Interest accrues on tax due when you have not paid taxes at all, or in full or the TDS deducted by the employer wasn’t enough.
Interest is levied when 90% of the income tax is not paid by the end of March. Interest is also charged when you file income tax returns after the due date. These are covered under Section 234A, 234B, 234C.
You can read more about it here: http://blog.cleartax.in/when-is-interest-payable-on-taxes/