Authoritative information regarding grades and grade point averages is published under Rules & Regulations V in the Catalog.
Catalog: Rules & Regulations V: Grades/Average
Rules & Regulations V explains the requirements for midterm progress reports:
Progress report grades are submitted to the Office of the Registrar for all classes numbered 1000 and 2000 in the Fall Semester and Spring Semester. These grades are used for advising students, not for calculating any grade-point average (GPA) at Georgia Tech. Progress report grades are "S" or "U." A grade of "U" indicates that, based on the work completed to that point in the academic term, the student's standing is in the "D" or lower range. Progress report grades must be submitted once 40 percent of the academic term has passed, as specified by the official Academic Calendar. The due date for reporting will be noon on Monday and the grades will be available to students that afternoon.