A capital surplus is the additional paid-in capital in excess of par value that an investor pays when buying shares from an issuing entity. This amount represents the difference between the market value of shares and their par value. The term is is no longer commonly used; instead, the concept is now called additional paid-in capital in the accounting literature.
Par value was originally the price at which a company's shares were initially offered for sale, so that prospective investors could be assured that the company would not issue shares at a price below the par value. However, par value is no longer required by some states; in other states, companies are allowed to set the par value at a minimal amount, such as $0.01 per share. The result is that nearly all of the price paid for a share of stock is recorded as additional paid-in capital (or capital surplus, to use the older term). If a company issues shares that have no stated par value at all, then there is no capital surplus; instead, the funds are recorded in the common stock account.
For example, if ABC Company were to sell 100 shares of its $1 par value common stock for $9 per share, it would record $100 of the $900 in total proceeds in the Common Stock account and $800 in the Additional Paid-in Capital account. In earlier days, the $800 entry to the Additional Paid-In Capital account would instead have been made to the Capital Surplus account.
Thus, if the capital surplus term were still used, a company would acquire a capital surplus by selling its stock to investors at a price above the designated par value of the stock, with the incremental amount above the par value being identified as capital surplus.
A capital surplus is also called additional paid-in capital or a share surplus.