tax calculations

[sharif lakhani]

My employer has given me tax deduction certificate and I cant calculate how they have calculated the tax. I mean there comes difference. If I calculate it give more tax amount but company has deducted less which means there are some items which are not taxable. please advise out of there which one is not tax able
basic salary
medical allowance
house rent
utilities allowance
conveyance allowance
dealing allowance
I have little hint that medical allowance is exempt? am I right? if so to what extent.
Thanks