Closing stock is the balance of unsold goods that are remaining from the purchases made during an accounting period. The value of total purchases is already included in the Trial Balance . If closing stock is included in the Trial Balance , the effect will be doubled. Hence, it will not reflect in the Trial Balance.

Suppose total purchases during an accounting period inside a Trial Balance are: 10,000 

Closing Stock: 2,000 (This is included in purchases already)

 If both of these figures are shown in trial balance then there will be a mismatch of 2,000 because the effect has now been doubled in the trial balance. 

 Also, No separate account is opened for closing stock inside the general ledger. Hence, closing stock is not to be shown in the trial balance.