Relative Strength

Index (RSI)

Relative Strength Index (RSI)

One of the more popular computer-generated technical indicators is the Relative Strength Index (RSI) oscillator. (An oscillator, defined in market terms, is a technical study that attempts to measure market price momentum—such as a market being overbought or oversold.)

The Relative Strength Index (RSI ) is a J. Welles Wilder, Jr. trading tool. The main purpose of the study is to measure the market's strength or weakness. A high RSI, above 70, suggests an overbought or weakening bull market. Conversely, a low RSI, below 30, implies an oversold market or dying bear market. While you can use the RSI as an overbought and oversold indicator, it works best when a failure swing occurs between the RSI and market prices. For example, the market makes new highs after a bull market setback, but the RSI fails to exceed its previous highs.

Another use of the RSI is divergence. Market prices continue to move higher/lower while the RSI fails to move higher/lower during the same time period. Divergence may occur in a few trading intervals, but true divergence usually requires a lengthy time frame, perhaps as much as 20 to 60 trading intervals.

Selling when the RSI is above 70 or buying when the RSI is below 30 can be an expensive trading system. A move to those levels is a signal that market conditions are ripe for a market top or bottom. But it does not, in itself, indicate a top or a bottom. A failure swing or divergence accompanies the best trading signals.

The RSI exhibits chart formations as well. Common bar chart formations readily appear on the RSI study. They are trendlines, head and shoulders, and double tops and bottoms. In addition, the study can highlight support and resistance zones.


As you just read above, some traders use these oscillators to generate buy and sell signals in markets-—and even as an overall trading system. However, we treat the RSI as just one trading tool in our trading toolbox. We use it in certain situations, but only as a “secondary” tool. We tend to use most computer-generated technical indicators as secondary tools when we are analyzing a market or considering a trade. My “primary” trading tools include chart patterns, fundamental analysis and trend lines.

Oscillators tend not to work well in markets that are in a strong trend. They can show a market at either an overbought or oversold reading, while the market continues to trend strongly. Another example of oscillators not working well is when a market trades into the upper boundary of a congestion area on the chart and then breaks out on the upside of the congestion area. At that point, it’s likely that an oscillator such as the RSI would show the market as being overbought and possibly generate a sell signal—when in fact, the market is just beginning to show its real upside power.

We do look at oscillators when a market has been in a decent trend for a period of time, but not an overly strong trend. We can pretty much tell by looking at a bar chart if a market is “extended” (overbought or oversold), but will employ the RSI to confirm our thinking. We also like to look at the oscillators when a market has been in a longer-term downtrend. If the readings are extreme-—say a reading of 10 or below on the RSI-—that is a good signal the market is well oversold and could be due for at least an upside correction. However, we still would not use an oscillator, under this circumstance, to enter a long-side trade in straight futures, as that would be trying to bottom-pick.

Oscillators are not perfect and are certainly not the “Holy Grail” that some traders continually seek. However, the RSI is a useful tool to employ under certain market conditions.