Hi Prasanna,
In my knowledge there is no specific rule to basic percent. You can put 100% gross as Basic. But, It will increase Taxes on employees part, CTC on employer part.
You have to decide % of basic on gross keeping few points in mind.
1. According to India Law Basic + Da will be consider as salary/wage (on BASIC + DA you have to pay Bonus, Gratuity, EPF etc) before finalize read these acts and its applicability and your liability.
2. Allowances you have to go through Income tax act. Try to reduce Income tax on hand of employee. More take home will help you to retain your employees for longer time. (Like travel allowance Rs. 800, HRA 40% OR 50% OF BASIC, Leave travel, Medical Expenses, Food Pass etc.)
