as always, you've to apply the proper analysis tool the appropriate market. Not every stock has made 50% move before MACD turns.
MACD has been developped as a mediumterm, trendfollowing system.
The default settings work well for a variety of markets and stocks -
But MACD crossover Signals are simply to slow for highly volatile issues.
In case you want to apply MACD on highly volatily issues, you'd better trade it's histogramm signals than it's crossovers.
The MACD histogram displays the differences between the MACD and it's trigger line ( i.e the 9 period MA in def. setting ) in form of bars.
The lenght of the bar is equivalent to the difference between MACD + it's triggerline. Bars above the 0 centerline indicate, that MACD is above zero and vice versa.
One can trade 2 types of signals with the histogram :
1. Crossovers through the centerline ( slower )
2. Reversals in bars ( faster ) = not necessarily identical with a crossover of the MACD and it's triggerline
The rules are plain and simple :
MACD Hist. above 0 :
Buy when last bar is higher than previous bar
Sell when last bar is lower than previous bar.
MACD Hist below 0:
Buy when last bar is shorter than previous bar ( rise towards the zero line )
Sell when last bar is longer than previous bar ( rise away from 0 line )
For trading a reversal, a trader waits until the histogram built a top ( below or above centerline ) and starts to retreat in the opposite direction.
As an example, have a view to this chart of LLTC, certainly one of the higher volatile stocks
http://stockcharts.com/def/servlet/SC.web?c=LLTC
Here you can see the MACD in def. settings and it's historgam.
When you compare now, how the Histogram bars react to the stocks price movement, it will become clear, how to trade these signals.
Tinkering arround with different settings is not really adding value, but there are some traders who suggest to use i.e.
5 / 38 / 7 periods settings - but then again, these settings may not work for a number of other stocks.
A better way to apply MACD is to use it in conjunction with other, faster indicators.
Since the MACD reacts slowly to very fast price changes, one should either use the histogramm - which is definitely fast aur apply i.e. an 8,3,3 or 14,3,3, Stochastic in addition to MACD.
Elder's triple screen system looks i.e. for a weekly MACD to determine the trend and a daily Stoch or RSI to determine entry signals - which are only taken in the direction of the weekly trend.
Hope this helped a bit