Dear Seja,
It will not vary.
PF will be deducted 12%(or Rs.780/- in some organisation where basic pay is more than 6,500) from employees
ESI will be deducted 1.75% from employees(upto Gross salary Rs.15,000)
The following are the case where the PF & ESI contribution varies.
PF will vary only in the month when an employee work on the National festival holiday or if he is absent.
Eg. If employee is paid for 31 days in january, If he works on 1st, 26th then he has to be paid double wages for the 2 days. here the basic salary will vary because he will be paid for 33 days.
Similarly if an employee is absent for 2 days then he will get the salary for 29 day( Here also basic pay varies
ESI will vary only if the employee is paid overtime, monthly incentive or attendance bonus or National festival holiday.( Here even the gross amount increases more than 15000 the ESI amount will be deducted for the actual gross earned)