Momentum Investing
Momentum investing is an active investment strategy that systematically buys securities that have exhibited strong recent price performance and sells (or shorts) securities with weak recent performance, based on the empirical observation that past winners tend to continue outperforming and past losers tend to continue underperforming over a medium-term horizon of approximately 3–12 months.
Key takeaways
- The cross-sectional momentum factor was documented by Jegadeesh and Titman (1993), who showed that buying the top decile and shorting the bottom decile of stocks ranked by 12-1 month returns generates significant abnormal returns.
- Standard momentum signals use 12-month or 6-month return periods while skipping the most recent month to avoid reversal effects (short-term mean reversion in the 1-month window).
- Momentum investing is most effective during trending markets and suffers significantly during sharp reversals — momentum 'crashes' occurred in 2009 (post-GFC reversal) and March 2020 (post-COVID bottom).
- Dual momentum (combining absolute momentum — comparing asset returns to cash — with relative momentum) reduces crash risk by going to cash when all assets exhibit negative absolute momentum.
- The behavioral explanation for momentum attributes it to investor underreaction to information (slow diffusion of news) and subsequent herding that extrapolates trends beyond fundamentals.
Explanation
Momentum investing is one of the most robust and extensively documented phenomena in empirical asset pricing, having been shown to generate excess returns across equities, bonds, currencies, commodities, and alternative asset classes globally over long historical periods. Its discovery challenged the Efficient Market Hypothesis, which predicts that past returns should have no predictive power for future returns. Despite its long track record and academic recognition, momentum remains controversial because its source of returns — risk-based compensation or behavioral anomaly — continues to be debated.
The mechanics of equity momentum investing are straightforward in principle. At the end of each month, all securities in the investment universe are ranked by their returns over the past 3, 6, or 12 months (excluding the most recent month to avoid reversal contamination). The top decile (or quintile) — the 'winners' — is purchased; the bottom decile — the 'losers' — is sold short. The portfolio is rebalanced monthly or quarterly. The resulting long/short strategy has historically generated gross Sharpe ratios of 0.5–1.0 in the U.S. equity market, with similar performance internationally, representing a substantial and persistent return premium.
The primary risk of momentum investing is the momentum 'crash' — a sudden, sharp reversal that disproportionately punishes momentum portfolios. Crashes occur because momentum portfolios are typically long recent outperformers (often high-beta stocks in cyclical sectors that have been rising with the market) and short recent underperformers (often defensive, low-beta stocks). When market direction reverses sharply — as in the COVID-19 selloff and subsequent V-shaped recovery — the momentum portfolio's long book crashes while the short book rallies, creating simultaneous losses from both sides. Daniel and Moskowitz (2016) documented that momentum crash risk is predictable and concentrated in periods following extreme market downturns.
Modern momentum investing has evolved considerably from simple price-based ranking. Quality momentum strategies filter for stocks with both strong recent price performance and positive earnings revisions, avoiding 'bad' momentum from distressed or speculative companies. Factor momentum extends the concept beyond stocks to trade diversified factor portfolios based on the recent performance of value, size, profitability, and other systematic risk premia. Time-series momentum (also called trend following) applies momentum to the same asset across time — buying when the asset is trending above its historical average and selling or shorting when it is trending below — and is the foundation of the managed futures industry.
Formula
Momentum Signal = Return of Asset over [t−12, t−1] months (excluding month t)
Example
A quantitative equity fund runs a cross-sectional momentum strategy on the Russell 1000 universe. Each month, stocks are ranked by their 12-1 month returns. The top decile (average 12-1 return: +45%) is purchased in equal dollar weights; the bottom decile (average 12-1 return: −35%) is sold short in equal dollar weights. Over the trailing 20 years, this strategy generated an average annual return of approximately 8% on a dollar-neutral long/short basis (gross), with a standard deviation of 14% — a Sharpe ratio of approximately 0.57. However, the strategy lost 40% in just 3 months following the March 2009 market bottom, illustrating the severe crash risk embedded in momentum strategies.
Related terms
Basis Beta Cross Sectional Momentum Earnings Per Share Efficient Market Hypothesis Equity Gdr Global Depositary Receipt Managed Futures Margin Of Safety Premium Price To Sales Ratio Reversal