Same 500 stocks, different outcome — equal weight vs cap weight
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A weighting rule is not bookkeeping — it is the strategy. That is why the same basket can produce different results.
The weighting rule is the strategy
Most people read a fund by asking what it holds. But even with an identical holdings list, how much goes into each name changes returns substantially.
The two common answers are market-cap weighting and equal weighting. The first gives bigger companies bigger slices; the second splits evenly regardless of size.
In a 500-stock index, equal weighting puts 0.2% in each name. Cap weighting can put over 7% in the largest and 0.01% in the smallest.
Cap weight: winners get more, automatically
A cap-weighted fund lets winners grow their own weight without any trading. A rising price means a larger market cap, which means a larger share of the index.
That is a genuine advantage. Capital rides compounding businesses automatically, and low turnover keeps trading costs and fees down. It is the most efficient way to simply own the index.
It is also the risk. When a handful of large caps lead for years, a nominally 500-stock fund ends up with a third or more in its top ten. A diversified label wrapped around a concentrated position.
Equal weight: sell the winners, buy the laggards
Equal weights do not hold themselves. Risers drift heavier, so the fund rebalances quarterly — trimming what ran, adding what lagged, restoring the even split.
The rule is contrarian by construction. Small constituents get the same slice as giants, so the fund takes on a mid- and small-cap character and the influence of a few megacaps shrinks.
The price is cost. Scheduled rebalancing raises turnover, and expense ratios generally run above the cap-weighted equivalent. Buying less liquid names up to a full weight adds friction too.
When they diverge, and what to check
When a few large caps lead the market, cap weighting wins by a wide margin. When gains broaden across many names, equal weighting takes over. Neither is permanently better.
Check three things: the combined weight of the top ten holdings, the fee difference, and the rebalancing schedule.
Top-ten weight in particular summarises the difference in one number. If it is far apart between two funds, you are comparing genuinely different products that happen to share an index name.
This article is general information, not investment advice. Investment decisions and responsibility are your own.