RSI (Relative Strength Index)
The Relative Strength Index is the most-used oscillator in trading — and the most misused. Used correctly it measures momentum and warns of exhaustion; used naively it produces endless false signals. Here's how to use it like a pro.
What RSI measures
RSI is a momentum oscillator that moves between 0 and 100, measuring the speed and magnitude of recent price changes. The default setting is 14 periods. Readings above 70 are traditionally 'overbought' and below 30 'oversold' — but those labels are where most traders go wrong.
In a strong uptrend, RSI can stay above 70 for a long time. Selling simply because RSI is 'overbought' is a classic way to fight a trend and lose. Overbought/oversold are context, not triggers.
Divergence: RSI's best signal
The highest-value RSI signal is divergence — when price and RSI disagree. Bullish divergence: price makes a lower low but RSI makes a higher low, hinting that downside momentum is fading. Bearish divergence is the mirror. Divergence at a key level, with a confirming candle, is a genuine edge.
How to actually use RSI
- Use divergence at key support/resistance, not raw overbought/oversold
- In trends, treat the 40–50 zone as support (uptrend) or resistance (downtrend)
- Always confirm with price action — RSI is secondary, price is primary
- Don't stack RSI with three other momentum tools; that's redundancy, not confluence
| RSI behaviour | Interpretation |
|---|---|
| Bullish divergence at support | Momentum shift up — watch for reversal |
| RSI holds 40–50 in uptrend | Trend intact — pullback buy zone |
| >70 in strong uptrend | Strength, not a sell signal |
| Loses 50 after long uptrend | Momentum cooling — caution |
Key takeaways
- RSI = momentum oscillator, 0–100, default 14
- Overbought/oversold = context, NOT triggers
- Best signal = divergence at a key level
- Trends: 40–50 acts as dynamic support/resistance
- Confirm with price — RSI is secondary
Test your knowledge
1. What is RSI's most reliable signal?
2. In a strong uptrend, RSI above 70 usually means…
Frequently asked questions
The default 14 is fine for most traders. Lower periods (e.g. 7) are more sensitive and noisier; higher periods smooth signals. Don't over-optimise — focus on divergence and context.
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