1.307-1—General.

(a) If a shareholder receives stock or stock rights as a distribution on stock previously held and under section 305 such distribution is not includible in gross income then, except as provided in section 307(b) and § 1.307-2, the basis of the stock with respect to which the distribution was made shall be allocated between the old and new stocks or rights in proportion to the fair market values of each on the date of distribution. If a shareholder receives stock or stock rights as a distribution on stock previously held and pursuant to section 305 part of the distribution is not includible in gross income, then (except as provided in section 307(b) and § 1.307-2) the basis of the stock with respect to which the distribution is made shall be allocated between (1) the old stock and (2) that part of the new stock or rights which is not includible in gross income, in proportion to the fair market values of each on the date of distribution. The date of distribution in each case shall be the date the stock or the rights are distributed to the stockholder and not the record date. The general rule will apply with respect to stock rights only if such rights are exercised or sold.
(b) The application of paragraph (a) of this section is illustrated by the following example:

Code of Federal Regulations

Example. A taxpayer in 1947 purchased 100 shares of common stock at $100 per share and in 1954 by reason of the ownership of such stock acquired 100 rights entitling him to subscribe to 100 additional shares of such stock at $90 a share. Immediately after the issuance of the rights, each of the shares of stock in respect of which the rights were acquired had a fair market value, ex-rights, of $110 and the rights had a fair market value of $19 each. The basis of the rights and the common stock for the purpose of determining the basis for gain or loss on a subsequent sale or exercise of the rights or a sale of the old stock is computed as follows: 100 (shares)×$100=$10,000, cost of old stock (stock in respect of which the rights were acquired). 100 (shares)×$110=$11,000, market value of old stock. 100 (rights)×$19=$1,900, market value of rights. 11,000/12,900 of $10,000=$8,527.13, cost of old stock apportioned to such stock. 1,900/12,900 of $10,000=$1,472.87, cost of old stock apportioned to rights. If the rights are sold, the basis for determining gain or loss will be $14.7287 per right. If the rights are exercised, the basis of the new stock acquired will be the subscription price paid therefor ($90) plus the basis of the rights exercised ($14.7287 each) or $104.7287 per share. The remaining basis of the old stock for the purpose of determining gain or loss on a subsequent sale will be $85.2713 per share.