Regulation T (Reg T) The Federal Reserve Board regulation that governs customer cash accounts and the amount of credit that brokerage firms and dealers may extend to customers for the purchase of securities. Investopedia Says: According to Regulation T, you may borrow up to 50% of the purchase price of securities that can be purchased on margin. This is known as the initial margin. Related Terms: Federal Reserve Board - FRB Initial Margin Margin Margin Account Regulation Fair Disclosure - Reg FD Regulation G Regulation U Regulation Z |