Regulation T
Personal Finance
Regulation T is the Federal Reserve Board rule that governs how much you can borrow through your margin account to cover the purchase price of a security. This initial margin is 50% of the total cost.
The New York Stock Exchange (NYSE) and NASD additionally require your account to have a minimum margin of $2,000 or the full cost of the purchase, whichever is less, at the time you trade, plus a maintenance margin of at least 25% of the total market value of the securities in your account at all times. Individual broker-dealers may and often do require higher minimum and maintenance margins.