What is the S&P 100 Equal Weight Index?
The S&P 100 Equal Weight Index uses the same 100 blue-chip constituents as the S&P 100 but assigns an approximately equal weight to each company at each quarterly rebalance, rather than weighting by float-adjusted market capitalization. S&P Dow Jones Indices administers both the cap-weighted and equal-weight versions, making this pairing one of the clearest available examples of how weighting methodology changes index behavior without changing membership.
What Equal Weighting Means
Equal weighting is a straightforward approach to index construction: instead of letting each company's market capitalization determine how much it contributes to the index's value, every constituent starts each rebalance period with the same weight. In the S&P 100 Equal Weight Index, each of the 100 constituents begins each quarter with an approximately equal share of the total index value. This means the index assigns the same influence to a company with a smaller market capitalization as it does to a company many times larger.
The practical effect is that the index is significantly less dominated by the mega-cap names that lead the cap-weighted S&P 100. In the cap-weighted version, a company whose market capitalization is many times larger than its peers will have a weight many times larger as well. In the equal-weight version, that advantage disappears at each rebalance. The company still belongs to the index, but it starts each quarter on equal footing with every other constituent regardless of its absolute size.
Between quarterly rebalances, price movements allow individual weights to drift away from equal. A company whose stock rises rapidly will accumulate more weight as its price increases, while a company whose stock falls will see its weight decline. By the time the next rebalance arrives, weights may have drifted meaningfully from equal. The rebalance corrects this drift, selling the overweight names and buying the underweight ones to restore approximate equality. This systematic reset is what distinguishes equal-weight indexing from other approaches and what generates the characteristic turnover and size tilt that researchers associate with equal-weight strategies.
Comparison with the Cap-Weighted S&P 100
The S&P 100 and the S&P 100 Equal Weight Index share exactly the same member companies and the same administrator. The only structural difference is weighting methodology. This makes the two indexes ideal for isolating the effect of weighting on index behavior: any return difference between the two must come from the weighting approach rather than from differences in which companies are held.
When the largest companies in the S&P 100 by market capitalization outperform the smaller members of the 100-stock group, the cap-weighted version will generally produce better returns because it assigns more weight to those top performers. When the smaller members of the 100 outperform, the equal-weight version benefits because those companies have higher weights than their market caps would normally justify. This dynamic means the two indexes can diverge significantly during periods of uneven performance across the market-cap spectrum within the blue-chip universe.
Sector exposure also differs between the two. In the cap-weighted S&P 100, sectors with the largest companies by market cap receive higher aggregate weights. In the equal-weight version, each company contributes the same starting weight, so sectors with more constituents in the 100-stock universe benefit, regardless of how large those companies are relative to others. Investors should check current sector allocations directly from S&P Dow Jones Indices rather than inferring them from the cap-weighted version.
Rebalancing Mechanics
S&P Dow Jones Indices resets the S&P 100 Equal Weight Index to approximate equality on a quarterly schedule. The specific rebalance dates follow the same calendar that S&P Dow Jones Indices uses for the broader S&P equal-weight index family. At each rebalance, the index methodology determines new target weights and the index adjusts to reflect them. The rebalance also incorporates any membership changes that have occurred since the prior rebalance, such as additions or removals from the S&P 100 itself.
Between rebalances, the index runs passively in the sense that weights shift only with price movements and corporate actions. No manual weight adjustment occurs between scheduled rebalances unless a corporate event such as a merger, spin-off, or bankruptcy forces an out-of-cycle change. This means the index is not truly equal-weight at every moment during the quarter; it is equal-weight at rebalance and gradually diverges from equality as prices move. The equal-weight label describes the design intent and the state at each rebalance, not a continuous real-time property.
Sector and Size Effects of Equal Weighting
Equal weighting within the S&P 100 gives relatively more influence to the smaller companies within that 100-stock universe compared to what they would receive under cap-weighted methodology. If the S&P 100 includes companies from many different size ranges within the mega-cap and large-cap tier, equal weighting ensures that even the smallest members have meaningful starting influence on the index's performance. This creates what researchers often describe as a systematic size tilt: equal-weight indexes within a given universe tend to behave somewhat like a smaller-cap version of that universe's cap-weighted equivalent.
The tilt is relative, not absolute. Because the S&P 100 is already a universe of prominent blue-chip companies, even the smallest constituent is a large-cap stock by most measures. The size tilt in the S&P 100 Equal Weight is a tilt toward the smaller end of a mega-cap-and-large-cap universe, not a tilt into true small-cap territory. Investors who want exposure to genuine small-cap stocks would look to indexes with smaller-company universes rather than equal-weight versions of large-cap benchmarks.
