The maximum takeoff mass (MTOM) or maximum gross takeoff mass (MGTOM)of an aircraft is the maximum mass at which the pilot is allowed to attempt to take off, due to structural or other limits. The analogous term for rockets is gross lift-off mass, or GLOM. MTOM is usually specified in units of kilograms or pounds.

MTOM is the heaviest weight at which the aircraft has been shown to meet all the airworthiness requirements applicable to it. MTOM of an aircraft is fixed and does not vary with altitude, air temperature, or the length of the runway to be used for takeoff or landing. A different weight, the "maximum permissible takeoff mass" or "regulated takeoff mass", varies according to flap setting, altitude, air temperature, length of runway and other factors. It is different from one takeoff to the next, but can never be higher than the MTOM.

Regulated Take-Off Mass (RTOM) is the lowest of the ’performance limited’ and ’structural limited’ TOM.