A billing group is a set of accounts within your consolidated billing family – in the pro forma billing domain only – that share a common end customer. That end customer maintains the “Primary Account” and can see the cost and usage that accrues across its group. Each billing group’s pro forma usage is computed as its own consolidated billing family, sharing RI and Savings Plans benefits only within the group and accrues volume tier discounts (e.g., S3 and CloudFront) and an “always” free tier offering. An account can only belong to one billing group during a billing period.