GSTR-3B filing deadline: returns due monthly on the twentieth day following each month; payments from electronic ledgers. Registered persons must furnish FORM GSTR-3B electronically through the common portal on or before the twentieth day of the month succeeding each tax month, and must discharge tax, interest, penalty, fees or other amounts payable by debiting the electronic cash ledger or electronic credit ledger, as applicable, not later than that last date.