A stock split or stock divide increases the number of shares in a company. A stock split causes a decrease of market price of individual shares, not causing a change of total market capitalization of the company. Stock dilution does not occur. A company may split its stock, for example, when the market price per share is so high that it becomes unwieldy when traded. For example, when the share price is very high it may deter small investors from buying the shares.
Overview
For example, a company which has 100 issued shares priced at $50 per share, has a market capitalization of $5000 = 100 × $50. If the company splits its stock 2-for-1, there are now 200 shares of stock and each shareholder holds twice as many shares. The price of each share is adjusted to $25 = $5000 / 200. The market capitalization is 200 × $25 = $5000, the same as before the split. Ratios of 2-for-1, 3-for-1, and 3-for-2 splits are the most common, but any ratio is possible. Splits of 4-for-3, 5-for-2, and 5-for-4 are used, though less frequently. Investors will sometimes receive cash payments in lieu of fractional shares. It is often claimed that stock splits, in and of themselves, lead to higher stock prices; research, however, does not prove this. What is true is that stock splits are usually initiated after a large run up in share price. Momentum investing would suggest that such a trend would continue regardless of the stock split. In any case, stock splits do increase the liquidity of a stock; there are more buyers and sellers for 10 shares at $10 than 1 share at $100. Some companies have the opposite strategy: by refusing to split the stock and keeping the price high, they reduce trading volume. Berkshire Hathaway is a notable example of this. Other effects could be psychological. If many investors believe that a stock split will result in an increased share price and purchase the stock the share price will tend to increase. Others contend that the management of a company, by initiating a stock split, is implicitly signaling its confidence in the future prospects of the company. In a market where there is a high minimum number of shares, or a penalty for trading in so-called odd lots, a reduced share price may attract more attention from small investors. Small investors such as these, however, will have negligible impact on the overall price.
Currency
The analog in currency would be redenomination. This would be where a currency increases in value so that people have to use small fractions. Then a new unit can be introduced, such that an old unit is equal to 10 new units. An example is with the Australian currency. The Australian pound was split into two Australian dollars.
Effect on historical charts
When a stock splits, many charts show it similarly to a dividend payout and therefore do not show a dramatic dip in price. Taking the same example as above, a company with 100 shares of stock priced at $50 per share. The company splits its stock 2-for-1. There are now 200 shares of stock and each shareholder holds twice as many shares. The price of each share is adjusted to $25. As a result, when looking at a historical chart, one might expect to see the stock dropping from $50 to $25. To avoid these discontinuities, many charts use what is known as an adjusted share price; that is, they divide all closing prices before the split by the split ratio. Thus, when looking at the charts it will seem as if the price was always $25. Both the Yahoo! historical price charts and the Google historical price charts show the adjusted close prices.
