According to one embodiment, a memory system includes a nonvolatile memory and a memory controller. The memory controller is configured: to store, in a buffer, a data set read from a cell unit, and an expected data set generated by an error correction on the data set; to count a number of first and second memory cells corresponding to a first and a second combination of data in the data set and the expected data set, respectively, among the memory cells in the cell unit; to calculate a shift amount of a read voltage used in a read operation from the cell unit, based on the number of the first and second memory cells; and to apply the shift amount to a next read operation from the first cell unit.