Introduction
Quantitative trading relies on mathematical models to identify market opportunities. Among hundreds of existing strategies, two families have dominated for decades: momentum (trend following) and mean reversion.
These two approaches are based on diametrically opposed assumptions about price behavior. Understanding their mechanisms, strengths, and weaknesses is essential for any systematic trader.
Info
This article presents the fundamental concepts of these two strategies with illustrative data. Past performance does not guarantee future results.
Key Figures
Momentum Sharpe Ratio
0.85
Mean Rev. Sharpe Ratio
1.12
Momentum Max Drawdown
-28%
Mean Rev. Win Rate
63%
Momentum: Riding the Trend
Momentum is based on an empirical observation: assets that have performed well recently tend to continue performing well, and vice versa. This market anomaly, documented by Jegadeesh & Titman (1993), remains one of the most robust in finance.
How Does It Work?
- Calculate past returns over a rolling window (e.g., 12 months)
- Rank assets from best to worst
- Buy the top decile, sell the bottom decile
- Rebalance monthly or quarterly
Historical Performance of a 12-Month Momentum Strategy
Growth of €10,000 — Momentum vs Buy & Hold
Conseil
Momentum works best over intermediate horizons (3 to 12 months). Below one month, mean reversion effects dominate. Beyond 12 months, the effect fades.
Momentum Strengths and Weaknesses
Momentum captures major market trends and can generate superior long-term returns. However, it suffers from sudden crashes (momentum crashes) during market reversals, as in 2009 or March 2020.
Mean Reversion: Betting on a Return to Normal
Mean reversion is based on the opposite assumption: extreme prices tend to revert to their historical average. When an asset has risen "too much," it falls back. When it has fallen "too much," it bounces back.
Classic Indicators
- RSI (Relative Strength Index): buy below 30, sell above 70
- Bollinger Bands: buy at the lower band, sell at the upper band
- Z-Score: measures deviation from the mean in standard deviations
Trading Signals — RSI on a Volatile Stock
RSI and Signal Zones
Formule
RSI = 100 − (100 / (1 + RS)) where RS = Average gains / Average losses over N periods (usually N = 14)
Monthly Returns of a Mean Reversion Strategy
Monthly Returns — RSI Mean Reversion Strategy
Head-to-Head Comparison
Momentum vs Mean Reversion
Momentum
- Captures major bullish and bearish trends
- Works across stocks, futures, FX, crypto
- Typical Sharpe Ratio: 0.6 – 1.0
- Significant drawdowns during market reversals
- Optimal horizon: 3 to 12 months
- Low win rate (~45%) but large individual gains
Mean Reversion
- Exploits temporary excesses and market overreaction
- Works best on stocks and pairs (pairs trading)
- Typical Sharpe Ratio: 0.8 – 1.3
- Risk of unlimited loss if price doesn't revert
- Optimal horizon: 1 day to 4 weeks
- High win rate (~60-65%) but small individual gains
Les deux stratégies sont complémentaires : le momentum performe en marché directionnel, le mean reversion en marché range. Les combiner réduit la volatilité globale du portefeuille.
Combining Both Approaches
The best quantitative funds don't choose between momentum and mean reversion: they combine both. The negative correlation between these strategies offers a natural diversification benefit.
Combined Performance
Cumulative Returns — Combined Strategy vs Individual
Conseil
By combining 50% momentum and 50% mean reversion, the max drawdown drops from -28% to -15% while the annualized return remains comparable. That's the power of strategy diversification.
Conclusion
Momentum and mean reversion are the two pillars of quantitative trading. Rather than picking a side, experienced practitioners combine them to build more robust portfolios.
The key is understanding when each strategy works and properly sizing positions to survive unfavorable periods.
Attention
Backtesting alone is not enough. Transaction costs, slippage, and liquidity constraints can significantly reduce performance in real conditions. Always test in paper trading before deploying capital.
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