Common periods: 9, 20, 50, 100, 200

The numbers everyone watches

You can set a moving average to any period you want — 7, 13, 47, 365. But in practice, almost every trader watches the same handful of numbers: 9, 20, 50, 100, and 200. There's nothing mystical about these. They became standard because enough people use them that price often reacts to them. That reaction is part habit, part math, part self-fulfilling.

The short ones — 9 and 20 — are fast. A 9 EMA reacts quickly to recent candles, so it sits close to price during a trend. Day traders and scalpers lean on the 9 and 20 to time entries and to see when momentum is shifting. The cost of being fast is more noise: short MAs whipsaw in choppy markets.

The medium ones — 50 and 100 — are the swing-trading workhorses. The 50 SMA is the most-referenced intermediate-trend line on stock charts. Big funds use it as a default 'is this still trending' check. Price holding above the 50 SMA on a daily chart is shorthand for 'this trend is intact.' The 100 sits between the swing view and the long-term view.

The long one — 200 — is the institutional reference. The 200 SMA and 200 EMA on a daily chart are the most-watched lines in the world. Trading above the 200 daily is a common rough definition of 'bull market.' Trading below it is rough shorthand for 'bear.' We'll spend the next lesson entirely on why this line matters more than the others.

Recap: 9 and 20 for speed. 50 and 100 for swing trends. 200 for the big-picture bull/bear line. They're standard because everyone uses them — which is exactly why they matter.