This study was aimed to assess the predictability of intraocular lens (IOL) power calculation after simultaneous pterygium excision and phacoemulsification with IOL implantation. We retrospectively reviewed the clinical charts of 60 eyes of 60 consecutive patients (mean age ± standard deviation, 73.5 ± 7.0 years) who developed pterygium and cataract. We determined visual acuity (logMAR), manifest spherical equivalent, manifest astigmatism, corneal astigmatism, and mean keratometry, preoperatively and 3 months postoperatively. Corrected visual acuity was significantly improved from 0.19 ± 0.20 preoperatively to −0.06 ± 0.07 postoperatively (P < 0.001, Wilcoxon signed-rank test). Uncorrected visual acuity was also significantly improved from 0.62 ± 0.33 preoperatively to 0.31 ± 0.32 postoperatively (P < 0.001). At 3 months, 48% and 82% of the eyes were within ± 0.5 and ± 1.0 D, respectively, of the targeted correction. We found significant correlations of the prediction errors with the changes in the mean keratometry (Spearman signed-rank test, r = −0.535, P < 0.001) and with the pterygium size (r = −0.378, P = 0.033). Simultaneous pterygium and cataract surgery was safe and effective, and the accuracy was moderately predictable. However, it should be noted that a significant myopic shift occurred postoperatively, possibly resulting from the steepening of the cornea after pterygium removal, especially when the size of pterygium was large.