Abstract: Systems and methods to determine on-shelf availability are provided. In example embodiments, transaction data that includes past sales transactions is accessed. A virtual time scale is determined. The virtual time scale is based on a transformation of the transaction data for a particular product category from a real-time scale to the virtual time scale that provides uniformly distributed sales. At least one estimation parameter of an exponential function based on the virtual time scale and the transaction data is determined. Using the at least one estimation parameter, current sales transaction data is monitored to detect a critical time that indicates a high probability that the particular product category will be out-of-shelf.