DNA methylation has been studied extensively in many developmental systems. Little attention, however, has been given to identifying methylation features that distinguish loci whose patterns are in flux in a given cell lineage from those whose patterns are stable. Here, we develop a new metric, the Ratio of Concordance Preference (RCP), to quantify and compare epigenetic flexibility and stability across loci, cell types, and developmental stages, without assuming any specific biochemical mechanisms. We apply RCP to double-stranded DNA methylation data from human and murine cells and conclude that: (i) preference for concordant DNA methylation is reduced but not eliminated in stem relative to differentiated cells; (ii) cellular differentiation is characterized by increasing preference for concordant methylation states; and (iii) while concordance preference remains substantial through embryonic totipotency and early stages of pluripotency, primordial germ cells initially have nearly no preference for concordance, perhaps reflecting the high level of epigenetic flexibility en route to production of gametes. The mechanism-free nature of RCP will enable comparison of DNA methylation systems not only across cell types and developmental stages, but also across organisms whose methylation machineries are not well understood or may differ significantly.