Relative Strength Index
Lexicon Core Definition
The Relative Strength Index is a momentum oscillator that quantifies recent price change velocity on a 0–100 scale to evaluate whether an asset is overbought, oversold, or trending with conviction.
Analysis Breakdown
Frequent Queries
What does the Relative Strength Index measure?
The Relative Strength Index measures momentum — specifically the ratio of recent price gains to recent price losses over a defined period, typically 14 candles. It normalizes this ratio into a value between 0 and 100. The higher the RSI, the stronger the recent upward price momentum relative to downward movement. The lower the RSI, the stronger the recent selling pressure. It does not measure price directly or predict direction — it quantifies the intensity of buying or selling momentum that has driven price in the recent window of time.
Who created the Relative Strength Index and why?
The Relative Strength Index was created by American mechanical engineer and technical analyst J. Welles Wilder Jr., introduced in his 1978 book 'New Concepts in Technical Trading Systems.' Wilder designed the RSI to solve a fundamental trading problem: measuring whether price was moving with genuine momentum or simply reacting to short-term noise. He wanted a single, normalized indicator that could identify when an asset had moved too far too fast, helping traders avoid chasing extended moves and instead find higher-probability entries and exits. It remains one of the most widely used indicators in existence today.
How is the Relative Strength Index different from other momentum indicators?
The Relative Strength Index is unique because it normalizes momentum into a fixed 0–100 scale, making it directly comparable across different assets and timeframes. Unlike MACD, which measures the distance between two moving averages and has no fixed boundaries, RSI always stays within its 0–100 range, making thresholds like overbought and oversold universally applicable. It is also distinct from pure price-based tools because it measures the internal strength of recent moves rather than absolute price levels, making it useful for identifying momentum divergence and exhaustion before price fully reflects the change.
Calibration Check
The Relative Strength Index compares one asset's strength against another asset.
Despite the word 'relative' in its name, the RSI does not compare one asset to another. It measures an asset's internal momentum relative to its own recent price history — specifically, comparing its own average gains against its own average losses. The 'relative' refers to the ratio of internal up-moves versus down-moves within the same asset's data. Confusing RSI with comparative strength analysis — such as comparing Bitcoin against Ethereum — reflects a misunderstanding of what the indicator actually calculates and displays.
A high Relative Strength Index reading means the asset is fundamentally overvalued.
RSI measures technical momentum, not fundamental value. A reading above 70 means price has risen quickly relative to recent history — it says nothing about whether the asset is priced correctly relative to its underlying value or utility. An asset can be fundamentally undervalued while showing an overbought RSI during a sharp short-term rally, or fundamentally overvalued while displaying an oversold RSI during a panic sell-off. Fundamental valuation requires separate analysis tools and frameworks that are entirely distinct from momentum-based indicators like RSI.
The Relative Strength Index works the same way in all market conditions.
RSI performs differently depending on whether the market is trending or ranging. In trending markets, RSI can remain in overbought or oversold territory for extended periods, making the standard 70 and 30 thresholds less reliable as reversal signals. In ranging markets, RSI oscillates more predictably between these thresholds. Experienced traders adjust their interpretation based on market context — using RSI to confirm trend continuation in trending markets and to identify potential reversals in range-bound conditions. Applying the same interpretation rigidly across all conditions leads to frequent misreads.