A maintenance margin is the minimum amount of equity an investor must keep in a brokerage account to cover margin balances.
Under the regulatory guidance of NYSE and FINRA, an investor has to have in equity at least 25% of the total market value of the securities in the margin account. Depending on which brokerage firm the account is held, the maintenance margin requirements could be higher.
According the the Federal Reserve’s regulation titles “Regulation T,” when a trader buys on margin they must maintain key levels of equity throughout the life of the trade.
What is 'Buying on Margin' and Margin Trading?
What is a Margin Account?