Common Shares Outstanding Calculator
for Calculating Weighted Average

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The Shares Outstanding Calculator on this page will calculate the weighted average of up to 12 different stock transaction dates.

This free online calculator will calculate the weighted average for a company that changes its number of outstanding shares during the course of the time period you are interested in.

Unlike most textbooks that simply limit their examples to number of months, this calculator measures durations in number of days.

Plus, after calculating the weighted average the calculator will generate a line-by-line summary of each transaction.

Note that the results of this calculator are most commonly used for calculating the Earnings Per Share (EPS).

What is Weighted Average?

Weighted average is a calculation used to give more weight to more influential values within a data set, and lower weight to values with less influence.

As it relates to shares of outstanding stock, the weighted average calculation gives greater weight to larger numbers of outstanding shares and to longer durations, and gives less weight to smaller number of shares and to shorter durations.

Weighted Average Vs Simple Average

To illustrate the difference between simple average and weighted average, suppose a company has 10,000 shares outstanding at the beginning of the year and 20,000 shares outstanding at the end of the year. Using a simple average formula, the average number of shares outstanding would be 15,000 (30,000 ÷ 2 = 15,000).

However, if the year-end share increase was due to a stock split that occurred on December 15th of the year, the 15,000 simple average result would not accurately reflect the day-to-day average for the entire year.

The following results from the calculator on this page shows how the weighted average calculation more accurately reflects the day-to-day average of outstanding shares.

Date Range
1/1/2013 - 12/15/2013 10,000 348 95.34% 9,534
12/15/2013 - 12/31/2013 20,000 16 4.38% 877
Weighted average outstanding shares » 10,411

See how weighted average more accurately reflects the day-to-day outstanding shares during the year?

How to Calculate Weighted Average Shares Outstanding

Here are the steps to calculate the weighted average of number of shares outstanding based on durations stated in number of days:

  1. Count the total number of days from the beginning date to the ending date. If the total duration is a full calendar year (January 1 - December 31), then the total number of days would be 365 (or 366 for leap years).
  2. For each period containing a different number of outstanding shares, count the number of days in the period (column C in example) and divide that result by the total number of days (results in column D expressed as percentages).
  3. For each period, multiply the decimal result arrived at in step #2 by the number of shares outstanding during the applicable timeframe (results in column E above).
  4. Add up all of the results arrived at in step #3 (sum of column E in example). That sum is then equal to the weighted average number of outstanding shares.

Note that if you find yourself trying to calculate weighted average manually, it will be easier -- though less accurate -- to work with durations stated in months. In that case you would divide the number of months in each change in outstanding shares by the total months in order to arrive at the percentages in column D above.

With that, let's use the Shares Outstanding Calculator to calculate the weighted average number of shares outstanding for up to 12 stock transaction durations.

Common Shares Outstanding Calculator
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Instructions: On line #1, select the month and day and enter the 4-digit year of the starting date and then enter the beginning number of common shares outstanding.

Next, on line #13, select the month and day and enter the 4-digit year of the ending date.

Next, starting with line #2, for each stock transaction date select the month and day and enter the 4-digit year of the transaction. Then select whether the transaction added to (+) or decreased the outstanding shares (-) and enter the number of shares.

Note that all transactions must be entered in chronological order and lines that do not have a share adjustment entry will be ignored.

Finally, once all stock transaction dates and amounts have been entered, click the "Calculate Weighted Average Outstanding Shares" button.

Mouse over the blue question marks for a further explanation of each entry field. More in-depth explanations can be found in the glossary of terms located beneath the Shares Outstanding Calculator.

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Month Day Year
Adjust Shares
Outstanding Shares
1 Beginning outstanding shares:
13 Ending outstanding shares:
Help Total number of days:
Help Weighted average number of outstanding shares:
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Shares Outstanding Calculator Glossary of Terms

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Month Day Year column: Select the beginning month and day and enter the beginning 4-digit year on line #1, and then select the ending month and day and enter the ending 4-digit year on line #13. Next, beginning with line #2, select the month and day and enter the 4-digit year of each common stock transaction in chronological order (each line must have a date that is later than the line before it.

Adjust Shares column: For each common stock transaction that occurred between the beginning and ending dates, select plus (if stock issues, splits, etc.) or minus (for stock repurchases, etc.) and then enter the number of shares involved in the transaction.

Outstanding Shares column: Except for the beginning outstanding shares on line #1, all other fields in this column will automatically recalculate as you make changes to the share adjustment column.

Total number of days: This is the calculated number of days from the beginning date (line #1) to the ending date (line #13).

Weighted average number of outstanding shares: Based on your entries, this is the calculated weighted average of the shares outstanding from the beginning date (line #1) through to the ending date (line # 13).

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