Twice the Usual Trading Volume: Which Average Is the Baseline?
Learn to calculate a volume moving average and compare it with current volume. Explore inclusion of the current day, intraday timing differences, and how one high-volume day raises the baseline.
A volume moving average adds the volumes of a specified set of bars and divides by the number of bars. To assess whether current trading is more active than usual, first check whether the current value is included in the average. An increase in volume alone does not imply an upward direction or net inflows of new money.
Including the current bar also moves the baseline
If the aim is to compare today’s volume with a historical average, using only previously completed trading days in the denominator’s average is a clear approach. A chart’s default moving average, however, may include the current bar and update continuously. If today’s volume surges, the comparison average rises too, making the volume multiple look smaller. What matters is whether the question and formula align, rather than which approach is inherently correct. Specifying the included window, such as “relative to the average of the previous 20 trading days,” makes the number’s meaning clear.
Intraday cumulative volume and completed daily volume are not a fair comparison
Comparing volume accumulated by morning with a historical full-day average ignores the trading time still remaining. Simply extrapolating proportionally to a full day on the assumption that trading patterns are constant through time can also create large errors. If historical cumulative volume at the same time is available, use it for comparison; otherwise, label the reading as a provisional intraday value. Even when comparing yesterday’s full day with today’s full day, check for trading halts or differences in session length. Do not mix shares, contracts, and trading value as comparison units.
How long a single surge changes the average
While a one-off high-volume day remains in the moving average, ordinary trading can appear below average. When that large value leaves the window, the average can plunge even though new trading has not increased. Keep daily bars beside the average line and examine the largest day’s share of the total to identify this effect. If the mean alone makes typical conditions hard to judge, compare other statistics, such as the median, under separate labels. Around stock splits or changes in shares available for trading, the economic meaning of the same share volume can change, so also review trading value and share turnover.
Worked example
Hypothetical example: Volume was 100 shares on each of the previous four trading days and is 500 shares today. That is 5 times the average of those four days, but the 5-day average including today is (400+500)÷5=180 shares, so current volume is about 2.78 times that average. Both expressions can be calculated, but they do not mean the same thing. The example also shows why the average remains elevated until the 500-share day drops out, even if subsequent volume returns to 100 shares.
What to check
- State whether the current bar is included.
- Compare intraday cumulative volume with data from the same time of day.
- Check for one-off high-volume days inside the average.
- Check volume units, stock splits, and share-count changes.
Sources and primary materials
This is educational material about research methods. For an actual company decision, verify the filings and primary sources for the relevant period.