29 CFR § 779.265 - Basis for making computations.
The annual gross dollar volume of sales made or business done of an enterprise or establishment consists of the gross receipts from all of its sales or its volume of business done during a 12-month period. Where a computation of the annual gross volume is necessary to determine monetary obligations to employees under the Act whether in an enterprise which has one or more retail or service establishments, or in any establishment in such enterprise, or in any gasoline service establishment, it must be based on the most recent prior experience which it is practicable to use. This was recognized in the Congress when the legislation was under consideration. (S. Rept. No. 145, 87th Cong., first session, p. 38 discusses in detail the calculation of the annual gross volume.) When gross receipts of an enterprise show that the annual dollar volume of sales made or business done meets the statutory tests for coverage and nonexemption, the employer must comply with the Act's monetary provisions from that time on or until such time as the tests are not met. (See § 779.266.)