(a) If a portion of the services performed by an employee for an employer during a pay period constitutes employment, and the remainder does not constitute employment, all the services performed by the employee for the employer during the period shall for purposes of the taxes be treated alike, that is, either all as included or all as excluded. The time during which the employee performs services which under section 3121(b) constitute employment, and the time during which he performs services which under such section do not constitute employment, within the pay period, determine whether all the services during the pay period shall be deemed to be included or excluded.

(b) If one-half or more of the employee's time in the employ of a particular person in a pay period is spent in performing services which constitute employment, then all the services of that employee for that person in that pay period shall be deemed to be employment.

(c) If less than one-half of the employee's time in the employ of a particular person in a pay period is spent in performing services which constitute employment, then none of the services of that employee for that person in that pay period shall be deemed to be employment.

(d) The application of the provisions of paragraphs (a), (b), and (c) of this section may be illustrated by the following example:

(e) For purposes of this section, a “pay period” is the period (of not more than 31 consecutive calendar days) for which a payment of remuneration is ordinarily made to the employee by the employer. Thus, if the periods for which payments of remuneration are made to the employee by the employer are of uniform duration, each such period constitutes a “pay period”. If, however, the periods occasionally vary in duration, the “pay period” is the period for which a payment of remuneration is ordinarily made to the employee by the employer, even though that period does not coincide with the actual period for which a particular payment of remuneration is made. For example, if an employer ordinarily pays a particular employee for each calendar week at the end of the week, but the employee receives a payment in the middle of the week for the portion of the week already elapsed and receives the remainder at the end of the week, the “pay period” is still the calendar week; or if, instead, that employee is sent on a trip by such employer and receives at the end of the third week a single remuneration payment for three weeks' services, the “pay period” is still the calendar week.

(f) If there is only one period (and such period does not exceed 31 consecutive calendar days) for which a payment of remuneration is made to the employee by the employer, such period is deemed to be a “pay period” for purposes of this section.

(g) The rules set forth in this section do not apply (1) with respect to any services performed by the employee for the employer if the periods for which such employer makes payments of remuneration to the employee vary to the extent that there is no period “for which a payment of remuneration is ordinarily made to the employee”, or (2) with respect to any services performed by the employee for the employer if the period for which a payment of remuneration is ordinarily made to the employee by such employer exceeds 31 consecutive calendar days, or (3) with respect to any service performed by the employee for the employer during a pay period if any of such service is excepted by section 3121(b)(9) (see §31.3121(b)(9)-1).

(h) If during any period for which a person makes a payment of remuneration to an employee only a portion of the employee's services constitutes employment, but the rules prescribed in this section are not applicable, the taxes attach with respect to such services as constitute employment as defined in section 3121(b).

[T.D. 6516, 25 FR 13032, Dec. 20, 1960, as amended by T.D. 6744, 29 FR 8313, July 2, 1964]