Return filing deadline: monthly GSTR-3B returns due by the twentieth day after the month; payments via electronic ledgers. Returns in FORM GSTR-3B for October 2019 to March 2020 must be filed electronically through the common portal on or before the twentieth day of the month following the taxable month; registered persons must discharge tax, interest, penalty, fees or other amounts by debiting the electronic cash ledger or electronic credit ledger, as applicable, no later than that same due date.