An extra commission or fee that a brokerage may assess for executing an odd-lot order. An odd-lot order is an order to buy or sell a security in a quantity other than some multiple of 100. It especially refers to orders for fewer than 100 shares. Odd-lot orders are difficult to match, and a brokerage may charge an extra fee for doing so. The differential may be waived at the brokerage's discretion or under certain circumstances.
The extra markup on odd-lot purchases and markdown on odd-lot sales to compensate the brokerage firm or specialist for dealing in less than round-lot transactions. The differential usually does not apply to odd-lot executions on market opening or to odd lots submitted with round-lot orders for the same security (that is, 260 shares). Also called differential. See also basis price, with or without.