How to read RSI without getting trapped
RSI is the best-known indicator and the most misunderstood. "Above 70 it will drop" is wrong often enough to be expensive. Here is what it really measures.
What RSI measures, in plain words
RSI (Relative Strength Index) compares, over the last 14 candles, the average size of the up moves with the average size of the down moves. It returns a number from 0 to 100. That is all: it measures how strong the recent move was, not what comes next.
The maths fits in three lines. Take the average gain and the average loss, divide to get RS, then RSI = 100 − 100 / (1 + RS).
Example 1. Over 14 days the average gain is $1.20 and the average loss is $0.40. RS = 1.2 / 0.4 = 3. RSI = 100 − 100 / 4 = 75. Gains were three times stronger than losses.
Example 2. Average gain $0.50, average loss $1.50. RS = 0.33. RSI = 100 − 100 / 1.33 = 25. Here sellers dominate.
Trap 1: "70 = sell, 30 = buy"
The 70 and 30 levels only say "very strong move". In a solid uptrend RSI can stay between 60 and 80 for weeks: the price keeps climbing while RSI "shouts" overbought. Whoever sells at 70 exits early, sometimes very early.
The same exists on the way down: an RSI of 22 in a fall is not a floor, it is a fast fall. The number describes speed, not the end.
Trap 2: ignoring the bigger trend
A simple rule of thumb: in an uptrend RSI mostly swings between 40 and 80, and dips near 40-50 are its "breathing". In a downtrend it mostly swings between 20 and 60, and bounces to 55-60 often stall. Before looking at the number, look at the slope of the price on a wider chart.
An RSI of 35 does not mean the same in both contexts. In the first it is an unusual pullback; in the second it is normal.
Trap 3: reading one number instead of a shape
What matters most is often what RSI does relative to price. Example: price makes a new high at 105, but RSI peaks at 68 when it was 78 at the previous high. That is a divergence: the rise is running out of steam. It is not an order to sell, it is a warning that momentum is fading.
Another reading: the 50 line. An RSI that moves back above 50 and stays there says gains are regaining the upper hand; below 50, it is the losses.
A simple way to use it
- Look at the price trend first (up, down or flat).
- Then see where RSI sits in its usual range, not only versus 30 and 70.
- Look for a divergence or a cross of 50.
- Confirm with something else: a price level, volume, another timeframe.
RSI alone is never enough. It is there to ask a question ("is momentum changing?"), not to answer it.
What to remember
RSI measures recent speed and predicts nothing. The 30 and 70 levels are context alerts. The best approach is to read its shape, its range and its divergences, always keeping the trend in mind.
Results vary by asset and period: even well read, no indicator is right every time. Treat it as an aid to thinking.