MACD Histogram: A Gap Between Two Lines

Michael Whitman · Trading since 2017, full-time since 2020 · Reviewed 2026-09-06

The MACD histogram plots the distance between the moving average convergence divergence line and its own nine-period signal line. Shrinking bars mean those two lines are converging, which is a statement about the indicator rather than about the direction of price.

How it works

A candlestick chart of the site's shared price history. The headline on the chart reads: The bars are the gap between two lines. — The bars are the gap between two lines. Illustrative chart - not real market data.

The MACD indicator has two lines. The main line is a fast exponential average minus a slow one — conventionally 12 minus 26. The signal line is a nine-period exponential average of that.

A gently rising stretch of the long price series. The headline on the chart reads: Moving average line minus its own nine-period signal. — Moving average line minus its own nine-period signal. Illustrative chart - not real market data.

The histogram is the first minus the second. Each bar is the vertical distance between the two lines at that point. Nothing else is in it.

A flat but volatile stretch of the long price series. The headline on the chart reads: It is a rate of change of a rate of change of price. — It is a rate of change of a rate of change of price. Illustrative chart - not real market data.

Count the layers and the tool’s distance from price becomes clear. Price, then two moving averages, then their difference, then a smoothing of that difference, then the gap between those two. The histogram is four transformations away from a close, and each one costs a little more responsiveness and a little more meaning.

The two readings, and what each actually says

A calmly advancing stretch of the long price series. The headline on the chart reads: Crossing zero is the same event as the two lines crossing. — Crossing zero is the same event as the two lines crossing. Illustrative chart - not real market data.

The histogram crosses zero exactly when the two lines cross. Those are not two signals. They are one event displayed two ways, and a chart showing both is showing the same information twice — worth knowing before treating agreement between them as confirmation.

A flat, quiet stretch of the long price series. The headline on the chart reads: Shrinking bars mean the gap is closing, not that price is falling. — Shrinking bars mean the gap is closing, not that price is falling. Illustrative chart - not real market data.

The second reading is bar size: growing bars mean the lines are separating, shrinking bars mean they are converging. This is where the common misreading lives. Shrinking bars are frequently described as momentum fading, which sounds like a statement about price and is a statement about two averages getting closer.

Price can rise steadily while the histogram shrinks the entire time. A trend that advances at a constant rate has a stable gap between its fast and slow averages, and any steadying at all pulls them together. Nothing is weakening; the acceleration has stopped, which is not the same thing.

A strongly rising stretch of the long price series. The headline on the chart reads: It has no fixed range, so no level means anything across time. — It has no fixed range, so no level means anything across time. Illustrative chart - not real market data.

And the histogram has no bounds. Unlike the relative strength index or the stochastic, which are scaled 0 to 100, this is in the instrument’s own price units. A reading of 0.8 means nothing on its own — not across instruments, not across timeframes, and not across different price levels on the same instrument.

In practice

A declining stretch of the long price series. The headline on the chart reads: And it moves with the relative strength index at 0.71. — And it moves with the relative strength index at 0.71. Illustrative chart - not real market data.

On this site’s shared 576-bar history, bar-to-bar changes in the histogram correlate at 0.71 with a 14-period relative strength index, 0.66 with the commodity channel index and 0.66 with 10-period momentum. It is not measuring something the rest of the oscillator family is missing.

A candlestick chart with a volume histogram beneath it, with the volume histogram emphasised. The headline on the chart reads: Nothing in the calculation knows what traded. — Nothing in the calculation knows what traded. Illustrative chart - not real market data.

Volume is absent from every layer. If you want an input that can disagree with the price side of the chart, it has to come from participation or from a different timeframe, not from another arrangement of closes.

A long-horizon candlestick view of the same price series. The headline on the chart reads: Aggregate the bars and the histogram is a different shape. — Aggregate the bars and the histogram is a different shape. Illustrative chart - not real market data.

Aggregating the chart changes the histogram completely, because 12 and 26 periods cover a different span of market. The settings are conventional, not derived, and they were chosen for a daily chart in an era of shorter trading weeks.

