MACD

MACD measures the gap between a fast and a slow moving average — it is built entirely from past prices, so it confirms moves rather than predicting them.

MACD stands for Moving Average Convergence Divergence. It is a momentum indicator built from exponential moving averages (EMAs) — averages of past closing prices that give more weight to recent prices. MACD has three parts, and it is worth defining each one precisely before talking about what they show.

The three parts, defined

• MACD line = the 12-period EMA minus the 26-period EMA. This is the gap between a faster average and a slower one.
• Signal line = a 9-period EMA of the MACD line itself. It is a smoothed, slower version of the MACD line.
• Histogram = the MACD line minus the signal line, usually drawn as bars. It shows how far the two lines are apart and whether that gap is widening or narrowing.

What each part shows

The MACD line measures the distance between the fast and slow averages, which is a read on the momentum of the recent trend. When the fast average is pulling away above the slow one, the MACD line is positive and rising; when the fast average drops below the slow one, the MACD line goes negative.

The zero line marks where the 12-period and 26-period EMAs are exactly equal. The MACD line crossing zero is just another way of saying the fast and slow averages have crossed each other.

The most commonly watched events are crossovers of the MACD line and the signal line. A crossover happens when the faster MACD line moves through its own smoothed signal line. The histogram makes the same information visual: it is zero at the moment of a crossover and grows as the two lines separate.

Divergence between MACD and price is another watched pattern: price makes a new high or low while MACD does not follow, which is read as the momentum behind the move fading. As with any divergence, it can persist for a long time without resolving.

Worked example: a bullish crossover

Suppose a stock has been drifting down and then starts to recover. As the recent prices firm up, the 12-period EMA rises faster than the 26-period EMA, so the MACD line climbs. When the MACD line rises through the signal line from below, that is a bullish crossover, and the histogram flips from negative to positive at that point.

Here is what that crossover does and does not tell you. It does tell you that recent momentum has improved enough that the fast average has caught up to and passed the slower one — a fact about price action that has already happened. It does not tell you the stock will keep rising. Because every input is a past price run through an average, the crossover only registers after the move that produced it is already underway. It confirms a shift in recent momentum; it does not forecast the next one.

Why MACD lags

MACD is a lagging indicator by construction. Moving averages smooth price by blending in older data, and subtracting one average from another does not remove that lag. The smoothing that makes MACD readable is the same smoothing that makes it late. The trade-off is most painful in choppy, sideways markets: when price drifts back and forth without a real trend, the MACD line and signal line cross each other repeatedly, producing a string of crossovers that reverse almost as soon as they appear. This back-and-forth is called whipsaw.

Honestly stated: MACD is widely used and easy to read, but it is best understood as a description of recent price momentum, not a forecasting system. For the oscillator it is often paired with, see RSI; for the underlying averages it is built from, see moving averages.

Educational only — not investment advice. Options involve a substantial risk of loss and are not suitable for every investor.