The Calvin cycle can be described under three stages: carboxylation, reduction and regeneration.

1. Carboxylation – Carboxylation is the fixation of CO₂ into a stable organic intermediate. Carboxylation is the most crucial step of the Calvin cycle where CO₂ is utilised for the carboxylation of RuBP.

This reaction is catalysed by the enzyme RuBP carboxylase which results in the formation of two molecules of 3-A. Since this enzyme also has an oxygenation activity it would be more correct to call it RuBP carboxylase-oxygenase or RuB is CO.

2. Reduction – These are a series of reactions that lead to the formation of glucose. The steps involve utilisation of 2 molecules of ATP for phosphorylation and two of NADPH for reduction per CO₂ molecule fixed. The fixation of six molecules of CO₂ and 6 turns of the cycle are required for the removal of one molecule of glucose from the pathway.

3. Regeneration – Regeneration of the CO₂ acceptor molecule RuBP is crucial if the cycle is to continue uninterrupted. The regeneration steps require one ATP for phosphorylation to form RuBP.