Stop Calling It Passive: The Index Is an Active Bet

Open any S&P 500 index fund factsheet in April 2026. The top seven holdings sit at roughly 34% of the portfolio. Seven names out of five hundred carry a third of the exposure. We are supposed to call this passive. It is not. It is an active bet on seven stocks outsourced to a rules committee. The label matters less than the math, but the label is doing a lot of marketing work.

The word “passive” is doing marketing work

The word implies absence of decision. You are not choosing stocks. You are accepting the market. That framing obscures the actual decisions embedded in every cap-weighted index fund.

An investor in SPY or VOO in April 2026 is implicitly betting that seven AI-adjacent companies will continue to earn the multiples that got them to roughly 34% of index weight, per the S&P 500 factsheet. That is not absence of decision. That is a very specific tactical view on sector concentration, just one the investor did not knowingly make.

What the S&P index committee actually does

The S&P Dow Jones Indices committee decides which companies enter the S&P 500. The criteria are public: market cap thresholds, liquidity, positive earnings in the most recent quarter and trailing four quarters, and US domicile. The judgment is not mechanical.

Tesla’s December 2020 addition is the most-cited example. Tesla met size and liquidity criteria in 2019. The committee delayed inclusion roughly 18 months. When TSLA joined December 21, 2020, it was the largest single addition in index history. That decision was discretionary. It was also consequential for every passive investor who owned SPY.

Float adjustment, sector rebalancing, reconstitution timing, all of these are active choices embedded in a product marketed as mechanical.

Cap-weighting is a momentum factor

The deeper point. Market-cap weighting is itself an active weighting scheme. It overweights whatever has recently outperformed. When a stock doubles, its index weight doubles. When it halves, its weight halves. That is, by construction, a momentum strategy.

AQR’s Cliff Asness has written extensively about this, including in The Siren Song of Factor Timing. Momentum as a factor is real, persistent, and compensated over long periods. That is fine. The issue is not that momentum works. The issue is that cap-weighted index fund holders are running a momentum tilt without knowing they are running a momentum tilt.

Research Affiliates and Rob Arnott have made this critique for two decades through their fundamental-weighted index work. The critique is not “indexing is bad.” The critique is that the label “passive” is misleading about what a cap-weighted fund actually does.

RSP vs SPY, the equal-weight comparison

The test case is Invesco’s S&P 500 Equal Weight ETF (RSP). Same 500 stocks. Different weighting. Every name gets 0.2% of the portfolio at quarterly rebalance.

Rolling 10-year relative performance of RSP vs SPY tells the regime story. Per S&P DJI factsheets:

• 2001-2011: RSP ahead by roughly 150 basis points per year. The post-dot-com period rewarded breadth.
• 2015-2025: SPY ahead by roughly 280 basis points per year. Concentration paid.

Two eleven-year windows. Two opposite results. That is not noise. That is regime. The investor in SPY in 2015 was making a momentum bet that worked. The investor in SPY in 2001 was making a momentum bet that did not. Neither was passive.

What Bogle actually advocated

Jack Bogle’s original Common Sense on Mutual Funds made the case for low-cost, broad-market index investing. The specific product he championed in the 1970s was the Vanguard 500 Index Fund, which is cap-weighted. But the argument was about minimizing fees and maximizing breadth, not about cap-weighting as a principle.

Late-career Bogle, in a 2019 Wall Street Journal op-ed, warned about index fund concentration reaching systemic proportions. He saw the label drifting from what he had meant by it.

If you want passive, here is what that could mean

If “passive” means “accept the market without taking a view,” the honest options are not just cap-weighted SPY or VOO. They are:

• Total market funds like VTI, which hold approximately 3,700 stocks and dilute the Mag 7 concentration somewhat. Also cap-weighted, but broader.
• Equal-weight funds like RSP. Mechanical rebalance. No judgment about which names deserve more weight.
• Fundamental-weight funds like RAFI-based products. Weight by sales, book value, cash flow, and dividends rather than price. Mean-reverting by construction.

Each has tradeoffs. Equal-weight has higher turnover and modestly higher expense ratios. Fundamental weighting trails in momentum regimes. Total market is barely different from SPY at the top. The point is not that one is right. The point is that “passive” as a concept requires picking one of these, and that pick is an active decision.

The concentration check

The Herfindahl-Hirschman Index measures concentration. Ned Davis Research and Research Affiliates have published index-level HHI work showing S&P 500 concentration in April 2026 near the highest level since 1965. The SPIVA 2025 scorecard shows active managers still underperforming cap-weighted benchmarks in most categories, but the margin is narrowing in large-cap where concentration matters most.

In our view, the label matters less than knowing the bet

Cap-weighted indexing has delivered strong after-cost returns for decades. Morningstar’s Active/Passive Barometer documents that clearly. This is not an argument against owning index funds. This is an argument against calling them passive without understanding what you own.

You own seven stocks at 34% weight. You own whatever the S&P committee decides belongs in the club. You own a momentum factor tilt by construction. If that is what you want, own it with eyes open. If it is not, there are other ways to implement broad equity exposure that deserve the “passive” label more honestly than cap-weighted SPY does.

Index funds versus actively managed funds remains the right conversation for cost and tax efficiency. The label “passive” is the conversation that needs revising.

Past performance is not indicative of future results.

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Ferrante Capital LLC is a registered investment adviser. Information presented is for educational purposes only and does not constitute investment advice, a solicitation, or a recommendation to buy or sell any security. All investing involves risk, including the possible loss of principal.

FC and its principals may hold positions in SPY. This analysis is for educational purposes only and does not constitute a recommendation to buy, sell, or hold any security.

Forward-looking statements reflect Ferrante Capital’s current analysis and involve assumptions and estimates. Actual results may differ materially. Past performance is not indicative of future results.

Please consult a qualified financial professional before making investment decisions.