The Aroon Indicator: What the 0-100 Reading Actually Counts

Five widely read explanations of this indicator were read in full while preparing this page. Three of them state that the default period is 25. Two state that it is 14. None of the five cites anything for the number it gives, and none mentions that the other figure exists. A reader who opens one page and sets the indicator accordingly has adopted a charting package’s house setting under the impression that it belongs to the indicator.

The Default Period Is Not 25, and It Is Not 14 Either

The lookback period is the only setting the indicator has, and it is the one thing the available explanations do not agree on. The same disagreement runs through the documentation for the Vortex Indicator, which suggests the fault belongs to how indicator pages are written rather than to either tool. Three of the five put it at 25. Two put it at 14, and one of those two also recommends 25 to 30 for longer holding periods a few paragraphs later.

Not one of the five attributes its figure to anything. Each states it in the voice of a fact about the indicator rather than a fact about the software, which is what it is. A charting package ships a value in the settings box, that value gets repeated by whoever writes about the indicator next, and the repetition becomes a convention nobody has checked.

The distinction is worth holding because the period changes what the reading means, not merely how sensitive it is. A 14-bar window and a 25-bar window ask different questions about the same chart: one asks whether the extreme happened in roughly the last fortnight of bars, the other in roughly the last month of them.

So the setting is a choice a reader makes, and the honest description of any figure printed as a default is that it is the value that particular tool happened to ship. Where leading and lagging indicators differ in what they claim to see, this one differs in how far back it agrees to look, and that is entirely under the reader’s control.

What the Number Actually Counts

Every one of the five presents the 0 to 100 scale as a gauge of trend strength, sitting in the same paragraph as other momentum tools. That framing is where the confusion starts, because the number is not built from price at all.

The calculation looks at the chosen window and finds which bar inside it carries the highest high. It then counts how many bars have passed since that bar. That count is subtracted from the period, divided by the period, and multiplied by 100. Aroon Down does the same thing with the lowest low.

The consequence is that the reading is a statement about timing and nothing else. If the highest high of the window is on the current bar, the reading is 100, and it is 100 whether that high exceeded the previous one by a fraction of a pip or by a very large distance. A page can go on producing marginal new highs and hold a reading of 100 the entire time.

That makes it a different kind of instrument from anything that measures how far price travelled. The extremes it watches are the same ones behind the highest high and lowest low over a lookback, but where a channel plots the price level of those extremes, this reading throws the level away and keeps only their age.

Reading the Number Back Into Bars

Because the number is a rescaled count, it converts back exactly. Every bar of delay costs 100 divided by the period, so the scale advances in fixed steps rather than continuously.

At a 25-bar period each bar is worth 4.0 points, and the only readings that can appear are 100, 96, 92, 88 and so on down to 0. At a 14-bar period each bar is worth about 7.14 points and the attainable set is a different one. A reading of 72 on a 25-bar setting is not a vague signal of a weakening trend; it says the highest high of the window is seven bars old.

The 50 row is the one worth pausing on. A reading of exactly 50 requires the extreme to sit precisely half a window back, so it exists only when the period is an even number. On a 25-bar setting the value 50 never prints at all, and any rule written around crossing it is describing something the indicator cannot do at that setting.

Aroon Up and Aroon Down Are Two Independent Counts

The two lines are produced by two separate measurements. One tracks the age of the highest high in the window, the other the age of the lowest low, and nothing in the arithmetic ties them together.

They are not complements. Aroon Down is not 100 minus Aroon Up, and a reader who assumes it is will misread every chart where both lines are elevated. Both can be high at the same time, which happens when the window contains a recent high and a recent low, and both can be low at the same time, which happens when the window contains neither.

Those two states describe genuinely different conditions. Two high readings mean the range is being extended in both directions inside a short span of bars. Two low readings mean the current window has produced no new extreme in either direction for a long stretch, and price is working somewhere inside the boundaries set earlier.

The second of those is the more common and the more often misread, because a pair of low readings can look like an absence of information when it is an observation in its own right. Two-line indicators differ in how independent the lines are: on the Relative Vigor Index the second line is derived from the first rather than measured separately.

The Oscillator Is the Difference Between Them

The oscillator that carries the same name is not a separate indicator with its own measurement. It is Aroon Up minus Aroon Down, plotted as one line.

Because both inputs run from 0 to 100, the difference runs from negative 100 to positive 100, and the zero line is simply the point where the two ages are equal. A positive value means the window’s high is more recent than its low. A negative value means the reverse.

The step size carries over as well. Since each component moves in fixed increments of 100 divided by the period, the difference between them moves in those same increments, so the oscillator is no more continuous than the lines it is built from. On a 25-bar setting it advances 4 points at a time in either direction.

Collapsing two numbers into one loses the distinction described above. A reading near zero on the oscillator is produced both when the two lines are high together and when they are low together, and those are opposite conditions on the chart. Anyone using the single line for a decision about a market that is going sideways has to go back to the two component lines to tell which of the two situations they are in.

Why a Time Reading Is Not an ADX Reading

The two are placed side by side constantly, and the comparison is usually framed as one being more sensitive or more complex than the other. That framing skips the difference that matters, which is that they measure different quantities.

An age reading answers the question of when the last extreme happened. A directional movement calculation answers a question about how much ground price covered and in which direction, which is what the ADX indicator measures. One is a clock and the other is a ruler, and neither is a substitute for the other in the way the usual comparison implies.

That settles which to reach for. A reader who wants to know whether the market has stopped making new extremes, and how long it has been since it last did, is asking a timing question and the age reading answers it directly. A reader who wants to know whether a move has enough behind it to be worth acting on is asking about distance travelled, and no amount of tuning the period will make a count of bars answer that.

The mistake to avoid is treating a high reading as confirmation of strength. It confirms recency, which is a smaller claim and sometimes an unrelated one.

Which Figures This Page Does Not State, and Why

Several figures that appear on every comparable are absent here deliberately. The 70 and 30 levels quoted as thresholds for a strong or weak reading, the attribution of the indicator to a named developer in 1995, and the claim that the name comes from a Sanskrit word for dawn were each stated by at least two of the five, and not one of the five gave a source for any of them.

Vendor documentation was checked for an independent statement of the parameters and none was obtainable. The two charting-platform documentation sites approached returned an access-denied response rather than a page.

The standard applied here rules out any of them: where several explanations repeat a number and no primary publication carries it, the number stays off the page. The arithmetic on this page is different in kind: it follows from the definition of the calculation and can be reproduced by anyone with a chart and a calculator, which is why the conversion table above carries no citation and needs none.

Who This Page Is Not For

This page will not supply entry rules, threshold levels to trade against, or a view on whether this indicator performs better than another one. It contains none of those, and an indicator reading does not indicate how any instrument will move next.

It will also not settle which period to use. That choice depends on how many bars a reader is willing to treat as the recent past, which is a decision about their own holding period rather than a property of the indicator, and the disagreement described at the top of this page is the reason no figure is recommended here.

The reader it suits is the one asking what the number in front of them is counting, before deciding whether that quantity is worth watching at all. Anyone at that point can apply the same question to the rest of the indicators traders reach for most, since the useful thing to establish about any of them is which quantity it actually measures.