P2:Share-based payment的递延税影响

书上说暂时性差异计算如下：

Carrying amount of share-based payment expense                                0
Less tax base of share-based paymeng expense
(extimated amount tax authorities will permit as a deduction)                 (X)
=Temporary difference                                                                          
   Deffered tax asset at X%

不是很明白carrying amount of share-based payment expense
怎么会是0，明明当年会计上是会确认share-based payment expense的啊，麻烦大家指教~~谢谢~~