Technical Analysis·Technical Indicators
RSI: Relative Strength Index
Measuring Market Momentum
The RSI (Relative Strength Index), developed by J. Welles Wilder in 1978, is the most widely used momentum oscillator in trading. It measures the speed and magnitude of recent price changes, oscillating between 0 and 100. While simple on the surface, RSI has several powerful applications beyond the basic overbought/oversold reading that most beginners learn.
Wilder introduced RSI in his book 'New Concepts in Technical Trading Systems,' and it quickly became the standard momentum indicator across all financial markets. The formula compares the average of up closes to the average of down closes over a period (default 14), producing a single number that reveals whether buying or selling pressure is dominant.
Definition
Relative Strength Index (RSI)
A momentum oscillator that measures the ratio of average gains to average losses over a set period (default: 14 periods). It oscillates between 0 and 100. Above 70 is traditionally considered overbought; below 30 is considered oversold. The 50 level acts as the neutral line — above is bullish momentum, below is bearish. The formula is: RSI = 100 - (100 / (1 + RS)), where RS = Average Gain / Average Loss.
Definition
RSI Period
The number of periods used in the RSI calculation. The default is 14, which Wilder chose as a balance between sensitivity and smoothness. Shorter periods (7, 9) make RSI more sensitive and produce more signals (and more false signals). Longer periods (21, 25) make it smoother and more reliable but slower to react.
Reading RSI Correctly
The overbought/oversold trap
Most traders misuse RSI. In a strong uptrend, RSI can stay above 70 for weeks. Blindly shorting because RSI is 'overbought' in a bull market will get you destroyed. Overbought and oversold readings are only meaningful at potential reversal zones — not in the middle of strong trends. RSI above 70 in an uptrend means 'strong' not 'sell.'
| RSI Level | Interpretation | Best Use |
|---|---|---|
| 80-100 | Extreme overbought — very strong bullish momentum | Only fade at major resistance with reversal confirmation |
| 70-80 | Overbought — strong bullish momentum | Look for reversal signals at tops, but don't short blindly in uptrends |
| 50-70 | Bullish momentum zone | Hold longs, look for buy dips in trending markets |
| 50 | Neutral line — the momentum equilibrium point | Crossover above 50 = bullish momentum; below 50 = bearish |
| 30-50 | Bearish momentum zone | Hold shorts, look for sell rallies in downtrends |
| 20-30 | Oversold — strong bearish momentum | Look for reversal at bottoms, don't buy blindly in downtrends |
| 0-20 | Extreme oversold — very strong bearish momentum | Only buy at major support with reversal confirmation |
An RSI of 70 indicates strong bullish momentum. The traditional overbought level is 70, but in strong trends, adjusting the threshold to 80 reduces false sell signals. Many professional traders use 80/20 instead of 70/30 for overbought/oversold thresholds in trending markets.
RSI Divergence — The Hidden Signal
RSI divergence is one of the most powerful signals in technical analysis. It occurs when price makes a new high or low but RSI fails to confirm it. This divergence reveals weakening momentum — the trend is running out of steam even though price is still moving in the trend direction. Divergence is a leading signal, meaning it often predicts a reversal before it happens.
Definition
Bullish RSI Divergence
Price makes a new lower low, but RSI makes a higher low. Signals that despite price falling further, selling momentum is weakening. Often precedes a reversal to the upside. The divergence reveals that less selling energy is required to push price to new lows — sellers are exhausting themselves.
Definition
Bearish RSI Divergence
Price makes a new higher high, but RSI makes a lower high. Signals that despite price moving higher, buying momentum is fading. Often precedes a reversal to the downside. Buyers are having to work harder for diminishing returns — a classic sign of exhaustion.
Definition
Hidden Divergence
A continuation signal (opposite of regular divergence). Hidden bullish divergence: price makes a higher low while RSI makes a lower low — the trend is resetting momentum before continuing upward. Hidden bearish divergence: price makes a lower high while RSI makes a higher high — the downtrend is preparing to resume.
| Divergence Type | Price Action | RSI Action | Signal | Use Case |
|---|---|---|---|---|
| Regular Bullish | Lower low | Higher low | Reversal upward | Buying opportunity at support |
| Regular Bearish | Higher high | Lower high | Reversal downward | Selling opportunity at resistance |
| Hidden Bullish | Higher low | Lower low | Continuation upward | Trend-following long entry |
| Hidden Bearish | Lower high | Higher high | Continuation downward | Trend-following short entry |
Real-world divergence example: USD/JPY bearish divergence
In November 2022, USD/JPY made a new high at 151.94 but RSI peaked at only 67, compared to 79 on the previous high at 148.80 in October. This textbook bearish divergence — higher price, lower RSI — warned that buying momentum was exhausted. Within a week, USD/JPY collapsed from 151.94 to 133.60, a decline of over 1,800 pips. The RSI divergence was visible several days before the crash began.
Divergence in practice
EUR/USD makes a new low at 1.0600, but RSI only reaches 28 vs 22 on the previous low. This bullish divergence (lower price, higher RSI) suggests selling pressure is drying up. Combine this with a bullish candlestick reversal at support for a high-conviction long setup.
Bearish RSI divergence: price makes new high at 1.1050 but RSI peaks at 65 vs 72 on prior high — momentum is fading. Bearish reversal followed.
Divergence on higher timeframes
RSI divergence on the daily and weekly charts is far more significant than on lower timeframes. A weekly RSI divergence can signal a major trend change weeks or months in advance. When you spot divergence on the daily chart, zoom into the H4 for your entry timing — you get the reliability of the daily signal with the precision of the H4 entry.
Entry
1.2180
Stop
1.2130
Target
1.2330
Bullish RSI divergence on GBP/USD daily chart. Price made a lower low at 1.2160, but RSI bottomed at 28 vs 22 on the prior low. A bullish hammer formed at the 1.2180 support zone on the H4 chart. Entry above the hammer at 1.2180, stop below the support at 1.2130, target at previous resistance at 1.2330. R:R approximately 1:3.0.
Knowledge check
USD/JPY makes a new high at 152.00, but RSI registers only 65 compared to 74 on the previous high at 151.00. What does this signal?
Knowledge check
In a strong uptrend, RSI has been consistently between 50 and 80 for three weeks. RSI currently reads 72. Should you sell?