Return filing deadlines for GSTR-3B set: most taxpayers file by twentieth; small taxpayers by twenty fourth. Filing deadlines for GSTR-3B returns for October to March are electronic through the common portal by the twentieth day succeeding each month, with a concessionary deadline of the twenty fourth day for taxpayers below the small turnover threshold. Tax liabilities must be discharged by debiting the electronic cash ledger or electronic credit ledger as applicable, while interest, penalty, fees and other amounts must be debited from the electronic cash ledger, completed no later than the return's due date.