Late income tax return filing triggers loss carryforward disallowance, interest and penalties under income tax law. Late filing of an income tax return disqualifies carry forward of specified losses, bars certain Chapter VI-A deductions, and attracts penal interest for the period of delay. It may also invite a statutory penalty or fee for default under revised filing provisions and causes interest on refunds to run from the date of filing; willful non-filing can lead to prosecution.