Despite growing number of intraocular lens power calculation formulas, there is no evidence that these formulas have good predictive accuracy in pediatric, whose eyes are still undergoing rapid growth and refractive changes. This study is intended to compare the prediction error and the accuracy of predictability of intraocular lens power calculation in pediatric patients at 3 month post cataract surgery with primary implantation of an intraocular lens using SRK II versus Modified Formula (Pediatric IOL Calculator) for pediatric intraocular lens calculation. Modified Formula uses computer software for intraocular lens calculation. In this study, the prediction error and the accuracy of predictability of postoperative refraction in pediatric cataract surgery are comparable between SRK II and Modified Formula. The existence of the Modified Formula (Pediatric IOL Calculator) provides an alternative to the ophthalmologist for intraocular lens calculation in pediatric patients.