What is the net gain of ATP during glycolysis?

The net gain of ATP during glycolysis is 2 ATP molecules. Although 4 ATP molecules are produced in the later stages of glycolysis, 2 ATP molecules are consumed in the energy investment phase (steps 1 and 3), leading to a net gain of 2 ATP per molecule of glucose. This is a small amount compared to oxidative phosphorylation but crucial for energy in anaerobic conditions.