The Vanguard S&P 500 Index ETF Just Became the Second ETF to Surpass $1 Trillion in Assets

The headline news is that Vanguard S&P 500 Index ETF (NYSEMKT:VOO) has surpassed $1 trillion in assets. That's a big number, but what does it really mean for the exchange-traded fund (ETF)? Here's a look at how Vanguard S&P 500 Index ETF got so big and what investors really need to care about when looking at this ETF. (Hint: The size of the ETF isn't what's most important.)

What is the S&P 500 index?

Before getting to Vanguard S&P 500 Index ETF, you need to know about the S&P 500 index (SNPINDEX:^GSPC). The S&P 500 index is meant to track the broader U.S. economy. It contains roughly 500 stocks selected by a committee. The selected companies are generally large and economically important. A market-cap-weighted system is used, so the largest companies have the greatest impact on the index's performance, both on the upside and the downside.

Generally speaking, the S&P 500 has become the de facto representation of "the market." It is actually a fairly well-constructed index, though the market-cap-weighted approach often leads to unbalanced sector weightings. For example, today's strong technology sector has pushed this single sector to 35% of the index, nearly three times the size of the next closest sector (financials at 12%). The lofty valuations in the tech sector, meanwhile, have pushed the S&P 500's average price-to-earnings ratio to a fairly high 27.4x.

How did Vanguard S&P 500 Index ETF get so big?

Vanguard S&P 500 Index ETF's $1 trillion in assets came from two places. First, the S&P 500 index has been rising for years, boosting the value of the assets already in the ETF. Second, investors have been buying new shares of the ETF. Through the first five months of 2026, Vanguard S&P 500 Index ETF was the number one draw for investor capital in the ETF sector. It attracted $66 billion in that span, beating the $36 billion raised by the SPDR S&P 500 ETF (NYSEMKT:SPY).

The big reason is likely Vanguard S&P 500 Index ETF's 0.03% expense ratio, which is a third of the 0.09% charged by SPDR S&P 500 ETF. Since these two ETFs basically do the exact same thing, picking the cheaper option makes sense.

Does Vanguard S&P 500 Index ETF's size matter?

The way ETF shares are created is fairly complex. To simplify, an intermediary provides Vanguard with the basket of stocks included in the index, and Vanguard then issues new ETF shares. Those ETF shares exist until an intermediary asks Vanguard to break them up, at which point Vanguard gives the basket of stocks to the intermediary in return for the ETF shares.

Since the ETF isn't actively picking stocks, there's no need to worry about an asset manager being unable to find investments for the cash. And because of the way ETF shares are created, there's no need to worry about the ETF being a forced seller of stock in a bear market. So Vanguard S&P 500 Index ETF having $1 trillion in assets really isn't a big deal from an investment standpoint.

Worry about Vanguard S&P 500 Index ETF’s valuation

That said, if you are considering buying Vanguard S&P 500 Index ETF or own it, you might want to watch the valuation. As noted, the index is being driven higher by a small number of large technology companies, which has pushed the average P/E ratio to a fairly high 27.4x. The S&P 500 is, in fact, trading near all-time highs despite geopolitical conflicts, rapid inflation, and recession fears. Tracking "the market" is a good plan, generally speaking, but that market looks richly valued right now.

Reuben Gregg Brewer has no position in any of the stocks mentioned. The Motley Fool has positions in and recommends Vanguard S&P 500 ETF. The Motley Fool has a disclosure policy.