GSTR-1 vs GSTR-3B: What Each Actually Reports (and Why They Must Match)

These are the two returns nearly every GST-registered business files, and they answer different questions about the same sales.

GSTR-1: the invoice-level detail

GSTR-1 reports every outward supply you made, invoice by invoice — who you sold to, the invoice number, the taxable value, the GST charged. This is what actually feeds your customers' input tax credit — the credit they claim is matched against what your GSTR-1 says you sold them, not what they say they bought. Due monthly by the 11th for regular filers, or quarterly under the QRMP scheme.

GSTR-3B: the summary and the payment

GSTR-3B is a self-assessed summary return — total outward supplies, total input tax credit claimed, and the net tax actually paid. It's due monthly by the 20th (QRMP filers pay via PMT-06 and file GSTR-3B quarterly, generally by the 22nd or 24th depending on state grouping). This is the return that actually moves money.

Why they need to match

GSTR-1 and GSTR-3B describe the same sales from two different angles — one detailed, one summarised — and the tax department reconciles them. A mismatch (GSTR-1 showing more sales than GSTR-3B reports tax on, or the reverse) is one of the most common triggers for a GST notice, because it looks like either under-reporting or a filing error either way.

What actually causes a mismatch

• An invoice entered in one return but forgotten in the other.
• A credit note issued after GSTR-1 was filed but not reflected before GSTR-3B.
• RCM liability calculated in GSTR-3B without a corresponding GSTR-1 entry — expected, since RCM purchases aren't your own outward supply, but worth understanding rather than assuming it's an error.
• Rounding or manual re-entry differences between two systems tracking the same numbers separately.

The reliable fix is structural, not vigilance: generate both from the same underlying invoice data instead of maintaining GSTR-1 and GSTR-3B as two separately-typed spreadsheets. See what a party ledger tracks for the same principle applied to customer balances instead of tax returns.