Underground hydrogen storage in porous geologic formations is a promising strategy to support the hydrogen economy by enablinglarge-scale, seasonal energy storage. However, potential geochemical interactions between hydrogen and reservoir minerals,particularly calcite, remain poorly understood. This study uses a series of kinetic simulations to explore the interactions withina hydrogen-brine-calcite system using PHREEQC software. Various experimental studies from the literature were used to tunethe models, including those on hydrogen solubility in brine and geochemical interactions with calcite. The findings indicate thatusing the default values of the PHREEQC dataset and the Van’t Hoff equation to predict the equilibrium constant for the reactionassociated with methane formation at high temperatures can be misleading, as these predictions incorrectly suggest increasedcalcite dissolution, hydrogen consumption, and methane production. To address this, a new temperature-dependent analyticalexpression for the equilibrium constant for the mentioned reaction was developed, which was calibrated against the experimentalobservations. On the basis of this experimentally calibrated model, geochemical interactions in the hydrogen-brine-calcite systemappear to be negligible at temperatures above approximately 70◦C. Although on the basis of the results of a conceptual model withlimited hydrogen availability, considerable hydrogen consumption due to geochemical reactions could occur at low temperatures(25–50◦C), the overall hydrogen loss due to dissolution in the brine is generally far less than 1% (molar). This study offers insightsinto hydrogen-brine-calcite interactions and emphasizes the need for further experimental research