MACD
Moving average convergence divergence plots the gap between two exponential averages. It is unbounded, which makes it a trend indicator wearing an oscillator's clothes.
MadStockAlerts Research · Updated August 28, 2026
What to take away
- The MACD line is a fast exponential moving average minus a slow one, conventionally 12 and 26.
- The signal line is a 9-period average of the MACD line.
- The histogram is the difference between the two and turns before they cross.
- It is unbounded, so there is no overbought level to read.
- It inherits every weakness of the averages it is built from.
MAD Academy Training Video · 0:45
MACD Is Two Averages Wearing a Costume
Strip the histogram away and MACD is the distance between two moving averages — which explains everything it does well and everything it does badly.
This lesson is part of a Stock Alerts + Tools plan.
Three components
MACD line = EMA(12) - EMA(26)
signal line = EMA(9) of the MACD line
histogram = MACD line - signal line
The MACD line is positive when the shorter average sits above the longer one, which is to say when recent prices are above the slightly less recent ones. Its distance from zero measures how far apart the two averages have moved, which is a direct measure of how fast the trend is running.
The histogram is the derivative of the relationship: it shrinks while the two lines converge and grows while they separate. That is why it turns before a crossing, and why it is the component most people actually watch.
Scroll the chart sideways to see all of it.
- EMA 12
How it is read
- Zero-line crossings: the fast average crossing the slow one, the same event a moving-average cross describes.
- Signal-line crossings: the MACD line crossing its own average, a faster and noisier event.
- Histogram direction: bars shrinking mean the two lines are converging, which happens before they cross.
- Divergence: price making a new extreme that the MACD line does not confirm.
The four are not independent. A histogram turning down, a signal-line cross and eventually a zero-line cross are three stages of the same underlying move, reported at increasing lag and decreasing frequency of error.
Unbounded, unlike RSI
MACD has no ceiling and no floor. A reading of 4.20 means nothing on its own; it means something only against that security's own history, because the value scales with the price and the volatility of the instrument. There is no universal overbought level and any source offering one is mistaken.
This also makes MACD readings incomparable between securities. A $500 stock produces MACD values an order of magnitude larger than a $12 stock with identical percentage behaviour, which is why the indicator is almost never used as a cross-market screen the way RSI is.
Where it fails
It inherits every weakness of the averages it is built from. In a sideways range the two averages sit on top of each other, the histogram flips sign constantly, and every crossing looks like an event.
It is a trend tool and it behaves badly when there is no trend, which is exactly the condition ADX exists to identify. Pairing a trend indicator with a measure of whether a trend is present is the standard response, and it is more useful than adjusting MACD's own parameters.
The histogram, and what it is really showing
The histogram is the difference between the MACD line and its signal line, which makes it a second derivative of price: the rate of change of the difference between two averages of the rate of change. Each layer of differencing amplifies noise, which is why the histogram is the most responsive and the least reliable of the three components.
Its conventional use is to anticipate a crossover: the histogram shrinking toward zero means the two lines are converging, and it reaches zero exactly when they cross. That is arithmetic rather than prediction, and it is the entire content of the claim that the histogram leads the signal.
The default settings of 12, 26 and 9 come from a period when a trading week was six days, and they have been carried forward unchanged for decades. There is nothing special about them beyond the fact that a great many people use them.
Because MACD is unbounded, its absolute values are not comparable across securities or across time for the same security. A reading of 2 means something different on a $30 stock than on a $300 one, which is why the shape and the crossings are read rather than the level.
Divergence, and how much weight it carries
Divergence is the observation that price made a new extreme and the indicator did not. It is among the most cited chart observations and among the weakest, for a reason that follows directly from how the indicator is built.
MACD is a difference between two averages, so it measures the rate of change of the trend rather than its level. A trend that continues while decelerating produces a divergence automatically. Deceleration is not reversal, and most trends decelerate several times before they end.
The consequence is a very high false-positive rate. Divergences appear repeatedly through a sustained trend, each one accurate about the deceleration and wrong about the reversal, and only the last one in a sequence is remembered.
The observation is not worthless. It says that the trend is slowing, which is a real description, and it carries more weight when it coincides with something independent of price: a level, a change in volume, or a failure to make a new high at all. On its own it is one view of one series.