Exponential Moving Average
A moving average that weights recent prices more heavily than older ones.
Also called: ema
Written by Javier Sánchez Ros
In plain language
An EMA applies exponentially decaying weights, so the most recent closes matter most and old data fades rather than dropping out abruptly.
The practical effect is that it turns faster than a simple moving average of the same length. That is an advantage in a trending market and a liability in a choppy one.
Common lengths — 9, 21, 50, 200 — are conventions, not discoveries. Their usefulness comes partly from how many people watch them.
Worked through
EMA and SMA on the same sharp reversal
- Price drops
- $64 → $58 in three bars
- 20-period EMA
- turns down on bar 2
- 20-period SMA
- turns down on bar 4
- If price recovers
- EMA whipsaws first
The EMA weights recent bars more heavily, so it reacts sooner — two bars sooner here. On a genuine reversal that is a real advantage, and it is the entire case for using one.
The same property is the disadvantage. When the drop is noise rather than a turn, the EMA has already signalled and has to reverse again, while the slower average never moved. Responsiveness and false signals are not two separate traits to be optimised independently; they are the same trait seen from two sides.
Which is why "which is better" has no answer in the abstract. A trend follower holding for weeks is usually better served by the average that ignores a three-bar shock; an intraday trader working short moves cannot afford to learn about a reversal four bars late.
The one thing that is always wrong is switching between them because the other one would have looked better on the last trade. That is not a choice of tool, it is a way of never having one.
Why it matters
The choice between EMA and SMA is really a choice about responsiveness versus false signals. Neither is better in the abstract; they suit different conditions.
Common mistakes
- Assuming a faster average is a better average.
- Switching between EMA and SMA depending on which currently supports the position you already hold.
Keep exploring
These concepts are connected. Understanding one usually makes the next one easier.
The average price over a set number of periods, recalculated as each new period closes.
A momentum indicator built from the difference between two exponential moving averages.
A sustained directional bias in price, built from a repeating pattern of highs and lows.
When price makes a new extreme but the indicator does not, suggesting momentum is fading.
A period where price moves sideways in a narrow range without clear direction.