In one round of glycolysis, the net gain of ATP is 2 ATP molecules. During glycolysis, one glucose molecule 6 carbons is broken down into two molecules of pyruvate 3 carbons each . The process involves the following ATP transactions:1. Two ATP molecules are consumed in the initial steps phosphorylation of glucose to glucose-6-phosphate and conversion of fructose-6-phosphate to fructose-1,6-bisphosphate .2. Four ATP molecules are produced in the later steps two ATP molecules per each glyceraldehyde-3-phosphate converted to 1,3-bisphosphoglycerate, and then to 3-phosphoglycerate .The net gain is calculated as the difference between the produced and consumed ATP molecules: 4 ATP produced - 2 ATP consumed = 2 ATP net gain.