The memory controller may include a command generator generating and outputting first and second read commands to a memory device so that respective first and second read operations are performed using a first read voltage, a calculator receiving first and second read data in response to the read commands, comparing the first and second read data each other, and calculating a number of first inverted cells and a number of second inverted cells based on a result of the comparing, each of the first inverted cells having a bit value that inverted from a first bit value to a second bit value, and each of the second inverted cells having a bit value that inverted from the second bit value to the first bit value, and a read voltage determiner changing the first read voltage depending on the number of first inverted cells and the number of second inverted cells.