A system comprising a database comprising authorization data and clearing data from transactions carried out at a plurality of merchants over a payment network, the authorization data comprising a plurality of transaction records, each transaction record comprising a payment card identifier, a merchant identifier, a transaction identifier, a time and date, and an authorization transaction amount; the clearing data comprising a plurality of transaction identifiers and a corresponding plurality of clearing transaction amounts. The system also comprises a gratuity calculation component in communication with the database. The gratuity calculation component is configured to: generate, from the authorization data and the clearing data, a table of matched transaction identifiers by comparing at least a subset of the transaction identifiers of the transaction records to the plurality of transaction identifiers of the clearing data; and for the matched transaction identifiers, generating gratuity data by computing respective differences between the corresponding clearing transaction amounts and authorization transaction amounts.