In method of programming a nonvolatile memory device, multi-bit data are loaded into a plurality of page buffers. Multi-level cells included in a multi-level cell block are programmed to a plurality of intermediate program states including a first intermediate program state and a second intermediate program state which is higher than the first intermediate program state based on the multi-bit data. Whether the multi-level cells are programmed to the plurality of intermediate program states is verified. Cell group information for the first intermediate program state is generated by checking whether a result of the verification for the second intermediate program state satisfies a predetermined criterion. The multi-level cells are programmed to a plurality of target program states corresponding to the multi-bit data based on the cell group information.