A candlestick series containing several opening gaps, with the largest opening gap marked. The headline on the chart reads: A gap produces the largest bar on the histogram. — A gap produces the largest bar on the histogram. Illustrative chart - not real market data.

A gap produces the biggest bars you will see. The fast average moves much more than the slow one, the gap between them widens sharply, and the histogram registers maximum momentum for a move in which nothing traded.

A declining stretch of the long price series, with the entry price and the level at which a stop would trigger drawn as horizontal lines. The headline on the chart reads: And a histogram bar is not a price to exit at. — And a histogram bar is not a price to exit at. Illustrative chart - not real market data.

It contains no price. Exiting “when the histogram turns” means exiting at whatever price happens to be trading when a derived quantity changes sign, which is not a stop and cannot be sized against.

Each zero cross traded costs a share of a bar. Illustrative chart - not real market data.

Each zero cross traded costs 2% of a typical bar’s range in round-trip costs on this history, and a histogram oscillating around zero in a quiet market crosses repeatedly.

A 72-bar candlestick section of the shared price history. The headline on the chart reads: Two smoothings subtracted is still one price series. — Two smoothings subtracted is still one price series. Illustrative chart - not real market data.

And the order book contains no histogram. Whatever the bars do, the market is not responding to them — other people watching the same conventional settings is the only mechanism available, and that is a weaker effect on a derived quantity than on a visible price level.

What the MACD histogram is not

It is not a momentum measurement of price. It measures the distance between two smoothings of price, which is a related but distinct quantity.

It is not a second signal alongside the line cross. Zero-crossings and line-crossings are the same event.

It is not comparable across charts. No fixed scale means no transferable levels.

And it is not independent of the other oscillators. 0.71, 0.66 and 0.66 against three of them on this data.

When it fails

A sideways, range-bound candlestick series. The headline on the chart reads: In a range it oscillates around zero and crosses constantly. — In a range it oscillates around zero and crosses constantly. Illustrative chart - not real market data.

In a range it oscillates around zero and crosses constantly. Every crossing looks like a signal, and the bars either side are small, so there is not even a size reading to filter them with.

The second failure is reading shrinking bars as weakness. A steady advance produces shrinking bars. Exiting on that basis means exiting trends that are behaving exactly as trends do.

A third is comparing histogram heights over time. Without a fixed scale, a bar twice as tall as last month’s says something about volatility as much as about direction.

A fourth is treating the standard 12/26/9 as meaningful. Those numbers are conventional. They were not derived from anything and they are not tuned to your instrument or timeframe.

And a fifth is the four-layer distance from price. Every transformation adds lag and removes information, and by the time you are reading the gap between a smoothing and a smoothing of that smoothing, the connection to what actually happened is thin.

The original data

Bar-to-bar change correlations on this site’s shared 576-bar history: the histogram against the relative strength index 0.71, against the commodity channel index 0.66, against 10-period momentum 0.66, against the stochastic 0.61. The full matrix — every oscillator pair, all between 0.53 and 0.87 — is in research/series-measurements.json, produced by site/measure_series.py.

A 72-bar window of the shared price history, cut short at the decision bar. The headline on the chart reads: The bars are shrinking but still positive. Exit? — The bars are shrinking but still positive. Exit? Illustrative chart - not real market data.

No pair in that matrix falls below 0.53, and that is the finding. Five oscillators built by different people at different times, from the same closes, and the least similar pair still moves together on more than half of all bars. The practical consequence is that a chart with three oscillators on it has roughly one oscillator’s worth of information and three times the screen clutter — and the way to find out which one to keep is to compute this matrix on your own instrument rather than to argue about which is best.

MACD is the indicator the histogram is derived from. MACD crossover is the event the zero line marks. And MACD divergence is the comparison most often read off these bars.

What I actually do

The histogram is the part of this indicator I used longest without understanding, because shrinking bars feel like weakness. They are not - they are two smoothed lines getting closer, which happens on the way into a turn and also happens when a trend simply steadies.

— Michael Whitman

This page is educational, not financial advice. Test every idea on your own charts before risking money.