Glycolysis is the process in which glucose is broken down to produce energy. It produces two molecules of pyruvate, ATP, NADH and water. Glycolysis is a two-phase process that begins in the cytoplasm of a cell. The first phase, called the investment phase, requires two ATP molecules to add phosphates to glucose. The net gain is two ATP molecules. The total number of ATP produced during glycolysis is two. The net gain of ATP produced during glycolysis is 2 molecules. While 4 ATP molecules are produced, 2 are consumed in the initial steps, resulting in a net gain of 2. 

During glycolysis, glucose ultimately breaks down into pyruvate and energy; a total of 2 ATP is derived in the process (Glucose + 2 NAD+ + 2 ADP + 2 Pi → 2 Pyruvate + 2 NADH + 2 H\(^+\) + 2 ATP + 2 H\(_2\)O).