GSTR-3B filing due date and tax payment timing fixed for July to September 2019 returns under GST The return in FORM GSTR-3B for July 2019 to September 2019 must be furnished electronically through the common portal on or before the twentieth day of the succeeding month. Every registered person furnishing the return must, subject to section 49, discharge liability towards tax, interest, penalty, fees or any other amount payable under the Act by debiting the electronic cash ledger or electronic credit ledger by that same prescribed date.