A system for identifying complete account identifiers from partial account identifiers is provided. The system includes an account identification computing device including at least one processor and a memory device in communication with the at least one processor. The processor is configured to receive transaction data including unique merchant identifiers, build a merchant table using the transaction data, and receive a list including partial account identifiers. The processor is further configured to determine, for each unique merchant identifier, a number of candidate account identifiers and calculate at least one metric based on the number of candidate account identifiers. The processor is further configured to identify a source unique merchant identifier and match at least one candidate account identifier to a complete account identifier by matching one of the partial account identifiers to the at least one candidate account identifier.