OBJECTIVE To evaluate factors associated with residual astigmatism after toric intraocular lens implantation based on data from an online toric intraocular lens (IOL) back-calculator. METHODS This was a retrospective data review of an online toric IOL back-calculator, which allows users to input preoperative toric planning information and postoperative lens orientation and refractive results. These data were used to determine the optimal orientation of the IOL to minimize residual refractive astigmatism. Aggregate data were extracted from this calculator to investigate factors associated with relative magnitudes of residual astigmatic refractive error after implantation of toric IOLs. RESULTS A total of 3,159 validated records with an average reported postoperative refractive astigmatism of 1.85 diopters (D) were analyzed; 566 included data allowing calculation of surgically induced astigmatism. The relative magnitude of reported residual astigmatism appeared similar whether a femtosecond laser system was used or not. Significant differences relative to the use of intraoperative aberrometry were observed, as were differences by toric calculator. Higher measured surgically induced astigmatism was most associated with higher levels of reported residual astigmatism. A significant potential decrease in the mean refractive astigmatism was expected with IOL reorientation; in 1,416 cases (44.8%), the expected residual refractive astigmatism after lens reorientation was less than 0.50 D, with a mean reduction of 56% ± 31%. CONCLUSIONS When present after cataract surgery, higher levels of residual refractive astigmatism were most associated with large differences in measured preoperative to postoperative keratometry. To a lesser degree, intraoperative aberrometry was associated with lower levels. [J Refract Surg. 2018;34(6):366-371.].