Momentum Factor
The momentum factor is a systematic tendency for securities that have outperformed over the recent past (typically 3-12 months) to continue outperforming over subsequent months, and for underperformers to continue underperforming.
The momentum factor is one of the most replicated findings in empirical asset pricing. First formally documented by Jegadeesh and Titman in their landmark 1993 paper, momentum strategies buy securities that have been recent relative winners and sell recent relative losers, holding positions for roughly 3 to 12 months before rebalancing. The strategy has generated positive returns across U.S. equities, international equities, bonds, commodities, and currencies over long historical periods.
Several behavioral explanations have been proposed for why momentum persists. Underreaction to information suggests that investors update their beliefs gradually rather than all at once, causing good news to be impounded into prices slowly, creating a drift that can be exploited. Herding behavior may cause investors to chase recent winners, generating further price appreciation. Disposition bias — the tendency of investors to sell winners too early and hold losers too long — also slows price adjustment.
Risk-based explanations have been less convincing. High-momentum stocks do not consistently carry higher traditional risk measures than low-momentum stocks, making it difficult to attribute the premium entirely to compensation for bearing systematic risk. This is part of why momentum has been called one of the most persistent and least explained anomalies in asset pricing.
Momentum's well-documented weakness is its exposure to sharp reversals, sometimes called momentum crashes. These typically occur during sudden market recoveries after steep declines, when recent losers (which momentum strategies have shorted) bounce back aggressively. The 2009 market recovery produced one of the worst momentum crashes on record. This crash risk means momentum strategies require careful position sizing and risk management.
Factor-based ETFs and smart beta strategies now give individual investors explicit access to momentum exposure. When blending momentum with other factors like value, some of the crash risk can be mitigated because value and momentum tend to be negatively correlated — momentum performs worst in recovery environments where value tends to do well.