MACD Indicator Explained: The Lines, the Histogram, and the Signals
MACD is built from two exponential moving averages and shows how momentum is changing. Here's how the MACD line, signal line, and histogram are calculated and read.
MACD stands for Moving Average Convergence Divergence. It was developed by Gerald Appel in the late 1970s and is built entirely from exponential moving averages. It shows both the direction and the changing strength of a trend.
The Three Components
With the standard settings of 12, 26, 9:
- MACD line = 12-period EMA − 26-period EMA.
- Signal line = 9-period EMA of the MACD line.
- Histogram = MACD line − signal line.
Worked example. If the 12-period EMA is $52.40 and the 26-period EMA is $51.00: MACD line = 52.40 − 51.00 = 1.40. If the signal line is 1.10, the histogram = 1.40 − 1.10 = 0.30.
What Each Part Shows
The MACD line measures the gap between a fast and a slow average. A positive value means the faster average is above the slower one, which describes upward momentum; negative means downward.
The signal line is a smoothed version of the MACD line. It reacts more slowly, so crossings between the two lines are used as signals.
The histogram shows the distance between the two lines as bars. When bars grow, the lines are diverging (momentum increasing); when bars shrink, they're converging (momentum fading). The histogram can turn before the lines cross, so it's the earliest of the three.
The name makes sense: the lines converge and diverge.
Common Signals
Signal line crossover. MACD crossing above the signal line is read as bullish momentum; crossing below as bearish. This is the most commonly used signal.
Zero line crossover. MACD crossing above zero means the 12-period EMA has moved above the 26-period EMA, which is the same as a short-term moving average crossover on shorter periods. Crossing below zero is the reverse.
Divergence. If price makes a new high but MACD makes a lower high, momentum isn't confirming the move (bearish divergence); the reverse is bullish divergence. As with the RSI, divergences are often treated as early warnings and are easy to over-interpret.
Histogram shifts. Traders sometimes watch for the histogram to shrink toward zero as a sign that momentum is fading before a crossover.
What Makes MACD Different
Unlike RSI or the stochastic oscillator, MACD is not bounded between 0 and 100. Its values depend on the stock's price level and volatility, so a MACD reading of 2.0 means different things for a $20 stock and a $500 stock. That also means there are no fixed "overbought" and "oversold" levels; people compare current readings to the indicator's own history on that chart.
Where MACD Misleads
- It lags. Because it's built from moving averages, which are built from past prices, signals come after trends have started.
- Whipsaws. In sideways markets, the MACD line crosses the signal line repeatedly, producing many false signals.
- Settings matter. 12, 26, 9 is the default, but other settings produce different results, and there's no objectively "right" choice.
- It describes the past. A bullish crossover says momentum has increased recently, not that it will continue.
- Not comparable across stocks. The unbounded scale makes comparing MACD readings between securities misleading.
What the Evidence Says
Research testing MACD-based trading rules has produced mixed results, with performance depending on the market, period, and costs. As with other indicators, it's hard to verify claims of reliable profitability; see do chart patterns actually work.
Time Frame
A MACD crossover on a weekly chart reflects a much longer shift in momentum than one on an hourly chart. See timeframes.
This article is for educational purposes only and is not investment advice.
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