S&P 500 Index

How the Index Is Built

S&P Dow Jones Indices decides on changes through an index committee. Size alone does not earn a place. A company must be based in the US and meet thresholds for market value and trading volume. It also needs positive earnings for the latest quarter and for the last four quarters combined. Each member is weighted by the market value of its freely tradable shares, known as float-adjusted market capitalization. The Dow Jones Industrial Average works differently and weights its 30 members by share price.

Some companies appear with two share classes, Alphabet for example with GOOGL and GOOG. The UCITS ETF behind the table above therefore held 504 positions on September 10, 2026.

How Concentrated the S&P 500 Is

On that date the ten largest positions made up 38.3% of the fund. Nvidia weighed 8.10%, Apple 7.35% and Microsoft 5.60%. Information technology was the largest sector at about 38%. When a few of these companies move sharply, the whole index shows it. The study US weight in the MSCI World looks at the same effect one level up, in the world index.

SPY, VOO and IVV

Three US-listed ETFs on the index are especially well known. The SPDR S&P 500 ETF Trust (SPY) launched in January 1993 as the first US ETF; the iShares Core S&P 500 ETF (IVV) and the Vanguard S&P 500 ETF (VOO) followed later. Private investors in the EU generally cannot buy them, because US-domiciled funds do not publish the key information document (KID) required under the PRIIPs regulation. The UCITS ETFs listed above follow the same index and are domiciled in Ireland. They differ in costs, fund size and in whether dividends are paid out or reinvested; the guides on ETF fees and distributing vs. accumulating ETFs explain both points.

What the Chart Shows

Instead of the cash index, the chart uses E-mini S&P 500 futures (ticker ES) from CME Group. They trade almost around the clock on weekdays, while the index is calculated only during New York trading hours. Every data point is a daily settlement of the front-month contract, with returns chained across contract changes. The gap between futures and index is usually small and reflects interest and expected dividends until expiry. The newest value is the settlement from the previous session.