a small handful of companies trade at much higher ratios than the rest of the index, and those same companies make up a third of the index's value, the average valuation of the entire starts to reflect the expectations placed on just a few businesses. Not the market as a whole.
The also trades at a of roughly 3.5x, while , particularly around AI infrastructure, continues to rise sharply. A rising ratio alongside rising is a sign that investors are paying more per dollar of today, partly on the expectation that this spending will turn into future . Whether that growth materialises is the actual bet being made.
What to make of it
None of this means the is a bad investment, or that a correction is imminent. has happened before, and the index has historically provided broad market exposure even through periods where a handful of companies dominated returns. What it does mean is that buying the market today is not quite the same diversified bet it was a decade ago.
Predictions of a bubble bursting show up in financial media constantly, in good markets and bad, and they are notoriously difficult to time correctly even when eventually proven right. Rather than trying to predict the top, the more useful exercise is understanding what you actually own when you buy an , how concentrated it has become, and what assumptions about future growth are already priced into it.