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What Is a Moving Average? SMA vs EMA and How to Read Them

What is the difference between SMA and EMA, what do the 20, 50 and 200-day averages mean, and how are crossovers read? Common mistakes and the limits of moving averages.

What is a moving average?

A moving average is the average of a price over the last set number of candles. With every new candle the window slides one step, so the line smooths out price noise and shows the general direction.

SMA vs EMA

  • SMA (simple moving average): Gives every price in the window equal weight. It produces a slower, calmer line.
  • EMA (exponential moving average): Gives more weight to recent prices. It reacts to price faster, but also produces more false alarms.

Neither is "better". It is a trade-off between speed and stability.

Common window lengths

  • 20 days: short-term trend.
  • 50 days: medium-term trend.
  • 200 days: long-term trend. Many investors watch whether price is above or below this line.

How to read them

  1. Price relative to the average: Price above the average reads as an uptrend, below it as a downtrend.
  2. Slope: The direction of the average hints at the strength of the trend.
  3. Crossovers: A short average crossing above a long one suggests momentum is strengthening, crossing below suggests it is weakening. These are widely recognised patterns, but on their own they are not conclusive.

Common mistakes

  1. Using them in a sideways market: When price oscillates in a range, the averages keep crossing and produce many false signals.
  2. Forgetting the lag: A moving average is computed from past prices, so it shows turning points late.
  3. Ignoring costs: Rules that cross often mean many trades. See Commissions and slippage in backtests.
  4. Over-tuning one setting: Picking the window that best fits the past leads to overfitting. See the Backtesting and paper trading guide.

How it relates to other indicators

MACD is derived from moving averages: What is the MACD indicator? For momentum, also see the RSI indicator.

Remember

A moving average is a summary of past data, not a forecast. Before using a rule with real money, test it with costs and validate it in a virtual portfolio.

This article is educational and not investment advice. Past results do not guarantee future results; trading carries a risk of loss.