RSI — the Relative Strength Index — compresses the last couple of weeks of price moves into one number between 0 and 100. It is not measuring whether something is cheap or expensive. It is measuring speed: how fast and how one-directionally the price has been moving lately.
The two ends are the parts worth remembering. A reading over ~70 describes something that has risen fast — stretched, the way a runner who sprinted the last stretch may slow down. A reading under ~30 describes something that has fallen hard — sold off heavily, which is what "oversold" means. Both are descriptions of the recent past, not predictions: a fast rise can keep rising, and a hard fall can keep falling. The gauge tells you the move has been extreme, which is a reason to look closer — the trend lines and the market context say what it means.
Related: Volatility · “Is it just the market?” · The 200-day average · The five-questions worksheet
Last reviewed: November 8, 2026