The evolution of conformational constraints in bisphenol-A polycarbonate (BAPC) upon quiescent bulk crystallization was quantitatively analyzed from calorimetric study employing a rigid amorphous fraction (RAF) as an indicator of the level of conformational constraints. From the correlation between corrected crystallinity (X$sub$c/) and total rigid fraction (f$sub$r/), it was found that, regardless of molar mass distribution and thermal treatment conditions, semicrystalline BAPC always exhibits greater f$sub$r/ than X$sub$c/ maintaining a quantitative relationship of f$sub$r/〓2X$sub$c/ in the range of 0.0 <X$sub$c/< 0.4. This directly indicates the evolution of approximately the same amount of RAF as X$sub$c/, (i.e., RAF〓X$sub$c/) upon bulk crystallization of BAPC. It was also found that T$sub$g/ per se and T$sub$g/ broadening enhance as RAF increases, and there appears to be a critical level of RAF (>0.2) needed to initiate significant changes in both quantities.