Income tax expenses in p&l

when we are filing the return of a company at the end of every FY will make a provision for the income tax to be paid..
at the begining that entry will be reversed...
so now my question is will make the provision by adding back all our income tax expenses and all in order to get net profit before the p&l...
so how to calculate current tax which will arise in profit and loss a/c of the company in order to get net profit before tax profit and loss ..