The Relative Strength Index (RSI) is a momentum oscillator that measures the speed and magnitude of recent price changes to evaluate overbought or oversold conditions in an asset. Developed by J. Welles Wilder Jr., it oscillates between 0 and 100. A reading above 70 typically signals overbought conditions, while a reading below 30 suggests oversold conditions. The default lookback period is 14 candles, but traders adjust this for sensitivity. RSI is not a standalone buy/sell signal; it works best when combined with trend analysis, support/resistance, or other indicators. All trading involves risk, and no indicator guarantees future price moves.
RSI is built from the average gain and average loss over a chosen period. The formula is: RSI = 100 – (100 / (1 + RS)) where RS = Average Gain / Average Loss over the period.
For the initial calculation, the average gain and loss are simple averages of the 14 periods. After that, Wilder used a smoothing method to avoid sudden jumps: Average Gain = [(Previous Average Gain × 13) + Current Gain] / 14 Average Loss = [(Previous Average Loss × 13) + Current Loss] / 14 If there is no gain, the gain is zero; if no loss, the loss is zero. This smoothing makes RSI less erratic than a simple moving average of RS.
The classic thresholds are 70 and 30, but these are not rigid. In strong uptrends, RSI can stay above 70 for extended periods without a reversal. In downtrends, it can hover below 30. Some traders adjust levels to 80/20 for volatile assets like cryptocurrencies or to 60/40 in ranging markets. The key is context: overbought does not mean “sell immediately”; it indicates that upward momentum is extreme and a pullback or consolidation may be near. Oversold suggests the opposite.
1. Overbought and Oversold Crosses When RSI moves above 70 and then crosses back below, it can signal a potential short-term top. Conversely, crossing above 30 from below may hint at a bounce. However, these signals alone are prone to whipsaws in trending markets.
2. Divergence Divergence occurs when price and RSI move in opposite directions. Bullish divergence: price makes a lower low, but RSI makes a higher low. This suggests weakening downside momentum and a possible reversal upward. Bearish divergence: price makes a higher high, but RSI makes a lower high, warning of fading upside momentum. Divergence is more reliable when it appears at overbought/oversold extremes and is confirmed by price breaking a trendline.
3. Failure Swings Wilder described failure swings as strong reversal signals. A bearish failure swing: RSI rises above 70, pulls back, fails to exceed the prior peak on the next rally, and then breaks below the recent trough. A bullish failure swing is the mirror image below 30. These are less common but can provide high-probability setups.
4. Centerline Crossover The 50 level acts as a momentum barometer. RSI above 50 indicates average gains outweigh losses, favoring bullish momentum. A move from below 50 to above can confirm an uptrend, while a drop below 50 suggests bearish momentum. Many traders use 50 as a trend filter: only take long signals when RSI > 50, and short signals when RSI < 50.
Consider a stock with the following daily closing prices over 15 days (Day 0 to Day 14). We need 14 price changes to compute the initial RSI.
Day 1: $51 (gain 1) Day 2: $52 (gain 1) Day 3: $51 (loss 1) Day 4: $50 (loss 1) Day 5: $51 (gain 1) Day 6: $53 (gain 2) Day 7: $54 (gain 1) Day 8: $53 (loss 1) Day 9: $55 (gain 2) Day 10: $56 (gain 1) Day 11: $55 (loss 1) Day 12: $57 (gain 2) Day 13: $58 (gain 1) Day 14: $57 (loss 1)
Now, separate gains and losses for the 14 periods (Day 1 to Day 14): Gains: 1, 1, 0, 0, 1, 2, 1, 0, 2, 1, 0, 2, 1, 0 (losses are 0 for gain calculation) Losses: 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 1
Total Loss = 0+0+1+1+0+0+0+1+0+0+1+0+0+1 = 5
Average Loss = 5 / 14 ≈ 0.357
RS = 0.857 / 0.357 ≈ 2.40 RSI = 100 – (100 / (1 + 2.40)) = 100 – (100 / 3.40) ≈ 100 – 29.41 = 70.59
So the 14-day RSI is about 70.6, just into overbought territory. If the next day’s price rises to $58 (gain 1), the smoothed averages update: Previous Average Gain = 0.857, Current Gain = 1 New Average Gain = (0.857 × 13 + 1) / 14 = (11.141 + 1) / 14 = 12.141 / 14 ≈ 0.867 Previous Average Loss = 0.357, Current Loss = 0 (since it’s a gain) New Average Loss = (0.357 × 13 + 0) / 14 = 4.641 / 14 ≈ 0.332 RS = 0.867 / 0.332 ≈ 2.61 RSI = 100 – (100 / (1 + 2.61)) = 100 – (100 / 3.61) ≈ 100 – 27.70 = 72.30
This shows how RSI can climb further even when already overbought. The example illustrates why overbought alone is not a sell signal.
RSI can generate false signals in strong trending markets. During a powerful uptrend, RSI may stay overbought for weeks, and shorting based on that could lead to large losses. Similarly, in a crash, oversold readings can persist. Divergence can also fail: price may continue trending while RSI diverges for a long time before any reversal. Always use RSI with other tools like moving averages, volume, or trendlines.
Leverage, CFDs, and crypto trading amplify these risks. A false RSI signal on a leveraged position can wipe out capital quickly. Never rely on RSI alone for entry or exit. Implement strict risk management: define stop-loss levels, position size based on account risk (e.g., 1-2% per trade), and avoid overconfidence in any single indicator. Past performance does not guarantee future results.
- Identify the overall trend first (using a 200-period moving average or price structure). - Use RSI to spot potential turning points within that trend. - Look for divergence at overbought/oversold levels for higher-probability reversals. - Confirm with price action: wait for a candlestick reversal pattern or a break of a short-term trendline. - In ranging markets, overbought/oversold crosses can be more reliable; in trends, use RSI pullbacks to 50 or trendline breaks. - Adjust the period: shorter periods (e.g., 7) increase sensitivity; longer periods (e.g., 21) smooth signals. - Always set a stop-loss and take-profit based on market structure, not just RSI levels. - Backtest any RSI strategy on historical data before using real money.
Prepared with AlphaScala editorial tooling, examples, and risk-context checks against our education standards. General education only, not personalized financial advice.