Week 17 Day 3: The S&P 500: 500 Companies Working for You

When you buy an S&P 500 index fund, you own Apple, Microsoft, Amazon, Google, Berkshire Hathaway, Johnson & Johnson, and 494 other companies. You do not need to pick which one will win. You own all of them. If one fails, the others carry the load. The index rebalances itself as companies grow and shrink.

The S&P 500 is not literally the 500 largest U.S. companies. It is curated by a committee at S&P Dow Jones Indices that selects companies based on market cap, profitability, liquidity, and sector representation. This active curation means it automatically adds rising stars and removes fading companies. Tesla was added in December 2020 after meeting profitability criteria. Companies that decline enough are removed and replaced. The index is market-cap weighted, meaning the largest companies have the biggest impact. As of 2024, the top 10 stocks represent about 35% of the index -- a concentration risk worth noting. Performance: $10,000 invested in the S&P 500 in 1994 (30 years ago) is worth approximately $200,000 including dividends. $10,000 invested in 1984 (40 years ago): approximately $850,000. The key: you had to stay invested through every crash, correction, and panic. The S&P 500 has recovered from every single decline in history. The average time from a 20%+ decline to full recovery: about 2 years.

The S&P 500's dominance as the default equity investment deserves scrutiny. The index's market-cap weighting creates a momentum bias: as a stock's price rises, its weight increases, automatically buying more of winners. This works spectacularly during trends (the FAANG-driven 2015-2024 era) but concentrates risk. The 'Magnificent Seven' (Apple, Microsoft, Nvidia, Amazon, Alphabet, Meta, Tesla) represented approximately 30% of the index by late 2024 -- concentration levels not seen since the early 1970s 'Nifty Fifty' era, which ended with a severe two-year bear market. Alternatives for those concerned about concentration: VTI/ITOT (total U.S. market, adds mid and small-cap), RSP (equal-weighted S&P 500, each stock at 0.2%), VXUS (international ex-U.S. for geographic diversification). Research by Arnott, Hsu, and Moore (2005) on fundamentally-weighted indices showed that weighting by earnings, book value, or revenue rather than market cap produced approximately 2% annual excess return over traditional cap-weighted indices from 1962-2004, primarily by avoiding overweighting overvalued stocks.