Magnesium (Mg)-based metallic glasses are considered as possible candidates in orthopedic implant applications. This paper aims to theoretically predict the glass-forming ability (GFA) in Mg-Zn-Ca alloy using a newly proposed thermodynamic model (PHHS), and the consistency of this model is verified through experimental analysis. PHHS is based on thermodynamic parameters such as enthalpy of chemical mixing, elastic enthalpy, and configurational entropy, thus incorporating the pivotal effects, i.e., electron transfer effects, effect of atomic size mismatch, and effect of randomness, which aid to high GFA. In essence, PHHS can be visualized as the energy barrier that exists between the transformations of random atomic structure of glass to ordered crystalline structure. When the PHHS value is more negative, the energy barrier will be high, supporting easy glass formation. Various Mg-Zn-Ca metallic glass compositions displayed almost an expected and supporting trend, where the critical diameter of the metallic glass rod increased with a more negative PHHS value. Among the predicted Mg-Zn-Ca systems, the Mg60Zn35Ca5 composition shows deviation from the expected trend. This discrepancy has been clearly elucidated using a eutectic phase diagram. In addition to the consistency of the PHHS parameter to verifying the GFA of various compositions, the unique ability of this model is to predict unexplored Mg-Zn-Ca glass-forming compositions using contour development. Thus, proving PHHS parameter to be used as an efficient tool in predicting new glass-forming compositions. © 2015, The Minerals, Metals & Materials Society and ASM International.