The Relative Strength Index (RSI) is a technical index used to analyze financial markets. It compares the magnitude of recent losses and gains so as to assess the overbought or oversold conditions of a particular asset. This assessment allows the investor to determine when it is wise to purchase or sell a particular stock.
The formula used in making the assessment is:
RSI = 100-100/(1+RS)
(where RS is equal to the average of x days’ up closes/Average of x days’ down closes)
RSI is charted on a scale of 0-100 points. Once the RSI of an asset exceeds 70 it is considered to be overbought. The odds are that it is overpriced at that point and the investor should expect a correction in price. If the RSI drops below 30 the stock is considered to be oversold and may become undervalued.
Fluctuations within the RSI can be dramatic at times, so it is not always an accurate measure of what a stock may be doing. One of the things that RSI may indicate is an upcoming turn in the market, especially if there is a wide divergence between the strength index and the price action. A bear divergence occurs when a stocks’ price reaches a new high but the RSI doesn’t achieve a matching high. A bull divergence is the opposite with new lows reached.
The disadvantage of using just RSI to track a stock is that large surges or declines can create false buy or sell conditions. Best employed to complement other assessment techniques, the Relative Strength Index (RSI) may provide warning if a stock is not trading at a price commensurate with its worth.