In October, the S&P 500 Equal Weight Index beat the cap-weighted S&P 500 by almost six percentage points, after trailing it by 4.6 points in September. That 10 point swing was the largest since the index launched in 2003. Under the hood, it was a rotation out of the AI ecosystem and into the rest of the market. And for investors, a timely reminder of what equal weighting is and what it is not.
What is an equal-weighted index?
A market-cap-weighted index sets each constituent’s weight in proportion to its market capitalisation, so the largest companies drive returns. An equal-weighted index gives every constituent the same weight at each rebalance and resets to that target on a fixed schedule, typically quarterly. Between rebalances, weights drift with prices. At each rebalance the methodology trims recent winners and tops up laggards, making it systematically contrarian.
Why equal weight is gaining traction
Equal weighting has gained ground largely because cap-weighted concentration has reached record levels, driven primarily by IT and AI-adjacent sectors. The top 10 stocks in the S&P 500 hit 40.7% of the index in 2025, after sitting between roughly 18% and 23% for most of 1990 to 2015.
Against that backdrop, the diversification case is easy to see. The Magnificent Seven make up roughly a third of the cap-weighted index but only around 1.4% of its equal-weight counterpart, and the ten largest equal-weight holdings account for around 3.2% of the index. Single-name risk is negligible and sector exposure is far broader.
History also adds a mean-reversion argument. In the late 90s dot-com bubble, internet stocks swelled to outsized weights in the cap-weighted S&P 500. When the bubble popped in 2001, the equal weight index outperformed for seven consecutive years, and over the following decade it returned 65% while the traditional cap-weighted S&P 500 fell by 9% to 10%. Investors who worry that today’s concentration could unwind in a similar way likely view equal weighting as a structural hedge against this scenario.=
The drawbacks
Equal weighting, however, is by no means a silver bullet. It deliberately underweights the largest winners, so it lags when market leadership is narrow, as it was for much of the past decade. Part of the explanation is that equal weight is not a “safer” S&P 500 but an active tilt towards smaller companies and an anti-momentum bet.
Implementation is the second cost. Tema ETFs estimates that the equal-weight S&P 500 averaged nearly 6% quarterly turnover over seven quarters between mid-2004 and early-2006, more than six times that of the cap-weighted index. Equal-weight ETFs also typically charge around 0.20% against 0.03% to 0.07% for the cheapest cap-weighted S&P 500 funds.
Beyond the binary choice
Equal weight is one end of a spectrum. Capped market-cap weighting, historical-average weighting, factor-tilted equal weight, and blends of cap-weighted and equal-weighted sleeves all aim to balance concentration, tracking error and turnover differently. The right answer depends on the investor’s objective and tolerance for benchmark deviation.
PANTA helps asset managers design, backtest and compare equal-weight and other alternative-weighting methodologies, so they can quantify turnover, tracking error and sector drift before launching a product, and iterate on rebalancing rules, caps and constituent screens.
Conclusion
October’s reversal will not settle the debate between equal and cap weighting. It does, however, show that an index’s weighting scheme is a meaningful investment decision, and one that can be designed deliberately to realise different outcomes.