The deduction (phased in over 15 years) equals the lesser of either the taxpayer's book-tax difference for the stated fiscal period or the taxpayer's net deferred tax liability, as computed in accordance with GAAP. Therefore, both the book-tax calculation and the net deferred tax liability are necessary to compute the deduction to business income. Thus, when UBG members depart or arrive they must consider both the book-tax difference and the net deferred tax liability.

In the instance of a member leaving the group, the departing member will leave the group with its individually calculated book-tax number as reported on Form 4593 with the UBG's initial MBT return. Likewise, the departing member leaves the group with its share of the net deferred tax liability. If the group members calculated this amount individually then the departing member would simply leave the group with its individual amount. If the group calculated the net deferred tax liability only at the group level then the departing member must figure its pro rata share of the amount, computed as if the member had been a single entity filing a stand alone return when the liability was booked.