GSTR-1 vs GSTR-3B Mismatch in 2026 , A Reconciliation Reference

#gst #india #finance #compliance

If you build anything touching India's GST filings, the GSTR-1 vs GSTR-3B mismatch is what generates most automated notices. Here is a structured reference.

The filings
GSTR-1
Outward supplies. Every invoice issued, filed by the 11th of next month.
GSTR-3B
Tax summary and payment, filed by 20th/22nd/24th of next month.
They should agree. Most mismatches are timing: invoice in GSTR-1 for August, taxed in September's GSTR-3B because it was future-dated.

Three mismatches the portal auto-detects (2026)
Mismatch 1 , GSTR-1 liability > GSTR-3B payment:

Notice: DRC-01B (Rule 88C). Deadline: 7 days. Response: pay via DRC-03 or explain in Part B. No response = next GSTR-1 blocked.

Mismatch 2 , GSTR-3B ITC > GSTR-2B ITC:

Notice: DRC-01C (Rule 88D). Deadline: 7 days. Response: reverse excess ITC via DRC-03 or explain in Part B. No response = GSTR-1/IFF blocked.

Mismatch 3 , E-way bill vs GSTR-1:

Trigger: Movement without invoices pattern. Notice: ASMT-10 (30 days to reply via ASMT-11).

Zero Mismatch Policy (April 1, 2026)
Portal flags all differences immediately on filing. No grace thresholds for large taxpayers. The moment GSTR-1 and GSTR-3B diverge beyond zero, the flag fires.

Reconciliation sequence
Books → GSTR-1 → GSTR-3B Table 3.1(a) → GSTR-2B → E-invoice → E-way bill

Invoice Management System (IMS) , mandatory 2026
IMS shows supplier invoices as uploaded. Accept, reject, or pend each. Only accepted invoices flow into GSTR-2B for ITC. Supplier uploads an invoice on the 10th but you don't action it before the cut-off? ITC deferred to next month's GSTR-2B.

Building alerts for GST integrations
DRC-01B/C notices appear on the GST portal after each return filing date (11th, 20th, 22nd, 24th). 7-day response deadline. Build alerts for Day 1 and Day 5. Filing blockage on Day 8 is a serious compliance event.

Full reconciliation guide: taxgarden.in/blog/gstr-1-vs-gstr-3b-mismatch-reconciliation-guide-2026