In response to receiving a user inquiry describing one more symptoms of a medical condition, an online hospital visit prediction system can determine whether the user will visit the hospital for treatment related to the medical condition the day following the user inquiry, termed “hospital day.” Query logs are stored for a large plurality of users. Using the query logs, a prediction model can be trained using predetermined features extracted from the query logs of each of a plurality of users for a predetermined period of time prior to the day the user visited the hospital. The predetermined features can be used to train the prediction model with a high accuracy to determine whether a future user will visit the hospital the day following a query about a medical condition.