An important goal in building our model was to be able to predict uncertainties which actually provide some guidance as to expected accuracy and limitations in the training data. Not all commercial products make this a priority; for example, SimulationPlus did not provide uncertainty estimates for any of their predictions. One obvious feature in our data is that the predicted uncertainties are all very large, greater than 1 pK a unit for 19 of the matched predictions. Most of the molecules with large uncertainties are polyprotic and include functional groups outside the domain of our training set. Therefore it seems these large uncertainties are a good sign as they seem to correlate with actual error.