Systems and methods for continually determining the remaining useful life of a drivetrain. The remaining useful life is continually determined during real-time operation of the drivetrain by determining a duty cycle based on torque and rotary speed measurements of the drivetrain. The duty cycle is converted into a useful life reduction, which is subtracted from the then-existing remaining useful life of the drivetrain. The systems and methods can additionally include displaying a remaining useful life during operation of the drivetrain, and generating an alert when the remaining useful life approaches or reaches zero. The drivetrain is optionally associated with an internal combustion engine, a wind turbine, or a gas turbine.