Momentum Investing
The idea that trends tend to persist, and how momentum strategies are built.
⏱️ ~7 min read
Key Takeaways
- Momentum investing is based on the observation that securities that have performed well recently tend to continue performing well in the near term, and vice versa.
- Momentum has been documented across various markets and time periods in academic research, though explanations for why it exists remain debated.
- Momentum strategies can experience sharp, sudden losses ("momentum crashes") when trends reverse abruptly.
- Momentum is generally considered a shorter-to-medium-term strategy and tends to involve more frequent trading than buy-and-hold approaches.
What momentum investing is based on
Momentum investing is based on the empirical observation that securities (stocks, sectors, or other assets) that have performed relatively well over a recent period (commonly studied over periods like 3-12 months) have, on average, tended to continue performing relatively well over the subsequent period — and similarly, recent underperformers have tended to continue underperforming, at least over certain timeframes.
This is sometimes summarized as 'the trend is your friend' — rather than trying to identify undervalued or high-growth companies through fundamental analysis, momentum strategies focus primarily on price behavior itself as the signal.
Momentum has been documented in academic research across various markets, time periods, and asset classes, making it one of the more studied 'anomalies' relative to simple theories of market efficiency — though, as discussed below, why it exists remains a subject of debate.
How momentum strategies are typically built
A common approach involves ranking a universe of stocks based on their returns over a 'lookback period' (e.g., the past 6 or 12 months, sometimes excluding the most recent month to avoid short-term reversal effects), then favoring the top-performing stocks (and sometimes shorting the worst performers, in strategies that allow short-selling) for a subsequent 'holding period.'
This process is typically repeated on a rolling basis — periodically re-ranking and rebalancing the portfolio to maintain exposure to recent strong (or weak, for the short side) performers, which results in more frequent trading than buy-and-hold approaches.
Momentum can be applied at different levels — individual stock momentum (as described above), sector or industry momentum (favoring sectors that have recently outperformed), or even cross-asset momentum (applying similar logic across stocks, bonds, commodities, etc.).
Example
A simplified momentum approach might rank all stocks in an index by their total return over the trailing 12 months (excluding the most recent month), then hold the top 10% of performers for the next month, after which the portfolio is re-ranked and rebalanced. Stocks that have recently joined the top 10% would be added, while those that have fallen out would be sold — repeating this process continuously.
Why might momentum exist?
Several explanations have been proposed for why momentum has appeared in historical data, though none is universally agreed upon. Behavioral explanations suggest that investors may underreact to new information initially (causing prices to adjust gradually rather than instantly, creating a trend) and then potentially overreact later (extending the trend further than fundamentals justify).
Other explanations relate to how information spreads and gets incorporated into prices gradually across different types of investors, or to herding behavior (covered in our Stock Market Psychology category) where investors follow trends set by others.
It's worth noting that the existence of a historical pattern doesn't guarantee it will persist — some researchers have found that momentum effects have weakened or behaved differently in periods after they became widely known and studied, sometimes called the 'arbitrage' of documented anomalies once they become well-known.
- Behavioral underreaction/overreaction to news may contribute to trend persistence
- Herding behavior can amplify and extend price trends
- Momentum has been documented across many markets and periods historically
- Known anomalies can weaken once widely recognized and acted upon
Momentum crashes and risks
One of the most notable risks associated with momentum strategies is the 'momentum crash' — a sudden, sharp reversal where recent losers rebound sharply (and recent winners may fall), often around major market turning points, such as the transition out of a steep market decline.
These crashes can be particularly severe for momentum strategies because they tend to be concentrated and can happen quickly, sometimes erasing significant accumulated gains from the strategy in a short period — a markedly different risk profile than the gradual, broad declines associated with simply holding a diversified market portfolio.
Because of the trading frequency involved, momentum strategies can also incur higher transaction costs and, in taxable accounts, potentially less favorable tax treatment (due to shorter holding periods triggering short-term capital gains) compared to longer-term buy-and-hold approaches — factors that can meaningfully affect net returns for individual investors attempting to replicate institutional momentum strategies.
Frequently Asked Questions
Is momentum investing the same as day trading?+
No — momentum investing, as studied academically and applied by some institutional strategies, typically involves holding periods of weeks to months based on medium-term trends, which is quite different from day trading's intraday focus (covered in our Trading Education category), though both involve more frequent activity than buy-and-hold.
Can individual investors implement momentum strategies?+
Some funds and ETFs are designed to follow momentum-based approaches, offering individual investors exposure without needing to implement the ranking and rebalancing process themselves. Attempting to replicate academic momentum strategies directly involves complexity, costs, and risks (like momentum crashes) that are worth understanding first.
Does momentum contradict the idea that 'past performance doesn't guarantee future results'?+
Not exactly — momentum research describes a historical statistical tendency over specific timeframes, not a guarantee for any individual security. The standard disclosure about past performance refers to the general principle that historical returns of any specific investment don't ensure similar future returns, which remains true even for assets currently exhibiting positive momentum.