Content authored by practitioners with experience at Amazon India, Intuit QuickBooks, and the Tata Group. Meet the team →
GSTR-1 invoice-level output tax declarations and GSTR-3B summary tax payments frequently diverge because of period-end timing, late amendments via Tables 9A/9B/9C, and estimated 3B filings. Persistent variance triggers ASMT-10 scrutiny, DRC-01 demand notices, and 18% interest under Section 50.
Matching aligns every B2B, B2C, credit note, and amendment row from GSTR-1 against the output tax reported in GSTR-3B Tables 3.1 and 3.2 for the same period. Matching keys are GSTIN plus invoice number plus tax period plus tax head (IGST/CGST/SGST). Variance is classified into short-payment, excess-payment, amendment-lag, and period-shift so each one is remediated through the correct GSTR-1 Table 9 amendment or 3B Table 4 adjustment.
Configurable tolerance bands per tax head (zero for CGST/SGST, ₹1 for rounding), cut-off aligned to the 11th-20th filing window, and variance routing that surfaces short-payment cases before the 20th to avoid interest.
Reconciled output tax position per period with a filed-amendment worksheet, DRC-03 top-up trigger for short payments, and audit-ready evidence pack mapping every GSTR-1 invoice to its GSTR-3B contribution.
Why GSTR-1 and GSTR-3B Must Agree
GSTR-1 is an invoice-level declaration: every B2B invoice, credit note, and debit note raised during the month must be reported with the recipient’s GSTIN, invoice number, taxable value, and GST amount. GSTR-3B is a summary self-assessment: the taxpayer declares total output tax liability and pays it. These are two different instruments reporting the same underlying fact — how much output tax the business collected during the period — and they must produce the same total.
When they disagree, the discrepancy is one of four types: GSTR-1 is higher than 3B (short payment of tax), GSTR-1 is lower than 3B (excess payment — less common but creates ITC issues for recipients), invoices appear in GSTR-1 for a different period than they appear in 3B, or credit notes reduce GSTR-1 liability but are not reflected in 3B. The GSTR-2B reconciliation guide covers the recipient-side ITC impact when these mismatches occur at the supplier.
The Nine-Day Reconciliation Window
Monthly filers face GSTR-1 on the 11th and GSTR-3B on the 20th. That nine-day gap is the natural checkpoint. The process:
- File GSTR-1 by the 11th, ensuring all invoices for the month are uploaded
- Download the GSTR-1 summary from the GST portal and extract the total output tax by rate slab (5%, 12%, 18%, 28%)
- Reconcile this against the sales register total for the same period
- Carry forward any amendments from the prior period’s GSTR-1 that affect the current 3B liability
- Arrive at the correct 3B output tax figure before filing on the 20th
Skipping this step and filing 3B using an internal estimate — without checking GSTR-1 — is the primary cause of recurring mismatches.
Types of GSTR-1 vs GSTR-3B Mismatches
| Mismatch Type | Typical Cause | Resolution | Compliance Risk |
|---|---|---|---|
| GSTR-1 output tax > 3B tax paid | 3B filed using an understated estimate | Pay differential + 18% pa interest via DRC-03 | High — ASMT-10 scrutiny, DRC-01 demand |
| GSTR-1 output tax < 3B tax paid | Overcalculated 3B or credit note missed in 3B | Adjust excess in next period’s 3B; credit note to appear in GSTR-1 | Low — excess tax paid; ITC impact on recipient |
| Invoice period mismatch | Invoice raised in March but reported in April GSTR-1 | File amendment in Table 9A; align 3B period | Medium — interest on delayed GSTR-1 reporting |
| GSTR-1 amendment not in 3B | Table 9A amendment filed but 3B not adjusted | Adjust the amended differential in next 3B | Medium — cumulative mismatches grow over quarters |
| Credit note in GSTR-1 missing from 3B | Credit note reported in GSTR-1 Table 9B but 3B unchanged | Adjust credit note tax reversal in next 3B | Medium — overstated 3B liability compounding |
Amendments and Their Effect on Reconciliation
GSTR-1 amendments are filed in the return period when the correction is made, not the period of the original invoice. This creates a timing mismatch that must be tracked explicitly. If a March invoice is amended in April’s GSTR-1, the April GSTR-3B must reflect both the current month’s output tax and the amendment differential.
Automated tracking of running amendment balances across periods is part of GSTR-1 / GSTR-3B outward reconciliation, which leads the roadmap for reconciliation software India. For businesses using spreadsheets, the amendment log must be maintained manually — one missed amendment can cascade into a six-month reconciliation problem.
The GSTR-2A vs GSTR-2B difference is relevant here from the recipient’s side: when a supplier amends an invoice in GSTR-1, the amendment reflects in the recipient’s GSTR-2B for the amendment period, not the original invoice period. Both sides of the transaction carry reconciliation implications.
GSTN Scrutiny and DRC-01 Notices
GSTN’s ADVAIT analytics engine compares GSTR-1 and GSTR-3B values at the taxpayer level every month. Discrepancies above the threshold for the taxpayer’s risk category trigger an ASMT-10 scrutiny notice. The taxpayer has 30 days to respond with a reconciliation statement and explanation.
If the response is unsatisfactory — or if no response is filed — a DRC-01 demand notice is issued, specifying the tax demand, interest at 18% per annum from the original due date, and applicable penalties. Penalties for non-fraudulent mismatches are typically 10% of the tax amount; for cases where suppression of invoices is alleged, penalties can reach 100%.
The most effective defence against scrutiny is a documented, timestamped reconciliation for every period — showing that differences were identified, investigated, and resolved. Generating this audit trail automatically is part of GSTR-1 / GSTR-3B outward reconciliation, which leads the roadmap for GST reconciliation software. A spreadsheet-based process does not produce it.
Quarterly Filers Under QRMP
Taxpayers under the QRMP scheme file GSTR-1 quarterly but pay tax monthly via PMT-06. The reconciliation logic changes: each month’s PMT-06 payment must be validated against estimated output tax for that month, and the quarterly GSTR-1 must reconcile with the sum of three months’ PMT-06 payments. GSTR-3B is filed quarterly by QRMP taxpayers, so the reconciliation window extends but the exposure accumulates if the estimate is consistently wrong.
For the e-invoice reconciliation workflow, e-invoices generated during the quarter auto-populate GSTR-1 upon generation — but the PMT-06 payments must still be checked against accumulated e-invoice output tax each month to avoid a large reconciliation gap at the quarterly 3B stage.