Why do equal-weighted indexes have higher rebalancing costs than cap-weighted indexes?
My CFA prep materials say equal-weight indexes require frequent rebalancing and incur higher costs. I thought equal weight was 'simpler' — just give every stock the same weight. Why does that create more trading and cost?
Equal-weighted indexes assign every constituent the same weight regardless of market cap. After any period, stock prices diverge and weights drift away from equality, requiring periodic rebalancing back to equal weight.
Why Rebalancing Is Necessary:
Suppose an equal-weight index has 5 stocks, each starting at 20% weight. After one month:
| Stock | Return | New Weight |
|---|---|---|
| Avalon Pharma (fictional) | +15% | 22.1% |
| Bristow Mining (fictional) | -8% | 17.7% |
| Calloway Retail (fictional) | +3% | 19.8% |
| Devereaux Systems (fictional) | +20% | 23.1% |
| Eastgate Financial (fictional) | -5% | 18.3% |
To restore equal 20% weights, you must sell winners (Avalon, Devereaux) and buy losers (Bristow, Eastgate). This is inherently contrarian.
Sources of Higher Cost:
- Turnover: Every rebalancing date requires trades in every constituent. A 500-stock equal-weight index needs 500 trades each quarter.
- Small-Cap Drag: Equal-weight gives the same weight to a $500M company as a $500B company. Small caps have wider bid-ask spreads and lower liquidity, increasing transaction costs.
- Frequency: Most equal-weight indexes rebalance quarterly. Cap-weighted indexes need no rebalancing for price changes — weights adjust automatically.
- Tax Inefficiency: Selling winners creates realized capital gains. Cap-weighted indexes rarely trigger taxable events from price-driven weight changes.
Cost Comparison:
| Factor | Cap-Weighted | Equal-Weighted |
|---|---|---|
| Rebalancing frequency | Rare (reconstitution only) | Quarterly |
| Annual turnover | ~5% | ~20-30% |
| Transaction costs | Very low | Moderate to high |
| Small-cap exposure | Minimal | Significant |
| Tax efficiency | High | Lower |
Exam Tip: The CFA exam contrasts cap-weighted and equal-weighted indexes. Remember: equal-weight has a small-cap tilt and contrarian bias (sells winners, buys losers), while cap-weight has a large-cap tilt and momentum bias.
Practice index weighting comparisons in our CFA Level I question bank.
Master Level I with our CFA Course
107 lessons · 200+ hours· Expert instruction
Related Questions
What exactly is the Capital Market Expectations (CME) framework and why does it matter for asset allocation?
How do business cycle phases affect asset class return expectations?
Can someone explain the Grinold–Kroner model step by step with numbers?
How do you forecast fixed-income returns using the building-blocks approach?
PPP vs Interest Rate Parity for forecasting exchange rates — when do I use which?
Join the Discussion
Ask questions and get expert answers.