(c) Partial year of participation.

1. (1) Under section 204(b)(3)(C) of the Act and section 411(b)(3)(C) of the Code, in calculating an employee's period of service for purposes of benefit accrual, a plan is not required to take into account a 12-consecutive-month period during which the employee's service is less than 1,000 hours of service. In measuring an employee's service for purposes of section 204(b)(3)(C) of the Act and section 411(b)(3)(C) of the Code, a plan shall use the accrual computation period designated under paragraph (a) of this section. Under section 204(b)(3)(B) of the Act and section 411(b)(3)(B) of the Code, in the case of an employee whose service is not less than 1,000 hours of service during an accrual computation period, the calculation of such employee's period of service will not be treated as made on a reasonable and consistent basis unless service during such computation period is taken into account. To the extent that the employee's service during the accrual computation period is less than the service required under the plan for a full year of participation, the employee must be credited with a partial year of participation equivalent to no less than a ratable portion of a full year of participation.
2. (2) For purposes of calculating the portion of a full year of participation to be credited to an employee whose service during a computation period is not less than 1,000 hours of service but is less than service required for a full year of participation in the plan, the plan may credit the employee with a greater portion of a full year of participation than a ratable portion, or may credit an employee with a full year of participation even though the employee's service is less than the service required for a full year of participation, provided that such crediting is reasonable and is consistent for all employees within the same job classifications, reasonably established.
3. (3) In the case of an employee who commences participation in a plan (or recommences participation in the plan upon the employee's return after one or more 1-year breaks in service) on a date other than the first day of an applicable accrual computation period, all hours of service required to be credited to the employee during the entire accrual computation period, including hours of service credited to the employee for the portion of the computation period before the date on which the employee commences (or recommences) participation, shall be taken into account in determining whether the employee has 1,000 or more hours of service for purposes of section 204(b)(3)(C) of the Act and section 411(b)3)(C) of the Code. If such employee's service is not less than 1,000 hours in such accrual computation period, the employee must be credited with a partial year of participation which is equivalent to no less than a ratable portion of a full year of participation for service credited to the employee for the portion of the computation period after the date of commencement (or recommencement) of participation.

4. (4) Examples. The following are examples of reasonable and consistent methods for crediting partial years of participation:

   1. (i) A plan requires 2,000 hours of service for a full year of participation. An employee who is credited during a computation period with no less than 1,000 hours of service but less than 2,000 hours of service is credited with a partial year of participation equal to a portion of a full year of participation determined by dividing the number of hours of service credited to the employee by 2,000.

   2. (ii) A plan requires 2,000 hours of service for a full year of participation. The plan credits service in an accrual computation period in accordance with the following table:

      Hours of service credited	Percentage of full year of participation credited
      1000	50
      1001 to 1200	60
      1201 to 1400	70
      1401 to 1600	80
      1601 to 1800	90
      1801 and above	100

      Under this method of crediting partial years of participation, each employee who is credited with not less than 1,000 hours of service is credited with at least a ratable portion of a full year of participation.

   3. (iii) A plan provides that each employee who is credited with at least 1,000 hours of service in an accrual computation period must receive credit for at least a partial year of participation for that computation period. For full accrual, however, the plan requires that an employee must be credited with a specified number of hours worked; employees who meet the 1,000 hours of service requirement but who are not credited with the specified number of hours worked required for a full year of participation are credited with a partial year of participation on a prorata basis. For example, if the plan requires 1,500 hours worked for full accrual, an employee with 1,500 hours worked would be credited with full accrual, but an employee with 1,000 hours worked and 500 other hours of service would be credited with 2/3 of full accrual. The plan's method of crediting service for accrual purposes is consistent with the requirements of this paragraph. It should be noted, however, that use of hours worked as a basis for prorating benefit accrual may result in discrimination prohibited under section 401(a)(4) of the Code.
   4. (iv) Employee A is employed on June 1, 1980 in service covered by a plan with a calendar year accrual computation period, and which requires 1,800 hours of service for a full accrual. Employee A completes 500 hours from June 1, 1980 to December 31, 1980, and completes 100 hours per month in each month during 1981. A is admitted to participation on July 1, 1981. A is credited with 1,200 hours of service for the accrual computation period beginning January 1, 1981. Under the rules set forth in paragraph (c)(3) of this section, A is required to be credited with not less than one-third of a full accrual (600 hours divided by 1,800 hours).

(d) Prohibited double proration.

