Glycolysis invests two ATP early and forms four ATP later, giving a net gain per glucose of:

1. The first half of the pathway spends ATP to destabilise glucose. 2. The second half earns ATP back by substrate-level phosphorylation. 3. Although two molecules of ATP were invested, four molecules of ATP are formed, resulting in a net gain of two ATP and two NADH molecules for the cell. 4. Four is the gross figure, so it is the trap here. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 7 'Cellular Respiration', sections 7.1-7.7_