Why Momentum Investing Works — Academic Evidence and Behavioral Finance

Most investors hear "momentum investing" and picture day traders glued to screens, chasing green candles. That image is wrong, and it is costing people money.

Momentum is one of the most rigorously proven factors in all of academic finance. It sits alongside value and size in the pantheon of market anomalies that have survived decades of scrutiny, replication, and real-world testing. Yet most retail investors either dismiss it as speculation or have never seriously considered it.

Today I want to unpack why momentum works, what the academic research actually says, and why a rules-based momentum approach might be the single best antidote to the behavioral mistakes that cost average investors 2-4% per year in lost returns.

The Academic Foundation of Momentum

The systematic study of momentum begins with Jegadeesh and Titman's landmark 1993 paper. Their finding was straightforward but powerful: stocks that performed well over the past 3-12 months continued to outperform over the subsequent 3-12 months. Stocks that performed poorly continued to underperform.

This was not a one-time statistical fluke.

Hundreds of follow-up studies confirmed the same pattern. Across U.S. equities, European markets, Asian markets, emerging markets. Across bonds, commodities, and currencies. Momentum is one of the very few factors that transcends time, geography, and asset class.

Here is the part that should make you pay attention. Eugene Fama — the father of the efficient market hypothesis, the man who spent his career arguing that markets instantly reflect all available information — called momentum "the premier market anomaly." Coming from Fama, that is an extraordinary admission. It means that even within the framework of efficient markets, momentum should not exist. But it does.

So why does it persist?

Three Structural Reasons Momentum Works

1. Institutional Money Piles Into Winners

Large institutional investors — pension funds, mutual funds, hedge funds — have a structural incentive to concentrate capital in stocks that are already rising. The reason is simple: holding winners makes quarterly reports look good.

This is called window dressing. At the end of each quarter, institutions clean up their portfolios by increasing positions in outperformers and trimming losers. This creates additional buying pressure on winning stocks, reinforcing the very momentum that attracted them in the first place.

It is not just individual fund managers. Index rebalancing, ETF inflows, and algorithmic trading systems all push in the same direction. Winners attract more capital. More capital drives further gains. The cycle feeds itself.

2. Trends Persist Longer Than People Expect

Most market participants suffer from mean reversion bias — the intuitive belief that "what goes up must come down." But the data tells a different story. Uptrends last significantly longer than most people anticipate.

Why? Because markets do not incorporate new information instantaneously. Information is reflected in prices gradually. When a company reports strong earnings, the stock jumps that day. But the reaction does not stop there. Follow-up analyses get published. Analyst price targets get revised upward. Institutional buying programs kick in. This process plays out over weeks and months.

A single positive catalyst is not a one-day event. It triggers a cascade of positive reactions that extend the trend far beyond what most investors expect.

3. Human Psychology Drives Continuation

The most fundamental engine of momentum is human greed and fear.

When prices rise, investors grow more confident that they will continue rising. FOMO kicks in. Latecomers pile in, creating additional upward pressure. When prices fall, fear spreads. Panic selling creates additional downward pressure.

This is a pattern as old as markets themselves. It operated in the Dutch tulip mania. It operated in the dot-com bubble. It operated in the COVID crash of 2020.

Behavioral economists connect this to the disposition effect: people sell winners too early and hold losers too long. This systematic irrationality across millions of market participants is what creates momentum at the aggregate level.

Behavioral Mistakes and the Momentum Solution

Here is where it gets personal.

The average retail investor underperforms the market by 2-4% annually. DALBAR's annual report confirms this year after year. When the S&P 500 returns 10%, the average individual investor earns 6-8%.

The gap is not caused by bad stock picks. It is caused by bad timing. More specifically, emotional timing.

Markets crash, and investors sell in panic. Markets surge, and investors buy in euphoria. The result is a repeated pattern of buying high and selling low. Every investor believes they are making rational decisions. In reality, they are making the worst decisions at the worst possible moments.

A rules-based momentum system addresses this problem structurally. An ETF like SPMO rebalances automatically every six months. No human emotion is involved. The rules are predetermined: mechanically rotate into winning stocks, rotate out of losing stocks.

The absence of emotion is the greatest advantage.

When markets crash, the system does not panic sell. When markets soar, the system does not chase at the top. It follows the rules. Period.

I believe this is the most underappreciated benefit of momentum investing. The excess returns from the momentum factor matter, yes. But eliminating behavioral mistakes — the 2-4% annual drag that most investors impose on themselves — may matter even more.

Long-Term Performance and Current Market Conditions

Year over year and decade over decade, momentum has beaten the market. This is supported by extensive academic research and actual fund performance data.

But what about right now?

As of 2026, SPMO is down roughly 4% year-to-date. This is expected behavior. In choppy, directionless markets, momentum strategies struggle. Momentum shines when there are clear trends. It weakens when volatility is high and direction is unclear.

Understanding this is critical. Momentum is not a strategy that wins every month or every quarter. Short-term underperformance happens. Month-to-month volatility can be higher than the broad market.

But when you extend the time horizon to one year, three years, ten years — the picture changes dramatically. Momentum has consistently generated excess returns over long periods, and the structural reasons behind it — institutional behavior, gradual information incorporation, human psychology — are not going away.

Risks and Counterarguments: Momentum Is Not Perfect

Let me be fair about the risks.

Severe losses during trend reversals. The biggest vulnerability of momentum strategies appears when markets reverse sharply. After the 2009 financial crisis, the momentum factor experienced extreme drawdowns. Long-short momentum strategies — which short declining stocks and buy rising ones — get hit on both sides when reversals occur.

Transaction costs and tax drag. Rebalancing every six months means transaction costs. In an ETF wrapper, investors do not pay these directly, but they are reflected in the expense ratio. Momentum strategies are inherently less tax-efficient than buy-and-hold approaches.

Crowding risk. As momentum strategies become more popular, there is a theoretical risk that too much capital chasing the same stocks could erode the excess returns. The data has not shown clear evidence of this yet, but it remains a legitimate concern.

Underperformance in sideways markets. As noted, choppy markets without clear trends are momentum's weakest environment. The current market may be exactly this type of environment.

My Assessment

I believe momentum investing is a sound strategy for most individual investors.

The reasoning is straightforward. The behavioral correction alone — eliminating the 2-4% annual performance drag from emotional decision-making — is worth more than the momentum premium itself. Over a 20- or 30-year investment horizon, compounding that difference creates enormous wealth disparity.

That said, I would not recommend allocating 100% of a portfolio to momentum. The risk of underperformance in sideways markets and sharp reversals argues for using momentum as a component of a diversified portfolio, not the entirety of one.

Momentum does not ask "why is this stock going up?" It only asks "is it going up?" That simplicity is its strength. A system free of emotion, backed by decades of academic validation, designed to exploit the very irrationality that costs investors billions every year. That is why momentum has survived for as long as markets have existed, and why it will likely continue to work for as long as human beings are the ones making investment decisions.