(a) General rule. Under this section, the amount of unfunded vested benefits allocable to an employer that withdraws from a merged plan after the initial plan year is the sum of the employer's proportional share, if any, of the unamortized amount of the plan's initial plan year unfunded vested benefits (determined under paragraph (b) of this section) and the employer's proportional share of the unamortized amount of the unfunded vested benefits arising after the initial plan year (determined under paragraph (c) of this section).

(b) Share of initial plan year unfunded vested benefits. An employer's proportional share, if any, of the unamortized amount of the plan's initial plan year unfunded vested benefits is the sum of the employer's share of its prior plan's liabilities, as determined under § 4211.32(b)(1), and the employer's share of the adjusted initial plan year unfunded vested benefits, as determined under § 4211.32(b)(2), with such sum reduced as if it were being fully amortized in level annual installments over five years beginning with the first plan year after the initial plan year.

(c) Share of unfunded vested benefits arising after the initial plan year. An employer's proportional share of the amount of the plan's unfunded vested benefits arising after the initial plan year is the employer's proportional share determined under § 4211.33(c).