Momentum is one of the most studied effects in finance. The basic idea is simple: assets that have performed well recently tend to keep performing well for a while, and weak ones tend to stay weak. A momentum trading strategy turns that tendency into rules.
What momentum trading is
Momentum strategies rank or filter assets by their recent performance and favor the strongest. Academic research going back to Jegadeesh and Titman’s 1993 study documented that stocks with strong returns over the previous several months tended to outperform over the following months.
Two main types of momentum
| Relative (cross-sectional) momentum | Absolute (time-series) momentum | |
|---|---|---|
| Question it asks | Which assets are strongest compared with the others? | Is this asset rising compared with its own past? |
| Typical rule | Buy the top-ranked stocks or ETFs by 6 or 12 month return | Hold an asset only while its trend is positive |
| Main benefit | Rotates into leaders | Can step aside in long declines |
Many traders combine them: rank assets by relative strength, but only hold those that also have positive absolute momentum.
A simple momentum strategy example
- Start with a defined universe, such as a list of sector ETFs or large-cap stocks.
- Once a month, rank them by total return over a lookback period, often 6 or 12 months.
- Buy the top few names in equal amounts.
- Optionally, move to cash or bonds for any pick whose own trend is negative.
- Repeat each month and replace names that fall out of the top group.
Risks to understand
- Momentum crashes. Momentum can reverse sharply, especially after a market bottom when beaten-down stocks rebound fastest.
- Turnover and costs. Frequent rebalancing adds trading costs and, in taxable accounts, taxes.
- Overfitting the lookback. Picking the exact lookback that worked best in the past is a form of curve fitting.
How to test a momentum strategy properly
Use long histories that include delisted symbols to avoid survivorship bias, include realistic trading costs, and check that results hold up across a range of lookback periods and universes rather than one perfect setting.
Choosing a lookback period
The lookback is the window used to measure momentum. Research has commonly looked at periods between about three and twelve months, and many practitioners skip the most recent month, because very short-term returns tend to partially reverse. There is no single correct choice. Shorter lookbacks react faster but trade more and generate more false signals. Longer lookbacks are steadier but slower to exit when leadership changes. Blending several lookbacks, such as an average of three, six and twelve month returns, is a common way to avoid depending on one exact setting.
Momentum and the universe you trade
Momentum behaves differently depending on what you apply it to. With individual stocks, it tends to produce more concentrated, volatile portfolios and higher turnover. With sector or asset class ETFs, the same idea becomes an ETF rotation strategy: a defined set of funds ranked on the same basis. Trading costs depend on the funds and how often the rules switch. Either way, the universe’s eligibility rules should be defined in advance. If you use index members, use the membership that existed on each historical date.
Ranking assets by recent performance is called relative strength ranking, and it is the engine behind most cross-sectional momentum strategies. Adding a simple trend rule, such as a moving average crossover or a check that price is above its long-term average, is a common way to add absolute momentum on top.
Position sizing and rebalancing
- Equal weight is the simplest approach and avoids betting too heavily on any one name.
- Volatility-adjusted weight holds smaller positions in more volatile assets, which can smooth the ride.
- Rebalancing frequency is usually monthly. Weekly rebalancing reacts faster but adds costs. Quarterly rebalancing lowers costs but can hold fading leaders too long.
- Buffer rules help reduce churn, for example only selling a holding when it drops well below the top group rather than the moment it slips one place.
When momentum struggles
Momentum tends to do well in markets with persistent trends and clear leadership. It tends to struggle in choppy, directionless markets, where rankings flip back and forth, and around sharp reversals, when the previous losers suddenly lead. Some of the worst momentum drawdowns in history came during rebounds after bear markets. Understanding this pattern helps set expectations and is one reason traders often combine momentum with other strategy styles rather than relying on it alone.
Leverage and momentum
Some traders apply momentum signals to leveraged ETFs to amplify gains. This also amplifies losses, and the daily reset of leveraged funds adds extra risk in volatile markets. Test any leveraged version separately, on the longest history available, before assuming it behaves like a larger version of the unleveraged strategy.
Questions to ask before trading momentum
- Can I hold through a sharp reversal without abandoning the rules?
- Are trading costs and taxes included in my test?
- Does the strategy still work with a slightly different lookback or universe?
- What will the rest of my portfolio be doing when momentum has a bad year?
Build a momentum trading strategy with Portfolio Boss
PB includes ranking rules such as Impulse Score, which ranks instruments by their percentage price gain over a selected period. Combine ranking with buy and sell filters to build a complete strategy, or let machine learning search for the rules and settings.
Instead of manually setting up one symbol after another, Strategy Mill builds and filters candidates across a symbol list. Your computer does the repetitive work; you review the survivors and decide how they fit together.
Portfolio Boss was built by trader Dan Murphy, who began trading in 1997. His focus goes beyond finding one attractive backtest: build a lineup of strategies with different strengths. Meta ML acts like an orchestra conductor, selecting which strategies trade each month. A momentum strategy can have a useful job in that team without carrying the entire portfolio.
Put your next idea to the test, free
Give your computer a symbol and let it build strategy ideas you can inspect and test. Portfolio Boss Evo is 100% free for life for the first 100,000 signups ($1,999 value). Download now. Advanced modules are paid.
Backtested and hypothetical results have limitations and do not guarantee future results.
