What it is
The EMA is a moving average where the most recent days carry more weight than the oldest ones. As a result, the EMA line reacts faster to price changes than an SMA of the same period.
Why people use it
A 50-day SMA equally averages 50 days. A 50-day EMA gives extra weight to today and yesterday, less to a month ago. If you want a smoothing line that turns more quickly when price changes direction, EMA is the standard tool.
Common windows
- EMA-9 — very short-term; used as the signal line inside MACD
- EMA-12 / EMA-26 — the two periods that build the MACD line itself
- EMA-50, EMA-100, EMA-200 — medium- and long-term smoothings often shown on chart platforms
The weighting trick
Today's EMA = (today's close × k) + (yesterday's EMA × (1 − k)), where k = 2 / (N + 1). For a 10-day EMA, today's close gets a weight of about 18%; everything before is folded into the prior EMA. There's no neat "sum and divide" formula — it's a rolling, weighted update.