Due date of gstr1 for March month

It will be last week of June 2020.

For Turnover less than 5 Crore Last Week of June 20 and For More Than 5 Crore for March 20 is 05.05.20

The Finance Ministry on Tuesday announced the extension of the deadline for filing returns of goods and services tax (GST) for March, April and May 2020 till June.

Companies with turnover of above Rs 5 crore will not have to pay any late fee or penalty but will have to file a 9 per cent interest rate for late filing of GST.
whose turnover is less than 5 croore in no interest and penalty.

** For 3B and for GSTR 1 Last Week of June 2020

As per press release on 14/3/2020, time limit for any compliances under GST law where the limit is expiring between 20th march to 29th June 2020 shall be extended to 30/6/2020

The due date for filing FORM GSTR-1 for the month of March, April and May 2020 has been extended to "30.06.2020" and all the applicable Late Fees ( levied u/s 47 of the CGST Act 2017 ) has been waived off, as per Notification No. 33/2020 - Central Tax, dated 03.04.2020.