What Is RSI? Relative Strength Index Calculation, Divergence & Trading Rules

Direct Answer: What Is RSI?

The Relative Strength Index (RSI) is a bounded momentum oscillator developed by J. Welles Wilder Jr. that measures the speed and change of price movements on a scale from 0 to 100. It evaluates average price gains against average losses over a standard 14-period window to identify potential overbought conditions, oversold extremes, and momentum divergences.

How RSI Is Calculated: Wilder's Smoothing Formula

Introduced in 1978 in New Concepts in Technical Trading Systems, the RSI standardizes raw price momentum into a normalized 0 to 100 oscillating band:

RSI = 100 - [ 100 / (1 + RS) ]

Where RS (Relative Strength) = Average Gain / Average Loss over N periods

Wilder's calculation utilizes a modified exponential smoothing process across two distinct phases:

Initial 14-Period Average: Calculate the simple average of all closing gains and the simple average of all closing losses over the first 14 trading periods.
Wilder's Smoothing (Subsequent Periods):
Current Average Gain = [ (Prior Average Gain × 13) + Current Gain ] / 14
Current Average Loss = [ (Prior Average Loss × 13) + Current Loss ] / 14

This smoothing technique dampens extreme outlier volatility while maintaining responsiveness to emerging momentum shifts. Combine RSI with volatility metrics like the Average True Range (ATR) to contextualize point moves.

Interpreting Overbought, Oversold & The 50 Centerline

Retail traders often misinterpret RSI boundary thresholds as mechanical buy and sell triggers. Understanding their true statistical meaning is essential:

Overbought Zone (Above 70)

Conventionally indicates that prices have risen rapidly relative to recent history. However, in strong structural bull trends, RSI can remain pinned above 70 for weeks while the stock doubles. It does not mean "sell immediately"; it signals that risk-reward for fresh long entries is deteriorating and trailing stops should be tightened.

Oversold Zone (Below 30)

Indicates severe downside velocity. In severe bear markets or corporate governance crises, stocks can drop another 30% while RSI is below 20. Oversold readings are constructive only when price aligns with key support and resistance levels and demonstrates a confirmed reversal.

The 50 Centerline Rule

The 50 line is the market equilibrium marker. When RSI crosses and sustains above 50, buyers control average price trajectory. In bullish trends, pullbacks frequently find support right at the 40–50 RSI zone before resuming their advance.

Mastering Divergence: Regular Reversals vs Hidden Continuations

Divergence occurs when price action and RSI oscillator trajectory decouple, signaling that underlying internal momentum disagrees with visible chart prices:

Divergence Type	Price Action	RSI Oscillator	Technical Signal
Regular Bullish	Makes Lower Lows	Forms Higher Lows	Downtrend momentum is exhausted; potential bullish reversal.
Regular Bearish	Makes Higher Highs	Forms Lower Highs	Uptrend momentum is failing; potential bearish reversal.
Hidden Bullish	Makes Higher Lows	Forms Lower Lows	Healthy momentum reset in an ongoing uptrend; strong continuation buy signal.
Hidden Bearish	Makes Lower Highs	Forms Higher Highs	Momentum reset in an ongoing downtrend; strong continuation short signal.

Execution Discipline: Combining RSI with Other Tools

Trading RSI divergences in isolation without trend confirmation generates frequent whipsaws during aggressive trend days. Experienced technical analysts enforce confluence rules:

Trend Context: Only trade regular bullish divergences when the macro 200-day moving average is flat or rising, or at major multi-month structural support zones.
Confirmation with Trend Oscillators: Wait for a bullish signal crossover on the MACD indicator strategy to confirm that moving average momentum has aligned with the RSI divergence.
Candlestick Confirmation: Ensure the divergence candle produces an identifiable price rejection formation, such as a hammer or bullish engulfing candle. Explore our master guide on technical chart analysis for systematic execution checklists.

Frequently Asked Questions: RSI Indicator

What does the Relative Strength Index (RSI) measure?

RSI is a bounded momentum oscillator that measures the velocity and magnitude of recent directional price movements on a scale from 0 to 100, evaluating whether an asset is experiencing overbought or oversold conditions.

What is the formula for calculating RSI?

RSI is calculated as: 100 - [100 / (1 + RS)], where RS (Relative Strength) is the average price gain divided by the average price loss over a designated lookback window (conventionally 14 periods) using Wilder's exponential smoothing.

Does an RSI above 70 mean you should immediately sell?

No. In strong structural bull markets, an asset can remain overbought above 70 for extended periods while prices continue climbing. Overbought RSI signals strong upward momentum; it indicates that traders should watch for divergence or confirmation rather than blindly shorting.

What is the difference between regular divergence and hidden divergence?

Regular divergence signals an imminent trend reversal (e.g., price makes higher highs while RSI makes lower highs). Hidden divergence signals trend continuation (e.g., price makes higher lows while RSI makes lower lows during a healthy pullback).

What is the significance of the 50 centerline in RSI?

The 50 level acts as a key momentum baseline. When RSI is sustained above 50, average gains exceed average losses, indicating a bullish momentum regime. When RSI is sustained below 50, bearish momentum dominates.