We introduce pKalculator, an automated QM-based workflow that computes C-H pK a values with an MAE and RMSE of 1.48 and 1.81, respectively when correlating with experimental pK a values. We use this method to generate training data for an atom-based regression model. that delivers fast and relatively precise predictions with an MAE and RMSE of 1.24 and RMSE 2.15, respectively, when correlating with QM computed pK a values. Both methods are freely available under the MIT license. Our workflow can function as a filtering tool for computer-aided synthesis planning for the synthesis of various pK a -dependent reactions (Aldol, Michael, and Claisen), evidenced by its accurate predictions of reaction sites for 1043 reactions (MCC of 0.82). Looking ahead, we aim to explore more reactions that depend on C-H pK a values, further enhancing the utility of pKalculator for synthetic chemists. Future iterations will consider factors such as a more extensive and diverse training set, as well as steric hindrance and base reactivity, ensuring even more precise predictions for reaction sites.