The due date of filing GSTR 1 for the period from July 2017 to September 2018 was extended till 31st October 2018 vide Notification No. 43/2018, CT dated 10-09-2018 ( for taxpayers having aggregate turnover upto Rs. 1.5 Crore ) and Notification No. 44/2018, CT dated 10-09-2018 ( for taxpayers having Aggregate Turnover more than Rs.1.5 crore ).
You just have to calculate LATE FEES from 1st November 2018 onwards as mentioned below :
For NIL Return : Rs.20 per day ( Rs. 10 per Act )
For Tax Liability Return : Rs. 50 per day ( Rs. 25 per Act ).