29 C.F.R. § 4211.4 — Contributions for purposes of the numerator and denominator of the allocation fractions.

(a) In general. Subject to paragraph (b) of this section, each of the allocation fractions used in the presumptive, modified presumptive and rolling-5 methods is based on contributions that certain employers have made to the plan for a 5-year period.

(1) The numerator of the allocation fraction, with respect to a withdrawing employer, is based on the “sum of the contributions required to be made” or the “total amount required to be contributed” by the employer for the specified period.

(2) The denominator of the allocation fraction is based on contributions that certain employers have made to the plan for a specified period.

(b) Disregarding surcharges and contribution increases. For each of the allocation fractions used in the presumptive, modified presumptive and rolling-5 methods in determining the allocation of unfunded vested benefits to an employer, a plan in endangered or critical status must disregard:

(1) Surcharge. Any surcharge under section 305(e)(7) of ERISA and section 432(e)(7) of the Code.

(2) Contribution increase. Any increase in the contribution rate or other increase in contribution requirements that goes into effect during plan years beginning after December 31, 2014, so that a plan may meet the requirements of a funding improvement plan under section 305(c) of ERISA and section 432(c) of the Code or a rehabilitation plan under section 305(e) of ERISA and 432(e) of the Code, except to the extent that one of the following exceptions applies pursuant to section 305(g)(3) or (4) of ERISA and section 432(g)(3) or (4) of the Code:

(i) The increases in contribution requirements are due to increased levels of work, employment, or periods for which compensation is provided.

(ii) The additional contributions are used to provide an increase in benefits, including an increase in future benefit accruals, permitted by section 305(d)(1)(B) or (f)(1)(B) of ERISA and section 432(d)(1)(B) or (f)(1)(B) of the Code.

(iii) The withdrawal occurs on or after the expiration date of the employer's collective bargaining agreement in effect in the plan year the plan is no longer in endangered or critical status, or, if earlier, the date as of which the employer renegotiates a contribution rate effective after the plan year the plan is no longer in endangered or critical status.