The number of shares outstanding in a company will often change due to a company issuing new shares, repurchasing shares, and retiring existing shares. The number of outstanding shares can also change if other financial instruments are turned into shares. An example of this is when employees of the company convert their employee stock options (ESO) into shares.

The weighted average of outstanding shares is a calculation that incorporates any changes in the number of a company's outstanding shares over a reporting period. The reporting period usually coincides with a company's quarterly or annual reports. The weighted average is a significant number because companies use it to calculate key financial measures, such as earnings per share (EPS), for the time period.

### Key Takeaways

- The weighted average of outstanding shares is a calculation that a company uses to reflect any changes in the number of the company's outstanding shares over a reporting period.
- Events that can cause the number of a company's outstanding shares to fluctuate include share buybacks, employees exercising stock options, the issuance of new shares, and the retirement of existing shares.
- To calculate the weighted average of outstanding shares, take the number of outstanding shares and multiply the portion of the reporting period those shares covered; do this for each portion and then add the totals together.
- It's important for a company to have an accurate weighted average of outstanding shares because the number is used to calculate key financial measurements, such as earnings per share (EPS).

## Importance of a Weighted Average of Outstanding Shares

Calculating a weighted average of outstanding shares is important because it allows a company to calculate its earnings per share (EPS), which is a measurement of how much money a company makes for each share of its stock. Potential investors in a company look at the EPS as an indicator of the company's profitability and compare this metric with the EPS of other companies before making an investment decision.

For example, let's say a company has 100,000 shares outstanding at the start of the year. Halfway through the year, it issues new shares in the amount of an additional 100,000 shares. Thus, the total amount of shares outstanding increases to 200,000.

If at the end of the year the company reports earnings of $200,000, which amount of shares should be used to calculate earnings per share (EPS): 100,000 or 200,000? If the 200,000 shares were used, the EPS would be $1, and if 100,000 shares were used, the EPS would be $2—this is quite a large range! To avoid the confusion caused by such a large range, the company must calculate the weighted average of outstanding shares to arrive at a more accurate EPS for the given time period.

## Calculating Weighted Average of Outstanding Shares

This potentially large range is the reason why a weighted average is used, as it ensures that financial calculations will be as accurate as possible in the event that the amount of a company's shares changes over time. The weighted average number of shares is calculated by taking the number of outstanding shares and multiplying the portion of the reporting period those shares covered, doing this for each portion and, finally, summing the total. The weighted average number of outstanding shares in our example would be 150,000 shares.

The earnings per share calculation for the year would then be calculated as earnings divided by the weighted average number of shares ($200,000/150,000), which is equal to $1.33 per share.

## Special Considerations

Understanding how to calculate a weighted average can also be useful to individual investors who want to calculate their cost basis. The cost basis refers to the original purchase price of an asset or investment for tax purposes. Investors calculate the cost basis to determine if their investment has been profitable or not, along with any possible taxes they might owe on the investment.

Because investors frequently purchase shares of a company at various times and in various amounts as they build their position in a stock, it can be a challenge to keep track of the cost basis of those shares. One method is for the investor to calculate a weighted average of the share price paid for the shares. The investor would multiply the number of shares acquired at each price by that price and then add those values together. Lastly, divide the total value by the total number of shares purchased to arrive at the weighted average share price.