MACD explained: the signal line, the zero line and the cross
MACD is two moving averages arguing with each other. See how it is built, what a bullish cross means, and what it cannot promise.
Key takeaways
- MACD is the 12-day average minus the 26-day average; the signal line is its own 9-day average.
- A cross of MACD above its signal line reads as momentum turning up, not as a promise of higher prices.
- The same cross can behave differently inside a strong downtrend, which is why some rules add a trend filter.
- Test the rule on paper, with charges, before trusting it.
How MACD is built
MACD starts with two exponential moving averages of price: a fast one over 12 periods and a slow one over 26. Subtract the slow one from the fast one and you get the MACD line. When the fast average is above the slow one the line is positive; when it is below, negative.
Then take a 9-period average of the MACD line itself. That is the signal line, and it smooths the noise. The gap between the two lines is drawn as bars called the histogram.
Reading the zero line and the signal line
The MACD line against zero shows the direction of the trend. The MACD line against its signal line shows whether momentum is picking up or fading. When the histogram turns positive, the MACD line has crossed above its signal line.
The bullish cross, with Stock A
Suppose Stock A has been drifting down for weeks, so its MACD line sits below its signal line and below zero. Then the line curls up and crosses above the signal line. That crossing is called a bullish cross. It reads as downward momentum running out of steam. It is not a promise that price goes up next.
Why some rules add a filter
A cross in the middle of a strong downtrend can behave differently from one after the trend has already turned. In SmartPaperDesk, the MACD Bullish Cross strategy uses only the cross: the MACD histogram moving above zero. A separate strategy, MACD Trend Filter, takes the cross only while price is above a longer-term average. Open either card to read its exact rule.
What MACD cannot do
MACD is built from past prices, so it lags. In a sideways market it crosses back and forth and produces many false starts. It says nothing about value, and it cannot promise a result.
Test a MACD rule on paper
Write the rule down, test it on historical daily data with estimated charges and a stop, and compare the number of trades and the worst dip, not only the final number. You can do this on the SmartPaperDesk free plan with no real money.
Questions people ask
What do 12, 26 and 9 mean in MACD?
12 and 26 are the periods of the fast and slow moving averages. 9 is the period of the signal line, an average of the MACD line itself.
Is a MACD bullish cross a buy signal?
No. It suggests momentum is turning up, but it can fail, especially in a strong downtrend or a sideways market. Test any rule before trusting it.
Test a MACD rule on the free plan
Keep reading
SmartPaperDesk is an educational paper-trading tool. Examples use a made-up Stock A.
For educational purposes only. This is not investment advice. Past performance does not guarantee future results.