A stock split does not change the ownership percentage of investors. A stock split is simply an increase of shares outstanding by a set multiple. However, dilution is "a reduction in the ownership percentage of a share of stock caused by the issuance of new stock. Dilution can also occur when holders of stock options (such as company employees) or holders of other optionable securities exercise their options. When the number of shares outstanding increases, each existing stockholder will own a smaller, or diluted, percentage of the company, making each share less valuable. Dilution also reduces the value of existing shares by reducing the stock's earnings per share." ( http://www.investopedia.com/terms/d/dilution.asp )
ex. If 10 people own 2 shares each of a company (100% of the available shares) and 20 addition shares are authorized; the shares for the original holders has an ownership decrease of 50%.
