Relative strength index (RSI) – 14D measures the speed and change of price movement over a 14 trading day period to determine whether a stock is in overbought or oversold range. RSI values range from 0 to 100. If the RSI is above 80, it is considered that a security is overbought zone or has run up too much and might fall soon. On the contrary if the RSI reading is below 20, it is considered that the security is oversold or has fallen too much and might see price reversal soon.
Relative strength is calculated using 14 trading days of price data. A simple average of daily price gains and daily price losses are compared with each other to calculate relative strength.