The S&P 500 Equal Weight Index

This index holds exactly the same constituents as the S&P 500. The only difference is that each one gets an identical share rather than a share proportional to its market value, reset on a quarterly schedule.

That single change turns a company weighted at seven percent into one weighted at roughly two tenths of a percent — the same as the smallest constituent in the index.

What it is actually for

Its most valuable use is not as a portfolio. It is as a measurement of breadth.

When the headline S&P 500 rises sharply and the equal-weighted version does not, the gain came from the largest constituents. When they move together, participation was broad. No other single comparison tells you this as directly, which is why market commentary reaches for it constantly.

What equal weighting actually does

It creates a size tilt. Giving the 400th-largest company the same weight as the largest means the index is materially more exposed to the smaller end of the large-cap universe. Much of its performance difference is explained by that tilt rather than by the weighting scheme being cleverer.

It forces contrarian trading. Rebalancing back to equal weights means selling what has risen and buying what has fallen, every quarter, mechanically. Cap weighting does the opposite by construction: whatever appreciates automatically becomes a larger share.

It costs more to run. Quarterly rebalancing across 500 positions generates turnover that a cap-weighted index does not, and that turnover has a cost. Funds tracking equal-weight indexes generally carry higher expenses.

Facts worth knowing

• Identical constituents to the S&P 500The same 503 securities across 500 companies. Only the weights differ.
• Rebalanced quarterlyWeights drift with prices between rebalances and are reset on schedule.
• Every constituent is roughly 0.2%Against over 7% for the largest company in the cap-weighted version.
• It underperforms in concentrated marketsAnd tends to hold up better when leadership broadens — the mirror image of the headline index.
• Other equal-weight variants existIncluding sector-level equal-weight indexes, used for the same diagnostic purpose within an industry.

Common questions