29 CFR § 780.306 - Calendar quarter of the preceding calendar year defined.
In applying section 13(a)(6)(A), it is necessary to consider each of the four calendar quarters (January 1–March 31; April 1–June 30; July 1–September 30; October 1–December 31) in the preceding calendar year (January 1–December 31). If in any calendar quarter of the preceding calendar year the employer used more than 500 man-days of agricultural labor, he must comply with the minimum wage requirements of section 6(a)(5) with respect to any employee not otherwise exempt in the current year. Compliance with the Act is required in the current year regardless of the number of man-days of agricultural labor used in the current year. On the other hand, if in the preceding calendar year the number of man-days used did not exceed 500 in any calendar quarter, there is no requirement to comply with respect to employment of agricultural labor in the current calendar year regardless of how many man-days are used in any calendar quarter of the current calendar year. Such employees are exempt under the basic provisions of section 13(a)(6)(A).