I was recently asked about MACD and why it is important, and this prompted me to do some research to back up my opinions. MACD, or Moving Average Convergence/Divergence, is a technical term that gets thrown around a lot. It can be a useful techinical tool to analyze a stock, and while it sounds complicated, the underlying concept is simple and really just tells you:
"What is the current trend of this stock? Is it up or down?"
"Has the stock's price trend changed directions?"
MACD is calculated by subtracting the 26-day exponential moving average (EMA) of the closing share price from the 12-day exponential moving average of the share price (don't worry about the word "exponential" for a moment). If you hold the stock you hope that the short-term average is above the long-term average. This would give a positive result and indicate that the near-term price trend is up. If the short term average is lower, the result is negative and indicates a downward trend. MACD is presented as a line around a zero axis, and even if the line is moving up, many traders do not want to buy a stock until it crosses above zero, indicating that the price trend is firmly in positive territory. Below is a chart of the share price of BASF (BF) over the last two years, with the MACD line below; the turning points in the direction of the share price are abrupt and literally appear as peaks on the line.
Mathematically, the "exponential" is calculated as follows: 2 divided by number of days in the average, e.g., for a 26 day average it would be 2/26. The exponential average formula for any one day would then be ((Current days price - Prior days average) x exponent) - current day's price. These averages are then compared over a 12 or 26 day period.
MACD is probably best used as a short term trading tool, an indicator of a good entry point. When there is a sharp valley and the line turns up, it may be time to buy. But the main disadvantages of MACD are that it is a hindsight test and that it becomes less relevant over long periods of time. For example, if BASF acquired another company, there could be a fundamental shift in its MACD rendering the past data irrelevant.