In calcareous parent material, pedogenic carbonate formation mostly involves dissolution and recrystallization of lithogenic carbonates with CO₂ of soil air, leading to a complete exchange of lithogenic carbon with soil-derived carbon. Interest in pedogenic carbonates has increased in recent decades because they are a useful tool for reconstructing paleoclimatic conditions (δ¹³C and δ¹⁸O) and past atmospheric CO₂ concentrations as well as for radiocarbon dating of soils. For such investigations, the recrystallization rate of primary CaCO₃ by pedogenic carbonate formation and the dependence of the recrystallization rate on environmental factors are essential, but still unquantified factors. The recrystallization rate of primary CaCO₃ of loess at three CO₂ concentrations was estimated by isotopic exchange between primary CaCO₃ and the ¹⁴C of artificially labeled CO₂. Loess was used for the study as a parent substrate for soil formation to simulate initial rates of CaCO₃ recrystallization. CO₂ concentrations of 380 ppm, 5000 ppm and 50,000 ppm lead to recrystallization rates of 4.1·10⁻⁷ day⁻¹, 8.1·10⁻⁷ day⁻¹ and 16.9·10⁻⁷ day⁻¹, respectively. The relation between CO2 concentrations and recrystallization rates was described by a saturation curve. Under the tested experimental conditions, complete (95%) recrystallization of loess carbonate and formation of pedogenic carbonate would take 4.9–20.0·103 years, strongly depending on CO₂ concentration. We expect faster recrystallization rates under field conditions because of permanent CO₂ supply by root and rhizomicrobial respiration. This impedes the equilibrium between the inorganic C pools in solid, liquid and gaseous phases.