Relative Strength Index (RSI)

RSI (Relative Strength Index) is a momentum oscillator developed by J. Welles Wilder (1978) that measures the strength of recent price moves on a 0–100 scale; the default period is 14. Conventionally, readings above 70 are called overbought and below 30 oversold, but in a strong trend RSI can stay in the 70–90 zone for weeks — so the level alone is not a buy or sell signal.