Penalty calculation

From due date to till the date of filing.
25/- +25/- (CGST +Sgst) per day & for Nil return it's 20/-+20/- per day

But portal autocalculate the late filing of return

Fer nil return it is 10 + 10

The Late Fees levied u/s 47 of the CGST Act 2017 is auto calculated by the portal itself while filing GSTR-3B.

The Late Fees of GSTR-3B is :

Liability Return : Rs. 25 per day per Act [ Rs. 25 under CGST + Rs. 25 under SGST ].

NIL Return : Rs. 10 per day per Act [ Rs. 10 under CGST + Rs. 10 under SGST = Total Rs. 20 per day ].

and in referance to above it can not be more than 10000 means 5000 for CGST and 5000 for SGST

Sorry yes it's 10+10 for Nil return

For Nil Return the Late Fees is Rs. 20 per day ( 10+10 )