Equal-weight and capitalisation-weighted indices

How constituent influence is assigned

Market capitalisation is share price multiplied by shares outstanding. Many index methods adjust it for shares available to public investors and may apply other limits. A high price per share alone does not establish a high index weight: the number of shares and the methodology matter.

Equal weights do not remain equal between rebalances because prices move differently. Restoring equal weights generally trims relative winners and adds to relative laggards. This changes exposure to company size and sectors and can require trading. It is a weighting rule, not proof that the smaller constituents are better investments.

Worked example: −3% versus +3.33%

Imagine three companies with starting capitalisation weights of 60%, 30% and 10%. During one period their total returns are −10%, +5% and +15%. Ignore fees, corporate actions and any rebalancing within the period. The capitalisation-weighted result is 0.60 × (−10%) + 0.30 × 5% + 0.10 × 15% = −3%.

An index beginning with one-third in each company returns (−10% + 5% + 15%) / 3 ≈ +3.33%. The 6.33-percentage-point difference comes from weights, not from owning different names. If the largest company instead leads the gains, the capitalisation-weighted version may outperform. Neither method wins by definition.

Equal weights still carry unequal risks

Equal capital weights do not mean equal risk contributions. Smaller constituents may be less liquid, and sector weights can differ substantially. Rebalancing frequency, eligibility and corporate-action rules matter. A fund tracking either index incurs expenses and implementation costs that are absent from a theoretical index calculation.

Check the index version before comparing

Compare available closed daily, weekly or monthly bars over the same dates, then verify which index version and return convention each series represents. Obtain constituent weights and methodology from the index provider. Student Wyckoff Pro supports closed-bar analysis; index construction, fund expenses and holdings information must be checked separately.

Primary sources

Sources explain the mechanics and limitations; the editorial examples use invented numbers rather than market quotations.

• S&P U.S. Indices Methodology

Sources checked: 2026-10-23