What Is the Relative Strength Index, and How Is It Misread?

What it measures

Over a lookback window, usually fourteen periods, the RSI compares the average size of upward closes with the average size of downward ones and expresses the result on a scale from zero to a hundred. High means recent gains dominated. Low means recent losses did.

That is all it says. It is a description of the recent past, compressed into one number, and every interpretation beyond that is something a reader adds. Keeping the measurement and the interpretation separate is what makes the rest of this page possible.

Scale

0 to 100

Default period

14

Measures

Recent gain vs loss

Predicts

Nothing by itself

Misreading one: treating a level as a signal

Above 70 is conventionally called overbought and below 30 oversold, and both terms smuggle in a conclusion. The reading states a condition, not an instruction. An asset can be above 70 for weeks, and during that period the condition is describing a strong uptrend rather than an imminent reversal.

Acting on the threshold alone means systematically selling strength and buying weakness, which is a coherent strategy in a range-bound market and an expensive one in a trending market. The indicator does not tell you which market you are in, which is precisely the information the threshold reading assumes.

Misreading two: using it in a trend

The RSI was built with mean reversion in mind, the idea that a stretched move snaps back. In a market that trends persistently, and crypto trends persistently, the indicator stays pinned at one end and produces a continuous stream of signals that are all wrong in the same direction.

The practical adjustment is to establish the regime first and only then read the indicator. In a range, threshold readings carry some information. In a trend, they mostly measure how strong the trend is, and divergence is the only reading with much left in it.

How the number is actually built

Take the closing changes over the lookback window and separate them into gains and losses. Average each. Divide the average gain by the average loss to get a ratio, then map that ratio onto a scale from zero to a hundred. A period with no losses reads 100; one with no gains reads zero.

Seeing the arithmetic makes the behaviour obvious. The reading is high when recent gains have been large relative to recent losses, which in a strong uptrend is simply true and stays true. Nothing in the formula contains a notion of "too far", which is the meaning people attach to a high reading.

The period setting changes what you are looking at

Nearly every chart defaults to fourteen periods, and nearly every discussion of the indicator treats that number as though it were part of the definition. It is a parameter. Shortening it makes the line reach the extremes far more often; lengthening it produces a smoother line that rarely does.

That matters because the thresholds people quote were popularised alongside the default. Keep the thresholds and change the period and the same reading now means something different, since the frequency of reaching it has moved. A short period touching an extreme is close to ordinary. A long one doing so is genuinely unusual.

The same applies to the timeframe underneath. An extreme reading on an hourly chart and the same reading on a weekly one are not comparable observations, and screenshots circulate without either setting being visible. Before treating any reading as information, check both numbers. If a source does not state them, the reading cannot be interpreted, which is a more common situation than it sounds.

Divergence, and why it is the defensible reading

Price makes a higher high while the indicator makes a lower one. That compares two measurements rather than reading a threshold, and it says something specific: the second move was made with less momentum behind it than the first.

It is also frequently early, sometimes by a long way, and early is indistinguishable from wrong while a position is open. Which is why divergence is better used as a reason to pay attention than as a reason to act, and why an indicator is at its most useful when it changes what you look at rather than what you do.