Yes, if you have not furnished the return within the due date, you will have to pay interest on tax due.
If the return is not filed up to the end of the assessment year, in addition to interest, a penalty of Rs. 5,000 shall be levied under section 271F . [No penalty section 271F would be levied w.e.f. Assessment Year 2018-19]
Note: W.e.f. assessment year 2018-19, fee as per section 234F is required to be paid if return is furnished after due date. Fee for default in furnishing return of income will be as follows:
i Rs. 5000 if return is furnished on or before the 31st day of December of the assessment year;
ii Rs. 10,000 in any other case
However, late filing fee shall not exceed Rs. 1000 if the total income of an assessee does not exceed Rs. 5 lakh.