What Does MACD Do?

MACD measures the difference between two Exponential Moving Averages (EMAs). A positive MACD indicates that the 12-day EMA is trading above the 26-day EMA. A negative MACD indicates that the 12-day EMA is trading below the 26-day EMA. If MACD is positive and rising, then the gap between the 12-day EMA and the 26-day EMA is widening. This indicates that the rate-of-change of the faster moving average is higher than the rate-of-change for the slower moving average. Positive momentum is increasing, indicating a bullish period for the price plot. If MACD is negative and declining further, then the negative gap between the faster moving average (blue) and the slower moving average (red) is expanding. Downward momentum is accelerating, indicating a bearish period of trading. MACD centerline crossovers occur when the faster moving average crosses the slower moving average.

This Merrill Lynch (MER) chart shows MACD as a solid black line, and its 9-day EMA as the thin blue line. Even though moving averages are lagging indicators, notice that MACD moves faster than the moving averages. In this example, MACD provided a few good trading signals as well:

1. In March and April, MACD turned down ahead of both moving averages, and formed a negative divergence ahead of the price peak.
2. In May and June, MACD began to strengthen and make higher Lows while both moving averages continued to make lower Lows.
3. Finally, MACD formed a positive divergence in October while both moving averages recorded new Lows.