GSTR-1 vs GSTR-3B: how to reconcile the two returns

What each return does

GSTR-1 and GSTR-3B are often filed in the same week and treated as the same job. They are not. Section 37 is the outward-supply statement. Section 39 is the return through which tax is paid. One feeds your customer's GSTR-2B. The other settles your liability.

Filing GSTR-3B on time with a short GSTR-1, or a complete GSTR-1 with a short GSTR-3B, are different errors. The portal now polices the second one automatically.

Why the two returns diverge

A gap is not always a missed payment. It is often a classification or a timing difference that the portal cannot see.

• Invoices reported in GSTR-1 and then amended, while GSTR-3B was filed on the original figure.
• Credit notes or debit notes in GSTR-1 that were never taken through Table 3.1 of GSTR-3B.
• Advances, reverse charge or deemed supplies treated in one return and ignored in the other.
• QRMP IFF invoices that were also typed into the quarterly GSTR-1, so outward tax is counted twice against a single 3B.
• A rounding or place-of-supply split that changes IGST versus CGST/SGST without changing the total, which still looks like a table-level mismatch.

The dangerous gap is the simple one: GSTR-1 went out with the full invoice book, and GSTR-3B was filed on an older MIS. That is the gap rule 88C was written to catch.

A working reconciliation

Keep this to a single worksheet per tax period. If the worksheet needs more than these rows, the books are not ready to file.

1. Pull outward taxable value and tax from the GSTR-1 / IFF that will be (or has been) filed, including amendments and notes.
2. Pull Table 3.1 of GSTR-3B for the same period, tax-head wise.
3. Split the difference into invoice missing in 3B, note missing in 3B, advance or reverse-charge item, and unexplained.
4. File GSTR-3B only after the unexplained line is zero, or after you have a written reason that will survive a DRC-01B reply.

Do the same pass in reverse after 3B is filed, because a later GSTR-1 amendment can reopen the gap. That is how a period you thought was closed produces an intimation the following month.

When DRC-01B arrives

Rule 88C tells the portal to compare outward tax in GSTR-1, as amended in GSTR-1A if any, or in the IFF, with tax paid in GSTR-3B for the same period. If GSTR-1 is higher by the amount and the percentage the Council has recommended, you get Part A of Form GST DRC-01B.

The official GST tutorial is specific about what follows:

• You are told by email and SMS, with a reference number. The same intimation sits at Services → Returns → Return Compliance → Liability Mismatch DRC-01B.
• Regular taxpayers, SEZ units and developers, casual taxpayers, and people who have opted into or out of composition can all receive it.
• Monthly filers can get it after each monthly GSTR-3B. QRMP filers get it, if it applies, after the quarterly GSTR-3B.
• If Part B is not filed, GSTR-1 or IFF for the next period will not go through.

The threshold itself is a portal configuration, not a number you should copy from a blog. Read the Part A you actually received.

How to reply without blocking the next GSTR-1

Part B is the reply. You either pay the difference or explain it. The official filing manual is the sequence to follow, not a consultant's screenshot.

1. Open the intimation from Return Compliance → Liability Mismatch DRC-01B and read the period and the tax-head difference.
2. If the tax is actually payable, file Form GST DRC-03 for that difference. The cause of payment must be "Liability mismatch - GSTR-1 to GSTR-3B". The DRC-03 must be dated on or after Part A, must be for the same GSTIN, and must cover the same period (the month for monthly filers, or at least one month inside the quarter for QRMP).
3. If the tax is not payable, pick the reason the form offers and attach the explanation. Delete a reason's details before you deselect it, or the portal will reject the save.
4. Submit Part B. The official FAQ says GSTR-1 or IFF can be filed immediately afterwards. If it stays locked, log out and log back in.

A DRC-03 filed for the wrong cause, the wrong period, or a date before Part A will not unlock the next GSTR-1. That is the error the official FAQ already names.

How to verify on official sources

1. Confirm the legal split in section 37 and section 39 of the CGST Act, or on India Code.
2. Read the DRC-01B FAQs and the filing manual on the official GST tutorial before you reply to an intimation.
3. Check live system notices on the GST portal and any related circular on CBIC GST.

Due dates for the two returns live on the GST return due date page. This page is only the reconciliation. Do not treat a due-date extension as a licence to leave the two returns unreconciled.

Where Complied AI fits

The comparison itself is in the Act. What moves is the circular or portal notice that changes a threshold, a form, or a lock. CBIC / GST updates on Complied AI keep those notices in one feed so you can open the source document and then read section 37 or section 39 next to it.