Why is my deposit interest income lower than the interest rate?

If the interest income for a deposit exceeds Rs. 10,00 in a year(from all bank branches) the bank is needed to deduct a TDS on the amount.  A 10% TDS is deducted if PAN details are available and 20% if PAN details are not available. 

If your total income is below the taxable limit, you can avoid tax deduction on these deposits by submitting Form 15G and Form 15H to the bank requesting them not to deduct any TDS. This should ideally be done at the start of the Financial Year to avoid any deductions. 

Form 15H is for senior citizens(those who are 60 years or older) and Form 15G is for everybody else. Alternatively, you can file your income tax return and claim the refund.