Over the past two decades, groundwater contaminated with chlorinated organic compounds has been successfully remediated via reductive dehalogenation by zero-valent iron. While reductive defluorination of the environmentally persistent perfluorooctanoic acid (PFOA) by Fe-0 and Zn-0 is thermodynamic favorable, no successful zero-valent metal applications have been reported yet. Consequently, we developed a combined experimental-theoretical approach based on density functional theory to predict the kinetics of reductive PFOA defluorination as a function of reduction potential. The theoretical model was calibrated with experimental results for the reductive dehalogenation of the structurally similar compound tetrachloroperfluorooctanoic acid to account for the typical non-standard conditions in remedial systems, such as increased pH and metal surface passivation. Our model estimate reveals that the half-lives for the first reductive PFOA defluorination step are 8 years for Zn0 and 500,000 years for Fe0 at metal-to-water ratios typical for permeable reactive barriers. Therefore, we conclusively document that -in contrast to chlorinated solvents -reductive dehalogenation by zero-valent metals is not a viable remedial approach for PFOA unless suitable catalysts are identified.