The S&P 500 is not as diversified as you think.
Most people treat it as "the market" — a safe, broad, boring default. It's broad. Whether it's as diversified as its reputation suggests is a question worth actually checking.
For research and education. Not financial advice.
What it actually is
The S&P 500 tracks around 500 of the largest US-listed companies. Crucially, it is market-capitalisation weighted: the bigger the company, the larger its share of the index. It is not 500 equal slices — not remotely.
That weighting has a consequence people consistently underestimate. In recent years a small handful of the very largest technology companies have grown to represent a substantial share of the whole index. The precise figure moves, so go and check it rather than trusting a number from a website — but the structural point holds: when you buy "the market", a large part of what you are buying is a concentrated bet on a few mega-cap technology names.
That isn't necessarily bad. It is, however, very different from what most people believe they own, and the difference only becomes obvious in a drawdown.
SPY, VOO, VTI — what's the difference?
- SPY and VOO both track the S&P 500. They hold essentially the same companies. The differences are structural and cost-related, not about what's inside.
- VTI tracks the total US market — thousands of companies, including small and mid-caps. It sounds much broader, and it is. But because it's also cap-weighted, the same mega-caps still dominate the top of it. Owning both VOO and VTI gives you far less diversification than owning two funds suggests.
This is the single most common accidental duplication in retail portfolios — and it's worth understanding why.
This is a description, not a recommendation. We are not telling you to buy or avoid any index or fund — that depends on circumstances TRUE knows nothing about. We're telling you what's inside, because a surprising number of people don't know, and it's their money.
Frequently asked questions
Is the S&P 500 diversified?
It is broad — around 500 companies — but it is market-cap weighted, which means a handful of the largest technology companies carry a disproportionate share of the outcome. Broad and diversified are not the same thing.
What's the difference between SPY and VOO?
Both track the S&P 500 and hold essentially the same companies. The differences are structural and cost-related rather than about what's inside them.
Should I own the S&P 500?
We can't answer that, and we won't. Whether any investment suits you depends on your goals, time horizon and risk tolerance — a question for a qualified financial adviser, not a website.
See what you actually own.
Concentration, correlation and fund overlap — stated honestly.
For research and education. Not financial advice.