What Is the RSI Indicator?
The Relative Strength Index (RSI) is a momentum oscillator developed by J. Welles Wilder in 1978. It measures the speed and magnitude of recent price changes to evaluate whether an asset is overbought or oversold. RSI is displayed as a line that oscillates between 0 and 100, and it remains one of the most widely used indicators in both stock and forex trading.
How RSI Is Calculated
RSI is calculated using the average gains and average losses over a specified period — most commonly 14 periods (bars). The formula is:
RSI = 100 − [100 / (1 + RS)]
Where RS (Relative Strength) = Average Gain / Average Loss over the chosen period.
You don't need to calculate this manually — every trading platform computes RSI automatically. But understanding the formula helps you appreciate what the indicator is actually measuring: the ratio of bullish momentum to bearish momentum.
Reading the RSI: Overbought and Oversold Levels
The traditional interpretation uses two key threshold levels:
| RSI Level | Interpretation | Common Signal |
|---|---|---|
| Above 70 | Overbought | Potential sell/short signal |
| 30–70 | Neutral zone | No clear signal |
| Below 30 | Oversold | Potential buy/long signal |
However, be cautious: in a strong uptrend, RSI can remain above 70 for extended periods. An overbought reading alone is not a sell signal — it simply means momentum is elevated. Always confirm with price action or other indicators.
RSI Divergence: A Powerful Reversal Signal
RSI divergence occurs when the price and the RSI indicator move in opposite directions. This is one of the most reliable signals the RSI produces.
Bullish Divergence
Price makes a lower low, but RSI makes a higher low. This indicates that downside momentum is weakening even as price continues to fall — a potential reversal to the upside.
Bearish Divergence
Price makes a higher high, but RSI makes a lower high. This indicates that upside momentum is fading even as price continues to rise — a potential reversal to the downside.
RSI Trading Strategies
Strategy 1: The 50-Level Crossover
The RSI midpoint of 50 acts as a trend filter. When RSI crosses above 50, it signals that bulls are in control and the trend is shifting upward. When it crosses below 50, bears are in control. Many trend-following traders use this as a simple trend confirmation tool.
Strategy 2: Overbought/Oversold in a Range
In a sideways (ranging) market, buying when RSI drops below 30 and selling when it rises above 70 can be an effective mean-reversion strategy. Combine with support and resistance levels for higher-probability setups.
Strategy 3: Divergence + Confirmation Candle
Wait for RSI divergence to form, then look for a confirming candlestick pattern (such as an engulfing candle or a pin bar) before entering a trade. This two-factor confirmation greatly increases the reliability of the signal.
RSI Settings: Adjusting the Period
- 14 periods (default): Balanced sensitivity — suitable for most trading styles.
- 7 periods (faster): More signals, but more false signals. Better for short-term trading.
- 21 periods (slower): Fewer, cleaner signals. Better for swing or position trading.
RSI vs. Stochastics: Key Differences
Both RSI and Stochastics are momentum oscillators, but RSI measures the velocity of price change while Stochastics compares closing price to a price range over time. RSI tends to be smoother and less prone to whipsaws, making it a preferred choice for traders who want fewer but more reliable signals.
Final Thoughts
The RSI is a versatile, powerful tool when used correctly. The key is to avoid using it in isolation — combine RSI signals with trend direction, price action confirmation, and proper risk management for the best results.