GSTR-3B is the monthly (or QRMP quarterly) self-assessed summary return every regular GST registrant files, declaring outward supplies, input tax credit claimed, and net tax payable for the period.
What each section covers
Table 3.1 — Outward and inward supplies liable to reverse charge. This is where total taxable turnover for the period is declared, split by supply type (taxable, zero-rated, nil-rated/exempt, and inward supplies under reverse charge).
Table 3.2 — Inter-state supplies to unregistered persons, composition dealers and UIN holders. A further breakdown of specific inter-state supplies already included in 3.1.
Table 4 — Eligible ITC. Input tax credit is declared here in three stages: ITC available (from GSTR-2B), ITC reversed (for specific reasons under Rules 42/43 or ineligible credit under Section 17(5)), and net ITC available for utilisation.
Table 5 — Exempt, nil and non-GST inward supplies. Reported for information; doesn't affect the tax computation directly, but mismatches here are a common point of departmental query.
Table 6.1 — Payment of tax. Tax payable is set off against available ITC first, then any balance is paid in cash through the electronic cash ledger.
The reconciliation step worth doing every month
The credit claimed in Table 4 should be reconciled against GSTR-2B — the auto-populated statement of eligible credit based on suppliers' filings — before the return is submitted, not after. Filing first and reconciling later means any mismatch is only caught at the annual return stage (GSTR-9/9C), by which point correcting it is considerably more work. A monthly working paper that ties the purchase register to GSTR-2B, line by line, catches supplier timing differences and genuine errors while they're still easy to fix.
Due date
GSTR-3B is due on the 20th of the following month for monthly filers, and per the QRMP scheme's staggered dates for quarterly filers who've opted in.
This is general information about the GSTR-3B filing process under the CGST Act and applicable rules, current as of the publish date above. It isn't a substitute for advice on your specific filing position.