Relative Strength Index (RSI) Deep Dive
Learn how the Relative Strength Index measures stock price momentum, identifies overbought or oversold conditions, and signals potential trend reversals.
🎯 Key Learning Objectives
- ✓RSI is a momentum oscillator that ranges from 0 to 100.
- ✓Traditional thresholds are 70 for overbought and 30 for oversold, but adjustment based on market conditions is common.
- ✓Divergence between price action and RSI trendlines is one of the strongest reversal signals.
- ✓RSI does not indicate when a trend will end; an asset can remain overbought or oversold for extended periods during strong trends.
What is the Relative Strength Index (RSI)?
Developed by J. Welles Wilder Jr. in 1978, the Relative Strength Index (RSI) is one of the most widely used momentum oscillators in technical analysis. It measures the speed and velocity of directional price movements, plotting the results on a scale from 0 to 100.
At its core, the RSI compares the magnitude of a stock's recent gains to the magnitude of its recent losses. This provides traders with insight into whether a stock is experiencing buying pressure (becoming overbought) or selling pressure (becoming oversold).
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The Mathematical Formula
To understand what RSI represents, it helps to examine its mathematical construction:
Where RS (Relative Strength) is calculated as:
Typically, Wilder's original smoothing period of 14 days is utilized as the default lookback window. For any given day, gains and losses are isolated: - If today's closing price is higher than yesterday's, the gain is the difference, and the loss is zero. - If today's closing price is lower than yesterday's, the loss is the difference, and the gain is zero.
The initial averages are calculated as simple arithmetic means over the 14 days, while subsequent periods use Wilder's smoothing technique: $$\\text{Average Gain} = \\frac{\\text{Previous Average Gain} \\times 13 + \\text{Current Gain}}{14}$$
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Interpreting RSI Values
Overbought (70+) and Oversold (30-) The standard interpretation of the RSI dictates that values above **70** indicate an asset has become overbought (suggesting it may be overvalued or due for a corrective pullback). Conversely, values below **30** indicate the asset is oversold (suggesting it may be undervalued or primed for a relief rally).
The Midline (50) Center The **50 midline** serves as a helpful trend indicator. When the RSI crosses above 50, it suggests that average gains are outpacing average losses, signaling bullish momentum. When it falls below 50, it suggests bearish momentum. Many trend-following systems use the 50 midline to confirm entries.
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Advanced Signals: Divergence and Reversals
Among professional technical analysts, the most powerful signals generated by the RSI are divergences. A divergence occurs when the price of the stock moves in the opposite direction of the RSI oscillator.
1. Bullish Divergence A bullish divergence occurs when the stock price makes a **lower low**, but the RSI makes a **higher low**. This suggests that despite the downward price pressure, the downward momentum is slowing down, indicating a potential reversal to the upside.
2. Bearish Divergence A bearish divergence occurs when the stock price makes a **higher high**, but the RSI makes a **lower high**. This indicates that although the price is rising, the buying momentum is weakening, suggesting a potential trend exhaustion and downward reversal.
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Best Practices for Screening Stocks using RSI
When using the MiroMint AI Stock Screener, combining RSI with other indicators increases strategy win rates. - RSI Pullback Strategy: Filter for stocks with high long-term AI scores (e.g., score > 80) whose daily RSI has pulled back to between 30 and 40. This identifies high-quality stocks experiencing temporary short-term selling. - RSI Breakdown Filter: Scan for stocks with low AI scores (score < 40) whose RSI is breaking down below the 50 midline. This indicates a potential transition into a long-term bearish trend.