To calculate the theoretical value of rights, start with the market value of common stock, subtract subscription price per share, and divide the result by the number of rights needed to buy one share plus 1. For example, if the stock price of a share is $75 and the subscription price is $65, and five rights are needed to buy one share, one right would be worth $1.66 ($75 - $65 = $10/$6 = $1.66).