29 CFR 790.6 : Labor (§ 0.735-1 To Parts 4908-4999) — (§ 500.0 To Parts 871-899) — Regulations Relating To Labor (Continued) (§ 500.0 To Parts 871-899) — Wage And Hour Division, Department Of Labor (§ 500.0 To Parts 871-899) — Statements Of General Policy Or Interpretation Not Directly Related To Regulations (§ 775.0 To § 794.144) — General Statement As To The Effect Of The Portal-To-Portal Act Of 1947 On The Fair Labor Standards Act Of 1938 (§ 790.1 To § 790.22) — Provisions Relating To Certain Activities Engaged In By Employees On Or After May 14, 1947 (§ 790.3 To § 790.12) — Periods within the “workday” unaffected.

(a) Section 4 of the Portal Act does not affect the computation of hours worked within the “workday” proper, roughly described as the period “from whistle to whistle,” and its provisions have nothing to do with the compensability under the Fair Labor Standards Act of any activities engaged in by an employee during that period.

(b) “Workday” as used in the Portal Act means, in general, the period between the commencement and completion on the same workday of an employee's principal activity or activities. It includes all time within that period whether or not the employee engages in work throughout all of that period. For example, a rest period or a lunch period is part of the “workday”, and section 4 of the Portal Act therefore plays no part in determining whether such a period, under the particular circumstances presented, is or is not compensable, or whether it should be included in the computation of hours worked.