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Moving Averages, Explained
What a moving average is, how it's calculated day to day, and how a fast (20-day) and slow (50-day) average behave differently on the same chart.
A moving average turns a noisy price chart into one clean, easy-to-read line.
How a moving average works
A moving average takes a stock's closing prices over a set number of recent periods and averages them into a single number. That number updates — or 'moves' — every time a new period closes, which smooths out day-to-day noise and makes the underlying trend easier to see.
A worked calculation
A simple 5-day moving average on five closing prices: $48, $50, $49, $52, $51.
| Sum of 5 closes | $48 + $50 + $49 + $52 + $51 = $250 |
| 5-day moving average | $250 / 5 = $50.00 |
The next day, the oldest price ($48) drops off and a new close is added in — the average recalculates using only the five most recent prices, which is what makes it 'move' over time.
Comparing a fast and slow average
| 20-day moving average | 50-day moving average | |
|---|---|---|
| How many closes it uses | 20 most recent | 50 most recent |
| How quickly it reacts to new price moves | Faster | Slower |
| How smooth the line looks | More jagged, tracks price closely | Smoother, lags further behind price |
A shorter average reacts faster because each new day carries more weight in a smaller pool of numbers. A longer average moves more slowly because any single new day gets diluted across more history. Traders often watch whether price sits above a moving average (suggesting an uptrend) or below it (suggesting a downtrend), and watch for a shorter average crossing above or below a longer one — a widely used, not guaranteed, signal.
Key takeaway: A moving average is built entirely from past prices, so it always lags a bit — the shorter the average, the less the lag, but the more it jumps around.
A 20-day and a 200-day average can even disagree on the same stock at the same time, which is normal — next, volume tells you how much conviction was behind the moves those averages are smoothing over.
This lesson is educational content explaining standard chart-reading concepts, not personalized investment or trading advice.
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