The term "excess margin securities" refers to margin securities carried for the account of a customer having a market value in excess of 140 percent of the total debit balance in the customer's account. These securities are in excess of the securities held in a customer's margin account that are pledged by the customer as collateral for the margin loan and can be used to support the purchase of additional securities on margin

Example:

A customer whose account equity consists solely of a cash balance of USD 10,000 on Day 1 purchases 400 shares of stock ABC at USD 50 per share on Day 2.

On Day 2, the customer's excess margin securities total USD 6,000. This is calculated by subtracting 140% of the margin debit or loan balance from the market value of the stock position ($6,000 = $20,000 - {1.4 * $10,000}).

The term is relevant from a regulatory perspective as the SEC requires that U.S. broker dealers segregate and maintain in a good control location (e.g., DTC or bank) all customer securities which are deemed excess margin securities. Such securities cannot be pledged or loaned to finance the activities of the firm or other customers without specific written permission from the customer. The portion of the securities classified as margin securities ($20,000 - $6,000 or $14,000 in this example) are subject to a lien and may be pledged or loaned by the broker to others to assist in financing the loan made to the customer.

Note that securities which were excess margin at the date of acquisition may later be reclassified as margin securities based upon the customer's subsequent trade and/or margin borrowing activity. For example, if the loan value of excess margin securities is subsequently used to acquire additional securities on margin, a portion of securities will then be reclassified as margin securities and subject to a lien. If the customer subsequently deposits cash or sells securities to reduce or eliminate the margin loan, the securities will be reclassified as excess margin or fully paid and are required to be segregated.
See also "fully paid securities".