RSI shows up on nearly every trading chart, and it's one of the most misunderstood numbers on it. Here's what it actually measures.
What it calculates
The Relative Strength Index (RSI) is a single number from 0 to 100 that summarizes the ratio of recent upward price moves to recent downward price moves, typically over the last 14 periods. Roughly: if the last 14 candles were mostly up moves, RSI sits high (closer to 100); if mostly down moves, RSI sits low (closer to 0); if it's a mix, RSI sits near 50.
That's it. It is not a prediction. It is a description of recent momentum, expressed as a single normalized number so it's comparable across different assets and price ranges.
What "overbought" and "oversold" actually mean
The conventional reading: RSI above 70 is "overbought," below 30 is "oversold." What that actually means is narrower than it sounds — it means recent price action has been unusually one-sided, not that a reversal is imminent. In a strong uptrend, RSI can sit above 70 for weeks while price keeps climbing; treating that as an automatic sell signal has cost a lot of traders a lot of upside.
The nuance that matters: overbought/oversold levels are much more informative within a regime than as a universal trigger. RSI < 35 in an established uptrend (a shallow pullback within a bigger move) is a very different signal from RSI < 35 in a confirmed downtrend (which can just mean "still falling"). The number is the same; what it implies isn't.
Level vs. cross
There's also a meaningful difference between two ways of using RSI:
- Level-based: act whenever RSI crosses below 30 or above 70. Simple, but can trigger repeatedly during a slow grind through the extreme zone.
- Cross-based: act only on a confirmed reversal — RSI was below 30 yesterday and crosses back above it today. A single, specific event rather than "still in the zone," which tends to produce fewer, more decisive signals.
Neither is universally correct; they're different tools that behave differently depending on how choppy the underlying market is.
Where RSI fails on its own
RSI, used alone, has no sense of the broader trend or regime — that's exactly what makes it dangerous as a standalone signal. It will happily flash "oversold" all the way down a real downtrend, because it only knows about the last 14 candles, not the structural context around them. That's why most durable uses of RSI pair it with a trend filter (only buy oversold readings when price is still above a longer moving average, for instance) rather than trading the RSI number in isolation.
RSI is a genuinely useful piece of evidence about recent momentum. It is not, by itself, a strategy — which is exactly why every RSI-based signal in Atradian's live strategy set (dip-buying, RSI-reversal, quiet-regime mean-reversion) pairs it with a trend or regime filter, and every one of those combinations has its own backtested, per-regime track record you can inspect in the Strategy Lab rather than trust on faith.