1. A computer implemented method for determining ranges of purchasing amounts, said method comprising: accessing purchasing data from a historical database of confirmed purchasers such that each confirmed purchaser has purchased at least one item having a non-null monetary value, wherein the historical database comprises the purchasing data for each confirmed purchaser within a historical duration that includes N consecutive generations and T consecutive cycles, wherein each generation is associated with a generation group consisting of all confirmed purchasers who have made a first purchase of an item of the at least one item within the associated generation, wherein each cycle of the T consecutive cycles is a time unit for analysis of the purchasing data for each confirmed purchaser, wherein N is at least 2, and wherein T is at least 3; determining re-purchasing ratios from the accessed purchasing data, wherein the re-purchase ratios indicate a probability of purchasing in a next cycle of the T consecutive cycles immediately following a latest cycle of the T consecutive cycles, wherein the re-purchase ratios are indexed according to generation group, latest cycle, and recency frequency class, wherein the recency frequency class is a binary descriptor of purchases over M consecutive cycles of the T consecutive cycles, wherein the M consecutive cycles end with the latest cycle, and wherein M is at least 2; determining purchasing amounts from the accessed purchasing data, wherein the purchasing amounts are indexed according to generation group, latest cycle, and recency frequency class; computing potential purchasing amounts in the next cycle by combining the re-purchasing ratios and the purchasing amounts, wherein the potential purchasing amounts are indexed according to latest cycle and recency frequency class; and outputting the potential purchasing amounts to an output device of a computing system.