A memory controller having an improved operation speed controls a memory device including a plurality of memory blocks. The memory controller includes: a remaining count determiner configured to determine a remaining count that is a number of program and erase operations to be additionally performed in the memory device based on a program/erase count received from the memory device, a retention period calculator configured to determine a retention period based on a power-off time and a power-on time of the memory device and a read voltage determiner configured to generate a changed read voltage table based on a default read voltage table and a coefficient determined according to the remaining count, and determine a read voltage to be used in the memory device according to the retention period among read voltages included in the changed read voltage table.