RSI Calculator — Relative Strength Index

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How this is calculated

The Relative Strength Index (RSI), developed by J. Welles Wilder in 1978, is a momentum oscillator that measures the speed and magnitude of recent price changes to evaluate overbought or oversold conditions. It runs on a scale from 0 to 100.

The calculation starts with the average gain and average loss over a chosen period (Wilder used 14 periods). In Wilder's original method, these are smoothed exponential moving averages: the first value is a simple average over the period, and subsequent values use the smoothed formula (new average = (prior average × (n − 1) + current value) / n). This calculator accepts the already-smoothed average gain and average loss directly, which is the value you would read from a charting platform after the indicator has warmed up. The Relative Strength ratio RS = Avg Gain / Avg Loss is then converted to RSI with the formula RSI = 100 − 100 / (1 + RS), which compresses it into the 0–100 range.

RSI above 70 is traditionally interpreted as overbought (the asset may have rallied too far, too fast) and below 30 as oversold (the asset may have sold off too far, too fast). These are not automatic sell or buy signals — overbought conditions can persist for extended periods during strong trends, and divergence between RSI direction and price direction is often considered a more robust signal. RSI is best used in combination with other indicators and price action context.