Concentration Comparison
By construction, the equal-weight version of the S&P 100 is less concentrated than the cap-weighted version. In the cap-weighted S&P 100, the largest companies can have weights many times higher than the smallest. In the equal-weight version, the maximum and minimum weights at each rebalance are approximately equal. No single company can dominate the index at the moment of rebalancing, regardless of how large it has grown.
As weights drift between rebalances, some concentration will develop, but it is bounded by the next quarterly reset. The equal-weight design therefore imposes an upper limit on how concentrated the index can become over time, while the cap-weighted version allows concentration to grow indefinitely as the largest companies grow relative to their peers. This structural property makes equal-weight indexes appealing to investors who believe excessive concentration in market-cap-weighted benchmarks creates undue risk from the performance of a small number of very large companies.
Return Comparison Concepts
Whether the S&P 100 Equal Weight outperforms or underperforms the cap-weighted S&P 100 in any period depends on the relative performance of large-cap versus mid-size large-cap stocks within the blue-chip universe, not on any inherent superiority of either approach. Historical periods when the largest companies have driven market returns tend to favor cap-weighted indexes. Historical periods when returns have been more broadly distributed across company sizes within the large-cap tier tend to favor equal-weight approaches.
The higher turnover of equal-weight indexing is also relevant for fund tracking purposes. Because the quarterly rebalance requires systematic trading, an equal-weight fund tracking the S&P 100 Equal Weight Index will incur more trading costs than a cap-weighted fund with the same membership. These costs reduce net returns compared to the index, all else equal. Investors evaluating equal-weight products should consider expense ratios, trading costs, and any tax implications of the regular rebalancing in their total cost assessment.
Return Variants
Like the cap-weighted S&P 100, the equal-weight version is published in price return, total return, and net total return variants. The price return version excludes dividends; the total return version reinvests dividends at the ex-dividend date; the net total return version applies a specified withholding tax rate to dividends before reinvesting them. Researchers comparing the two versions of the index should use the same return variant for both to isolate the effect of weighting methodology rather than confounding it with dividend treatment differences.
Benchmark Use
The S&P 100 Equal Weight Index serves as a benchmark for strategies that seek exposure to major blue-chip companies without the concentration risk that comes with cap-weighted mega-cap indexing. Portfolio managers and researchers interested in studying equal-weight performance within a specific, well-defined blue-chip universe use this index to compare the effect of weighting methodology in isolation from membership differences. Because the membership is identical to the cap-weighted S&P 100, this pairing provides one of the cleanest natural experiments available in publicly available index research.
The index is also referenced by fund sponsors designing equal-weight products. ETFs and other fund structures that track the S&P 100 Equal Weight Index give investors access to the 100 blue-chip stocks in the S&P 100 universe without the mega-cap concentration of the standard cap-weighted version. Current product availability should be verified against fund providers' published listings, as availability changes over time.
Frequently asked questions
What is the S&P 100 Equal Weight Index?
The S&P 100 Equal Weight Index holds the same 100 blue-chip constituents as the S&P 100 but assigns an approximately equal weight to each company at each quarterly rebalance. S&P Dow Jones Indices administers both versions of the index.
How often does the S&P 100 Equal Weight Index rebalance?
S&P Dow Jones Indices resets the weights to approximate equality quarterly. Between rebalances, price movements cause individual weights to drift from equal. At each rebalance date, the weights are reset so no single company has a dominant position.
How does the S&P 100 Equal Weight differ from the S&P 500 Equal Weight?
Both are equal-weight versions of their parent cap-weighted indexes. The S&P 100 Equal Weight holds 100 blue-chip companies drawn from the S&P 500 with an options availability requirement, while the S&P 500 Equal Weight holds all S&P 500 constituents. The S&P 500 Equal Weight therefore provides broader coverage, while the S&P 100 Equal Weight focuses on major blue chips.
Why might an equal-weight index behave differently from a cap-weighted index?
Equal weighting gives smaller-company constituents the same starting influence as larger ones. In the cap-weighted S&P 100, the largest companies dominate because their higher market values translate directly into higher weights. In the equal-weight version, a company with a smaller market cap can have the same starting weight as the largest constituent, so the index is more sensitive to the performance of mid-size blue chips within the 100-stock universe.
Does the S&P 100 Equal Weight have more turnover than the S&P 100?
Equal-weight indexes generally have higher turnover than their cap-weighted counterparts because weights must be reset at each quarterly rebalance. In a cap-weighted index, weights adjust passively as prices move. In an equal-weight index, the reset requires selling stocks that drifted above equal weight and buying those that fell below, generating systematic turnover regardless of membership changes.