There is no 70% or 80% base for contribution of PF, but PF should be contributed on 100% of the salary. Here, salary means the amount of remuneration agreed with the employee in return for the services/labour that he puts. Obviously, any incentive that is earned as a result of satisfying certain conditions, like achieving certain sales/production figures, goals, etc., or overtime wages, which are also amounts earned on satisfying a condition of working beyond a certain fixed period per day or week, are outside the purview of wages for paying PF.
Though the EPF & MP Act excludes HRA from wages, the same applies only to such allowances that are paid to those who reside in rented houses as part of their employment.
You may have different components in your salary, like Basic, Dearness allowance, HRA, Special allowance, traveling allowance, etc. A very simple test to decide which of these components of salary will qualify for PF contribution is to see on which component you will deduct Loss Of Pay if an employee remains absent without pay. Certainly, it is not the basic alone or Basic and DA alone that are not paid when an employee is on leave without pay, but the entire component is not paid. As such, the total salary is the salary that qualifies for PF contribution. HRA, if paid separately to those who stay in rented houses, will obviously be paid in full even if he is on leave. Therefore, only such HRA will be excluded from the salary.
If the total salary exceeds Rs 15000, naturally, the employer can restrict the PF qualifying salary to Rs 15000.