GSTR-3B is a monthly (or quarterly under QRMP) summary return. Unlike the invoice-level GSTR-1, it reports consolidated figures: total outward supplies, input tax credit claimed, and the net GST payable, which is paid at the time of filing.
The output liability in GSTR-3B should reconcile with GSTR-1, and the ITC claimed should reconcile with GSTR-2B — mismatches are a common trigger for notices.
The form is short but every row is load-bearing. Outward taxable supplies and inward supplies liable to reverse charge make up the liability block; the ITC table sets out credit available, credit reversed and the net claimed; and the payment section discharges the result using credit first — in the permitted order — and cash for the balance, including all reverse-charge amounts. Exempt and nil-rated inward supplies are disclosed too, though they carry no tax.
The return now arrives largely pre-filled: liability flows in from GSTR-1 and credit from GSTR-2B, and the direction of travel is towards locking those figures rather than leaving them editable. The arithmetic stays simple — output tax of ₹54,000 against eligible credit of ₹36,000 means ₹18,000 in cash — but the judgement sits in the ITC table: what to claim, what to reverse, and what to defer until a supplier files.
Late payment attracts interest at the notified rate on the tax paid late, and late filing adds a fixed late fee per day, both computed by the portal. The habitual errors are quieter: skipping the reverse-charge rows entirely, reporting figures net that the form wants gross, claiming credit in the wrong row of the ITC table, and treating pre-filled numbers as authoritative without checking them against the books — the declaration is the taxpayer's, however it was populated.