Abstract: A system determines a tiered charging rule with at least one step. Each step defines a quantity entry point and exit point for the step and defines an alteration rule to be applied to charges falling within the step. The system determines a quantity usage range based on usage related to a billing event. The system range intersects each step range with the quantity usage range to determine applicable steps for the quantity usage range. For each applicable step, the system calculates a step charge based on the length of the applicable step range and a base per unit charge rate and applies an alteration to the step charge based on the corresponding alteration rule for the step.