MACD

What is MACD?

MACD (Moving Average Convergence Divergence) is a momentum indicator built from the spread between two exponential moving averages, developed by Gerald Appel in the late 1970s. The MACD line is the 12-period EMA of price minus the 26-period EMA; the signal line is a 9-period EMA of the MACD line itself; and the histogram, added by Thomas Aspray in 1986, plots the gap between the two. The result is unbounded and scaled in price units.

The three components give three readings at different speeds. The zero-line cross is the slowest: MACD above zero simply means the 12 EMA is above the 26 EMA, a trend statement equivalent to a moving average crossover. The signal cross is faster and marks momentum turning relative to its own recent path. The histogram inflection is the earliest: shrinking bars show the spread narrowing before any cross prints.

MACD matters because it packages trend and momentum in one pane, and its line/signal/histogram grammar became the template for a whole lineage of oscillators. Its main structural limit is the price scaling: a MACD value of 2 means nothing across instruments, or across one instrument's history at different price levels, which is what percentage and volatility-normalized variants like the PPO were built to fix.

How to calculate MACD

Three EMAs and two subtractions specify the whole study; 12, 26, and 9 are the conventional defaults.

1. 1Compute two EMAs of the source (usually the close): a fast one, default 12 periods, and a slow one, default 26.
2. 2Subtract: the MACD line equals the fast EMA minus the slow EMA. Positive means the fast average is above the slow, and distance from zero measures the width of the spread.
3. 3Smooth the result: the signal line is an EMA of the MACD line, default 9 periods.
4. 4Take the difference again: the histogram equals the MACD line minus the signal line. Bars shrinking toward zero show convergence ahead of a signal cross; growing bars show the move accelerating.

How traders use it

• Signal-line crosses as momentum triggers: buying the MACD line crossing above the signal and selling the cross down. Raw crosses whipsaw badly in a trading range, so most rules add a trend or regime filter on top.
• Zero-line crosses as trend confirmation: above zero as bullish regime, below as bearish, often applied as a higher-timeframe filter that gates faster signals taken on lower timeframes.
• Histogram inflections as early warnings: the first shrinking bar after a run of expansion flags fading thrust before either cross, useful for tightening stops or scaling out rather than reversing outright.
• Divergence: price making a new extreme while the MACD line or histogram makes a lesser one is a classic regular divergence read, generally traded only with further confirmation.

MACD vs related oscillators