The report, due Sept. 16, won't be the final word on Holmes' mental state. That's up to the jury in next year's trial.
But it will be a critical piece of evidence as jurors consider whether Holmes should be committed indefinitely to the state hospital, or whether he should be sentenced to life in prison or execution.
Holmes faces murder and attempted murder charges, and prosecutors are seeking the death penalty.
His lawyers acknowledge he was the gunman but say he was having a psychotic episode. Holmes has pleaded not guilty by reason of insanity.