Objectives: Although hemispheric surgeries are among the most effective procedures for drug-resistant epilepsy (DRE) in the pediatric population, a large variability in outcomes remains. Identifying ideal hemispherectomy candidates is imperative to maximize the potential for seizure freedom. The objective was to develop an online, freely-accesible tool that accurately predicts the probability of seizure freedom for any patient at 1-, 2-, and 5-years post-hemispherectomy to provide clinicians accessible and reliable prognostic information to complement clinical judgement. Methods: Retrospective data of all pediatric patients with DRE and seizure outcome data from the original Hemispherectomy Outcome Prediction Scale (HOPS) study were included. The primary outcome of interest was time-to-seizure recurrence. A multivariate Cox proportional-hazards regression model was developed to predict the likelihood of post-hemispheric surgery seizure freedom duration based on a combination of variables identified by clinical judgement and inferential statistics as predictive of the primary outcome. The final model from this study was encoded in a publicly accessible online calculator on the (iNEST) website. Results: The selected variables for inclusion in the final model included the 5 original HOPS variables (age at seizure onset, etiologic substrate, seizure semiology, prior non-hemispheric resective surgery, and contralateral FDG-PET hypometabolism) and 3 additional variables (age at surgery, history of infantile spasms, and magnetic resonance (MR) imaging lesion). Predictors of shorter time-to-seizure recurrence included younger age at seizure onset, older age at surgery, prior resective surgery, generalized seizure semiology, FDG-PET hypometabolism contralateral to side of surgery, contralateral MR imaging lesion, non-lesional MR imaging, non-stroke etiologies, and history of infantile spasms. The area under the curve (AUC) of the final model was 73.0%. Significance: Online calculators are efficient, cost-free tools that can facilitate physicians in risk-estimation and inform joint decision-making with families, potentially leading to greater satisfaction. Although the HOPS data was previously validated in the first analysis, the authors encourage prospective external validation of this new tool.