The S&P 500 is usually described as a single thing, but the index can be built two very different ways. The standard version, tracked by funds like SPY and VOO, weights each of the 500 companies by market capitalization, meaning the largest firms dominate returns. The Invesco S&P 500 Equal Weight ETF, ticker RSP, takes the same 500 companies and assigns each one roughly 0.2% of the portfolio, regardless of whether it is a trillion-dollar technology firm or a mid-sized industrial company. That single structural choice produces a fund with a meaningfully different risk and return profile, even though the underlying holdings list is identical.
What Equal Weighting Actually Changes
In the cap-weighted S&P 500, the ten largest holdings have at various points since 2023 represented more than 35% of the total index, concentrated heavily in a handful of technology and communication services names. In RSP, those same ten companies make up roughly 2% of assets collectively, the same as any other group of ten constituents. The practical effect is that RSP's performance is driven far more by the median company in the index than by mega-cap outcomes. An investor holding RSP is making a statement about diversification across company size within a single index, rather than accepting whatever concentration the market happens to produce at a given moment.
The Rebalancing Mechanism
Equal weighting cannot stay equal on its own. If one stock rises 20% while the index average rises 10%, that stock's weight drifts upward and must be trimmed back to restore parity. RSP rebalances quarterly, in March, June, September, and December, selling down names that have outperformed and adding to names that have lagged, within the same fixed universe of 500 companies. This is a structural, rules-based form of mean reversion built into the fund itself, distinct from any judgment about valuation. It has historically produced higher turnover than cap-weighted funds — turnover for RSP has often run between 20% and 25% annually, compared with low single digits for a fund like VOO, which only needs to adjust for index additions, deletions, and share count changes.
Sector Tilts That Emerge
Because equal weighting removes the influence of company size, it also changes sector exposure indirectly. The cap-weighted S&P 500 has at times allocated over 30% to information technology alone, reflecting the scale of a small number of firms. RSP's sector weights are closer to a simple average of how many companies within each sector exist in the index, which has historically given it comparatively larger relative exposure to industrials, financials, materials, and mid-cap-style names, and comparatively smaller relative exposure to the largest technology platforms. This is not a sector bet in the traditional sense — RSP does not exclude or overweight any sector by design — but it is an emergent consequence of treating every company as equally important regardless of market value.
Historical Performance Patterns
Over different multi-year stretches, equal weighting has shown distinct behavior relative to cap weighting. During periods when market leadership broadened across many sectors and company sizes, such as parts of 2003 to 2007 or 2016 to 2018, RSP's structure has historically been associated with performance that kept pace with or modestly exceeded the cap-weighted index. During periods when a small number of very large companies drove most of the market's gains, such as much of 2020 through 2024, cap-weighted funds have historically outperformed because RSP's structure caps the influence of exactly those dominant names. Volatility has also differed at times, since equal weighting pulls in more mid-cap-style risk and reduces reliance on a small number of very liquid mega-caps. Neither pattern has held in every period, and past dispersion between the two approaches is not a forecast of future dispersion.
Costs And Turnover
RSP carries an expense ratio of 0.20%, higher than the 0.03% charged by some cap-weighted S&P 500 funds, reflecting the added complexity of quarterly rebalancing across 500 positions. The higher turnover also generates more taxable events inside the fund structure in a given year, which can matter for investors holding the ETF in a taxable account rather than a tax-advantaged one. These cost and structural differences are measurable and worth weighing independently of any view on which weighting method might behave better going forward.
Who This Structure Serves
Equal weighting is best understood as a different definition of what "the market" means, not a enhanced version of the standard index. An investor who believes that concentration risk in a handful of mega-cap companies is a meaningful exposure to manage may find the equal-weight structure addresses that concern directly, since no single company can ever represent more than roughly 0.2% of the fund at a rebalance date. An investor who views the largest companies' scale advantages as a durable reflection of their competitive position may prefer the cap-weighted approach, which lets winners compound their influence on the portfolio over time. Both are coherent, rules-based philosophies; they simply encode different assumptions about how company size relates to future business outcomes.
The rule to internalise
Equal weighting and cap weighting are not two versions of the same index with one being more correct — they are two different answers to the question of how much influence a company's size should have on a portfolio, and the dispersion between them tends to widen or narrow depending on how broadly or narrowly market leadership is distributed in a given period. Understanding which assumption a fund is built on matters more than knowing its historical return, because the assumption is what persists even when the numbers change.
Educational content only. Not investment advice.