The short answer: a market-cap-weighted ETF represents the market by giving larger companies larger weights. An equal-weight ETF holds the same index companies at roughly equal company weights after each rebalance. Equal weighting reduces dependence on the largest names, but it adds smaller-company, value, sector and rebalancing exposures. It changes the risk rather than removing it.
The choice is therefore not “concentrated versus diversified.” Both versions can hold the same S&P 500 companies. The decision is whether you want the market’s current weights or a rules-based strategy that repeatedly sells relative winners and buys relative laggards to restore equal weights.
How the two weighting rules differ
| Feature | Market-cap weighted | Equal weighted |
|---|---|---|
| Starting weight | Proportional to free-float market value | Approximately equal for each company at rebalance |
| Between rebalances | Weights move naturally with relative market values | Weights drift away from equal as prices move |
| Trading need | Mainly index changes, share updates and corporate actions | Quarterly reset plus index changes and corporate actions |
| Largest-company influence | Can become substantial when market leadership narrows | Reset to roughly the same company weight as every other constituent |
| Relative exposure | Represents the investable market segment | More exposure to the smaller companies and different sectors within that segment |
| Primary trade-off | Concentration in market leaders | Higher turnover, implementation cost and factor deviation |
What equal weighting changes in the S&P 500
S&P Dow Jones Indices reports that the ordinary S&P 500 is float-adjusted market-cap weighted. Its 31 August 2026 snapshot showed the largest constituent at 8.1% and the ten largest constituents together at 37.8%.
The S&P 500 Equal Weight Index uses the same companies but resets each company to approximately 0.2% at its quarterly rebalance. Immediately after a simplified equal-weight reset, ten companies account for about 2% rather than 37.8%. Their weights then drift until the next reset.
| Measure | S&P 500 market-cap weight | S&P 500 equal weight at rebalance |
|---|---|---|
| Largest company | 8.1% on 31 August 2026 | About 0.2% |
| Ten largest companies | 37.8% on 31 August 2026 | About 2.0% in total |
| Each company’s performance contribution | Proportional to its current index weight | Starts approximately equal after rebalance |
The equal-weight figures are a method illustration, not a live holdings snapshot. Multiple listed share classes and market movement can make the precise security-level weights differ from a simple 500-company division.
Lower concentration creates other tilts
Equal weighting underweights today’s largest companies and overweights the smaller companies inside the same selected universe. In the S&P 500, those are still companies chosen for a large-cap index, but the resulting portfolio behaves more like a smaller-company strategy than the market-cap version.
Sector weights also change. If the largest technology companies dominate the market-cap index, equal weighting reduces their influence and raises the relative weights of sectors containing more smaller constituents. That can help when market leadership broadens and hurt when mega-cap leaders keep outperforming.
Vanguard’s regression of monthly returns for the Russell 3000 Equal Weighted Index from January 2000 to March 2026 found a positive value tilt and a negative momentum tilt relative to the market-cap-weighted Russell 3000. That evidence is not a measurement of the S&P 500 Equal Weight Index, although a similar reweighting mechanism can create related size, value and momentum exposures. Those factor exposures can be rewarded for long periods or disappoint for long periods. Equal weighting is a systematic active choice even though the rules are transparent.
Why rebalancing raises turnover
Market-cap weighting is self-adjusting. If one company rises 20% while the rest stand still, its index weight rises without the fund needing to buy it solely to restore a target. Equal weighting does the opposite at each reset: it sells companies that have grown above the equal target and buys those that have fallen below it.
This creates a disciplined contrarian mechanism, but it requires trading. Vanguard reports that, for the ten years to November 2024, the S&P 500 Equal Weight Index had on average more than five times the two-way turnover of the market-weight S&P 500, using S&P Dow Jones Indices data.
Turnover is not an annual fee printed beside the TER. Its effect can appear through trading costs, market impact, tax inside or outside the fund, and tracking. Compare the exact ETF’s ongoing charge and matched-period tracking difference rather than assuming the index return reaches the investor unchanged.
A simple rebalancing example
Assume a €10,000 portfolio contains 500 companies. A perfectly equal 0.2% allocation starts each company at €20. If one company doubles while every other company is unchanged, that position becomes €40 and the portfolio becomes €10,020. Its weight rises to about 0.40%.
At the next equal-weight reset, the target is close to €20.04 per company before considering real index mechanics. The strategy sells much of the doubled position and reallocates across the others. A cap-weight portfolio lets the doubled company keep its higher weight.
This mechanical difference explains both the appeal and the risk. Equal weighting realises a “trim winners, add to laggards” rule. It can underperform when the winners continue to lead.
Do not compare unmatched funds
A clean comparison uses funds tied to the same parent universe. Comparing an equal-weight S&P 500 ETF with a total-market or global market-cap ETF mixes weighting, company selection and geography.
Check:
- the exact index and return version;
- UCITS status, domicile and share class;
- ongoing charge and historical tracking difference;
- rebalance frequency and turnover;
- spread, assets, exchange and broker commission;
- whether currency hedging or ESG screens add another difference.
The TER versus tracking difference guide explains how to separate the stated fund charge from historical implementation.
Decision framework
- Market-cap weighting fits an investor seeking the market’s current composition, lower turnover and minimal deviation from the standard benchmark.
- Equal weighting fits an investor deliberately seeking lower mega-cap concentration and accepting smaller-company, value, sector and rebalancing exposure.
- Neither should be chosen from recent returns alone. The relative winner changes with market leadership and factor performance.
- Cost matters. Compare fund fees, tracking, spread and tax consequences alongside the concentration objective.
Equal weighting is not a repaired version of the market. It is a different portfolio with explicit relative bets. Market-cap weighting is not automatically unsafe because its leaders are large. The better choice is the rule whose exposures and maintenance costs match the role of the holding.
Frequently asked questions
Does an equal-weight ETF hold different companies?
Not necessarily. The S&P 500 Equal Weight Index uses the same companies as the S&P 500, then applies a different weighting rule. Other equal-weight indexes can use different selection rules, so verify the exact methodology.
Is equal weighting less risky?
It reduces dependence on the largest constituents but increases other risks, including exposure to smaller companies, different sectors, value and rebalancing. Volatility can be higher.
Does equal weighting always buy low and sell high?
It trims relative winners and adds to relative laggards at scheduled rebalances. That rule can help when returns mean-revert and hurt when strong companies continue outperforming.
Which approach has performed better?
The answer depends on the period. Historical leadership reflects company-size, sector, value and momentum cycles as well as costs. A selected past period does not establish the next winner.
Sources and limitations
S&P Dow Jones Indices’ S&P 500 page provides the float-adjusted market-cap method and the 31 August 2026 concentration snapshot. Its S&P 500 Equal Weight page documents the same-company universe, approximate 0.2% company weights and quarterly rebalancing. The S&P U.S. Indices Methodology describes both construction rules.
Vanguard’s July 2026 analysis discusses turnover, sector, size, value and momentum differences. Vanguard is an issuer and expresses a preference for market-cap weighting; the underlying methodology facts are separated here from that conclusion.
Concentration figures are dated snapshots and will change. The €10,000 example is deterministic, ignores fees and tax, and does not model a real ETF. This guide does not predict which weighting method will outperform.