Memory devices and/or methods that may estimate characteristics of multi-bit cell are provided. A memory device may include: a multi-bit cell array; a monitoring unit to extract a threshold voltage change over time value for reference threshold voltage states selected from a plurality of threshold voltage states corresponding to data stored in the multi-bit cell array; and an estimation unit to estimate a threshold voltage change over time values for the plurality of threshold voltage states based on the extracted threshold voltage change. Through this, it is possible to monitor a change over time of threshold voltages of a memory cell.