The income of a entity may not match with the Total income that is arrived at as per Income Tax Act, 1961. Probable reasons for the difference are, depreciation method followed in the books, certain expenses not allowable under IT Act U/s.40(a), 43B etc., However, certain expenses which are disallowed in one year can be availed in the subsequent year on complying with law (like payments on which TDS subsequently remitted, statutory dues subsequently paid and even the depreciation which in the due course vary). These differences which are capable of reversal in the subsequent years are called 'timing differences'.
Provision for Income-tax that is provided in the books is as per IT Act. However, the tax benefit/reversal that is known to the entity as on the date of Balance Sheet and which is capable of accruing in the subsequent years is to be reflected in the books so as to give a true and fair view.
Hence, rate equal to tax on the timing differences is provided in the books as per AS-22.