RSI: How to Use the Relative Strength Index
The RSI measures whether a market is overbought or oversold by comparing recent gains to recent losses. Learn how to read RSI levels, spot divergence, and avoid the most common RSI trap that costs beginners money.
The Relative Strength Index (RSI), developed by J. Welles Wilder in 1978, is one of the most popular momentum indicators in trading. It measures the speed and magnitude of recent price changes to tell you whether a market is moving too far, too fast in either direction.
How RSI Works
RSI compares average gains to average losses over a lookback period (default 14 candles) and outputs a number between 0 and 100. A reading near 100 means recent gains have vastly outpaced losses. A reading near 0 means the opposite.
Reading the RSI Levels
| RSI Level | Interpretation | Implication |
|---|---|---|
| Above 70 | Overbought | Momentum is high — potential pullback |
| 50–70 | Bullish momentum | Uptrend intact |
| 50 | Neutral midpoint | Watch for directional break |
| 30–50 | Bearish momentum | Downtrend intact |
| Below 30 | Oversold | Selling is extreme — potential bounce |
The Most Common RSI Mistake
Beginners see RSI hit 70 and immediately sell, expecting a reversal. In a strong trend, RSI can stay above 70 for weeks. Selling every overbought reading in a bull market is a losing strategy.
Do Not Fight the Trend with RSI
In a strong uptrend, RSI touches 70–80 repeatedly and each touch is continuation, not reversal. Use RSI to confirm trends, not to pick tops and bottoms against them.
RSI Divergence: The Real Signal
Divergence occurs when price and RSI disagree. It is the most powerful RSI signal.
| Type | Price | RSI | Signal |
|---|---|---|---|
| Bearish divergence | Higher high | Lower high | Weakening momentum — possible reversal down |
| Bullish divergence | Lower low | Higher low | Weakening selling — possible reversal up |
Bearish Divergence Example
Nifty rallies to 24,500 (RSI 72), pulls back, then rallies to 24,800 (new high) but RSI only reaches 65. Price made a new high; RSI did not. This divergence warned of exhaustion before the reversal.
RSI as Trend Filter: The 50 Line
RSI consistently above 50 suggests a bullish trend. Consistently below 50 suggests a bearish trend. This simple rule keeps you on the right side of the market.
How to Actually Use RSI
In an uptrend, buy when RSI pulls back to 40–50. In a downtrend, sell when RSI bounces to 50–60. This uses RSI with the trend, not against it.
Key Takeaways
- RSI ranges from 0 to 100. Above 70 is overbought; below 30 is oversold.
- In strong trends, RSI can stay overbought or oversold for extended periods.
- RSI divergence — price makes a new high but RSI does not — is an early warning of trend exhaustion.
- The 14-period RSI is the standard default setting.
- RSI is most reliable when used with trend context, not in isolation.