The metabolic pathway of the dark stage of photosynthesis, which occurs in the stroma of the chloroplasts. It is the fixation of carbon dioxide and its subsequent reduction to carbohydrate.

During the cycle, carbon dioxide combines with ribulose bisphosphate, through the mediation of the enzyme ribulose bisphosphate carboxylase, to form an unstable six-carbon compound that breaks down to form two molecules of the three-carbon compound glycerate 3-phosphate, which is converted to glyceraldehydes 3-phosphate, which is used to regenerate ribulose bisphosphate and to produce glucose and fructose.