Bonus shares :
A company issues bonus shares by converting a portion of Shareholders' Fund into Share Capital. This is another way of rewarding the shareholders for investing in the company's business. To the extent the bonus shares are issued, the holder of shares is entitled to receive free shares from the company based on the current share holding. E.g. Say X is holding 100 shares in Company ABC Ltd. The company decides to issues bonus shares in the ratio 1:1 on Oct 15, 2009. On Oct 15, 2009, X will own 200 shares of ABC Ltd.
In case of issuance of bonus shares, the impact of such issuance is visible on its price. Exchanges usually announce a ex-date for trading securities on ex-benefit basis. On the ex-date prices are adjusted to reflect the impact of issuance of new shares.
E.g. In the above case, let us say that the stock price of one share of ABC Ltd was Rs. 1000 one day before the ex-date. Therefore on the ex-date the price of the shares would be adjusted to reflect increased capital on account of issuance of bonus shares.
The formula for adjusting share price is as under:
Ex- price = (Price of shares before ex-date X no. of shares)/no. of shares after issue of bonus shares
Therefore Ex-price = (1000 X 1) / (1 + 1) = 1000 / 2 = Rs. 500.
Stock Split :
Stock split is reduction in denomination (face value) of the shares. Shares in the past were issued in standard denominations such Rs. 10, Rs. 100, etc. Over many years with performance and growth, the share price of some of the companies has appreciated. E.g. Grasim has a face value of Rs. 10 however; the price of one share in Grasim is Rs. 2600. For small investor this may appear a little beyond his or her means to own the shares in Grasim. This problem of owning shares was more pronounced when securities were traded in lots of 50 shares and 100 shares.
Therefore to make appear the security price within the reach of small investors, the companies decide to split the stock denomination (face value). When stock denomination are split say from Rs. 10 to Re.1, the market price is adjusted in same proportion.
So if Grasim was to announce stock split from Rs. 10 to Re.1, the market price of the stock would get adjusted ( on ex-date) to Rs. 260 (say). Now the price of the security may appear affordable to a small investor. In a stock split, in the above example, if X is holding say 10 shares of Rs. 10 denomination before split would now hold 100 shares after split.