Explanation
GSTR-3B is filed under CGST Act Section 39 (read with Rule 61). It is a summary return — not invoice-level. Monthly filers (AATO > ₹5 crore or opted out of QRMP) file by the 20th. QRMP filers (AATO ≤ ₹5 crore) file a quarterly 3B by the 22nd (southern/western states) or 24th (northern/eastern states). Late fee: ₹50/day (₹25 CGST + ₹25 SGST) for returns with tax liability; ₹20/day (₹10+₹10) for nil returns. Interest at 18% per annum on delayed tax payment (Section 50 CGST Act). Cannot file a 3B more than 3 years past due date. Verify on the GST portal before filing.