Form GSTR-3B filing deadline: returns and ledger-based payment must be completed by the twentieth day following each month. Returns in FORM GSTR-3B for April-June 2019 must be furnished electronically through the common portal on or before the twentieth day of the succeeding month, and all liabilities declared in that return must be discharged by debiting the electronic cash ledger or electronic credit ledger, as applicable, not later than that due date, subject to statutory payment provisions.