Methods and apparatus are provided for determining level placement in q-level cells of solid-state memory, where q>2. A group cells is read, where each cell is programmed to a respective programming level, at a series of time instants to obtain a sequence of read metric values for that cell. Statistical data as a function of time for each level is derived by processing the sequence of read metric values for the group of cells. At least one parameter of a model defining variation with time of the statistical data is determined. Calculating a set of q programming levels which has a pre-determined property over time based on a variation of the parameter as a function of level and the model.