1. (1) In the case of a defined benefit plan that (i) defines benefits on a basis which has the effect of prorating benefits to reflect less than full-time employment or less than maximum compensation and (ii) does not adjust less-than-full-time service to reflect the equivalent of full-time hours or compensation (as the case may be), the plan may not further prorate benefit accrual under section 204(b)(3)(B) of the Act and section 411(b)(3)(B) of the Code by crediting less than full years of participation, as would otherwise be permitted under paragraph (c) of this section. These plans must credit, except when service may be disregarded under section 204(b)(3)(C) of the Act and section 411(b)(3)(C) of the Code (relating to less than 1,000 hours of service), less-than-full-time employees with a full year of participation for the purpose of accrual of benefits.

2. (2) Examples.

   1. (i) A plan's defined benefit formula provides that the annual retirement benefit shall be 2 percent of the average compensation in all years of participation multiplied by the number of years of participation. Employee A is a full-time employee who has completed 2,000 hours during each of 20 accrual computation periods. A's average hourly rate was $5 an hour. Thus, A's average compensation for each year during participation in the plan is $10,000 ($5 per hour multiplied by 2,000 hours). If the plan states that a full year of participation is 2,000 hours, then A's annual retirement benefits, if he retired at that time, would be $4,000 ($10,000 per year of compensation × .02 × 20 years of participation). Employee B, however, is a part-time employee who completes 1,000 hours of service during each of 20 accrual computation periods. Like A, B's average hourly rate is $5 per hour. B's average compensation for his total years of participation is $5,000 ($5 per hour multiplied by 1,000 hours). Thus, the plan's benefit formula, by basing benefits on an employee's average compensation in all years of participation, in effect prorates benefits to reflect the fact that during B's participation in the plan, he has earned less than the maximum compensation that a full-time employee paid at the same rate could earn during the same period of participation in the plan. Under the rule of subparagraph (1), therefore, the plan is not permitted to prorate B's years of participation to reflect B's less than full-time employment throughout his participation in the plan. Therefore, B's annual retirement benefit would be $2,000 ($5,000 average compensation × .02 × 20 years of participation). (If double proration were permitted, then B's total years of participation would be only 10 since he would be credited with only one-half of a year of participation during each of the accrual computation periods (1,000/2,000). Thus, B's annual retirement benefit would be $1,000—i.e., $5,000 average compensation × .02 × 10 years of participation.)
   2. (ii) If the plan adjusts the average compensation during plan participation to reflect full compensation, then the plan may prorate years of participation. Thus, the average full annual compensation for B would be $10,000 rather than the $5,000 actually paid. Employee B's annual retirement benefit would then be $2,000 ($10,000 average full compensation × .02 × 10 years of participation).

(e) Amendments to change accrual computation periods.

1. (1) A plan may be amended to change the accrual computation period to a different 12-consecutive-month period, provided that the period between the end of the last accrual computation period under the plan as in effect before such amendment and the beginning of the first accrual computation period under the plan as amended is treated as a partial accrual computation period in accordance with the rules set forth in paragraph (e)(2) of this section.

2. (2) In the case of a partial accrual computation period, the following rules shall apply:

   1. (i) A plan having a minimum service requirement expressed in hours of service (or other units of service) for benefit accrual in a full accrual computation period (as permitted under section 204(b)(3)(B) of the Act and section 411(b)(3)(B) of the Code) may apply a minimum service requirement for benefit accrual in a partial accrual computation period which is equal to the plan's minimum service requirement for benefit accrual in a full accrual computation period, multiplied by the ratio of the length of the partial accrual computation period to a full year.
   2. (ii) In the case of a participant who meets a plan's minimum service requirement for benefit accrual in a partial accrual computation period (as permitted under paragraph (e)(2)(i) of this section), the plan shall credit the participant with at least a partial year of participation for purposes of benefit accrual. Credit for a partial accrual computation period shall be determined in accordance with paragraphs (c) and (d) of this section.
3. (3) Example. Effective October 1, 1977, a plan is amended to change the accrual computation period from the 12-consecutive-month period beginning on January 1 to the 12-consecutive-month period beginning on October 1. The period from January 1, 1977 to September 30, 1977 must be treated as a partial accrual computation period. The plan has a requirement that a participant must be credited with 1,000 hours of service in an accrual computation period in order to be credited with a year of participation for purposes of benefit accrual. For the partial accrual computation period the plan may require a participant to be credited with 750 hours of service in the partial accrual computation period in order to receive credit for purposes of benefit accrual (1,000 hours of service multiplied by the ratio of 9 months to 12 months). To the extent permitted under paragraph (d) of this section, the plan may prorate accrual credit on whatever basis the plan uses to prorate accrual credit for employees whose service is 1,000 hours of service or more but less than service required for full accrual in a full accrual computation period.