Dear
"If gross is X, how much proportion should be taken as Basic pay?" type of question has been flooding this forum. Please search CiteHR for answer to your query.
To go to the root of the problem, such situation is arising because HR these days, esp. in 'baniya/lalaji" companies, fix the Gross salary first.
Actually, it is (and should be) the other way round. Basic pay (by its very nature, indicated by its name) should be fixed first; since all other calculations including perks emanate from it, one just need to total the various components to arrive at the Gross salary.
However, the practice prevailing, initiated by half-baked HRs, is to arrive at the Gross Salary first and then to work backwards to "guess-estimate" the Basic Pay. A despisable, despicable, non-standard, ad-hoc, un-professional, arbitrary way of dealing with compensation issues.
It is a sure-shot indicator of the type of company it is.
Good companies seldom indulge in such practices.
Warm regards.