Return due date for GSTR: monthly GSTR-3B returns must be filed by the twentieth day of the succeeding month. Returns in FORM GSTR-3B for October 2019 to March 2020 must be furnished electronically through the common portal on or before the twentieth day of the month succeeding each month. Registered persons shall discharge tax, interest, penalty, fees or other payable amounts by debiting the electronic cash ledger or electronic credit ledger, as applicable, not later than that filing due date, subject to statutory payment provisions. The notification is effective from 9th October, 2019.