Meaning of ALLOWABLE in English

al ‧ low ‧ a ‧ ble /əˈlaʊəb ə l/ BrE AmE adjective

1 . acceptable according to the rules SYN permissible :

The maximum allowable dosage is two tablets a day.

2 . allowable costs are costs that you do not pay tax on:

allowable deductions such as alimony and business expenses

Longman Dictionary of Contemporary English.      Longman - Словарь современного английского языка.