SMA vs. EMA: What's the Difference?

Both are ways of smoothing jumpy prices into one trend line by averaging the recent past. The SMA treats every day in its window equally, while the EMA gives recent days extra weight, so it reacts faster when price changes direction. The choice is a trade: steadiness versus speed.

An SMA is the plain average of the last N closing prices, each day counting the same, while an EMA re-weights the window so the newest prices matter most and older ones fade. The EMA stays close to price and turns earlier, which helps for shorter-term decisions but also gets it fooled by brief moves that quickly reverse. The SMA is slower and calmer, missing the first stretch of every real turn but ignoring most of the noise. The best-known example is the 200-day SMA, which many investors treat as a dividing line: price above it counts as a healthy market, price below it as a weak one. So many people watch that line that it partly enforces itself. Traders often run a fast and a slow average together, which is where crossover signals such as the golden cross come from. Neither average predicts anything; both describe the past.

An online seller's star rating, computed two ways: one averages every review ever left, the other counts the last month's reviews extra. New management takes over the shop, and the recency-weighted score jumps within weeks while the all-time average takes months to notice. Neither is wrong — one answers what the shop is like now, the other what it has reliably been.