Maintenance, also referred to as "minimum maintenance" or "maintenance requirement", refers to the absolute minimum amount of equity that an investor must maintain in their margin account at all times. In the context of the NYSE and NASD, after an investor has bought securities on margin, the minimum required level of margin is 25% of the total market value of the securities in the margin account. Keep in mind that this level is a minimum, and many brokerages have higher maintenance requirements.