Interest in late filing of GSTR 3B.

24% from the actual due date of March 20 3b return

18% interest rate

As per section 50 gst act interest rate 18 % on liability

50. Interest on delayed payment of tax.

[1] Every person who is liable to pay tax in accordance with the provisions of this Act or the rules made thereunder, but fails to pay the tax or any part thereof to the Government within the period prescribed, shall for the period for which the tax or any part thereof remains unpaid, pay, on his own, interest at such rate, not exceeding eighteen per cent., as may be notified by the Government on the recommendations of the Council.

[2] The interest under sub-section [1] shall be calculated, in such manner as may be prescribed, from the day succeeding the day on which such tax was due to be paid.