What it means
The idea is simple: strong performance tends to attract more buyers, while weak performance tends to attract more sellers. Over short to medium periods this can produce trends, even though no one can predict exactly when a trend will end.
Researchers have documented the effect across many markets and time periods, and it is one of the best-known factors in investing alongside value and size. Explanations include investors reacting slowly to news, herd behaviour and the way analysts revise their forecasts gradually.
Measurement is straightforward. The most common approach compares today's price with the price some months ago, often skipping the most recent month to avoid short-term reversals, and then ranks assets from strongest to weakest.
Traders also use momentum indicators such as the rate of change and moving averages. These tools smooth out noise and show whether buying or selling pressure is strengthening or fading.
The risks are real. Momentum can reverse abruptly, especially after sharp market turning points, and strategies built on it often trade frequently, so costs and taxes can reduce the net return.
Momentum also has a business meaning. Managers talk about sales momentum or commercial momentum when growth is building on itself, and lenders and investors look for evidence that the pattern is supported by real customers and cash flow.
In practice
Real-world examples.
Example
A portfolio manager ranks 500 shares by their 12-month return, excluding the latest month, and buys the top 10%. She reviews the list every month and replaces any holdings that have fallen out of the top group. The process is rules-based, which keeps emotion out of the decisions.
Example
A retail trader notices that a technology share has risen for eight weeks and closed above its 50-day average. He buys a small position and sets a stop-loss order in case the trend reverses. He accepts that some trades will lose money and relies on cutting those losses quickly.
Example
A software company's chief executive tells the board that the business has strong commercial momentum, with new contracts up 40% year on year. The board asks for pipeline data to confirm that the growth is likely to continue. They want to see signed contracts and renewal rates, not only enthusiasm.
Formula
Calculation
Price momentum = (Current price / Price N months ago) - 1
A share was priced at $80 six months ago and is now $100. Momentum over six months is ($100 / $80) - 1 = 1.25 - 1 = 0.25, or 25%. A second share rose from $50 to $55 over the same period, giving ($55 / $50) - 1 = 0.10, or 10%. Ranked by this measure the first share has the stronger momentum, but a careful investor would also check volatility, because a 25% gain earned with wild swings is less reliable than a steady 10%.Case study
Seen in the real world.
Northgate Capital is an illustrative, fictional investment firm that ran a small momentum strategy on a $5,000,000 portfolio for a group of private clients. It bought the 20 best-performing shares from a list of 200 and rebalanced monthly.
For 18 months the approach worked well and the portfolio beat its benchmark by 4 percentage points a year. Then the market turned sharply, and many of the former leaders fell fast while the previous laggards bounced back, causing a loss of 12% in a single quarter.
After the loss the fictional team reviewed the results and added a volatility limit, a cap on any one sector and a rule to reduce exposure when markets fell sharply. They also began to report net returns after trading costs, which showed that frequent rebalancing had absorbed almost a full percentage point of the gain.
Watch out
Common mistakes.
- Assuming past winners will always keep winning, when momentum can reverse suddenly.
- Ignoring trading costs and taxes, which can eat a large part of the benefit in a high-turnover strategy that trades every month.
- Confusing momentum with fundamentals, when a rising price may have nothing to do with improved earnings or cash flow.
Questions
People also ask.
Is momentum the same as trend following?
They are related, but momentum usually compares assets against each other, while trend following looks at one asset's direction over time. Both rely on persistence, and both can suffer when markets reverse.
How long does momentum last?
Studies typically find it works over periods of a few months to a year, then fades, and very recent moves can partly reverse. No one can say exactly when a trend will end, which is why risk limits matter.
Can momentum be applied to a business?
Yes, managers talk about sales or growth momentum, which means improvement that builds on itself. It still needs to be backed by real demand and cash.
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