New Plan - Prior Service

[HafnerN1]

I have a start-up 401(k) plan excluding all prior service (effective 1/1/17).  Eligibility is 21/1, calendar year plan.  If an employee was hired 10/1/2016 will their eligibility computation period be 10/1/16 - 9/30/17 due to it being their first year of employment?  Or since the plan excludes prior service is the eligibility comp period 1/1/17 - 12/31/17?  Thanks!

[WCC]

From the EOB:   All service with the employer must be credited, even service before the plan is established, unless disregarded under the break in service rules

See  IRC §410(a)(5)(A)

service for eligibility purposes cannot be excluded unless under the above referenced break in service rules

[Belgarath]

Sometimes people get this confused with crediting prior service for VESTING purposes. Perfectly ok to exclude service prior to establishment of the plan for VESTING. Not for eligibility, as WCC mentions. You might want to check your document 'cause I suspect that the exclusion for prior service may be for vesting.