MACD: Line, Signal and Histogram

What MACD is built from

MACD is the difference between two exponential moving averages, usually the 12-period and the 26-period. That difference is the MACD line. Then a 9-period EMA of that line is drawn on top as the signal line. The gap between the two is plotted as bars — the histogram.

So the whole indicator is: a fast average minus a slow average, a smoothed version of that, and the distance between them. Nothing more exotic than that.

Reading each part

• The MACD line's position relative to zero tells you the fast average is above or below the slow one — in other words, whether short-term momentum is above or below longer-term momentum. Above zero is the bullish posture.
• The MACD line crossing the signal line is the classic trigger. It means the gap between fast and slow momentum has stopped widening and started closing.
• The histogram is the same information shown as a distance. Bars growing means momentum is accelerating; bars shrinking means it is fading, even before the lines cross. This is the earliest of the three readings and the reason experienced traders watch the histogram rather than waiting for the cross.

The unbounded scale matters

MACD has no fixed upper or lower limit. On a volatile market it might swing between -3 and +3; on a quiet one between -0.2 and +0.2. This means you cannot compare MACD values across different markets, and you cannot use fixed thresholds on it. A reading of +1.5 is enormous on one chart and unremarkable on another. Everything is relative to that instrument's own recent range.

Divergence: real but overused

When price makes a new high but MACD makes a lower high, momentum behind the move is weaker than it was. That is genuine information about thrust fading. But divergence can persist for a long time in a strong trend, and beginners who short every bearish divergence in an uptrend get hurt badly. Treat divergence as a warning to tighten stops and stop adding, not as a reversal trigger on its own.

The full reference with formula and parameter notes is at /indicators/macd.

How to check this yourself

Add MACD(12,26,9) to a chart and find a strong sustained move. Watch the histogram: it will start shrinking before the lines cross, and before price itself turns. That lead is the indicator's real value. Then find a choppy stretch and count how many crosses fired — that is the cost.