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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.
For businesses running reconciliation software India that tracks running amendment balances across periods, this is automated. 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. Purpose-built GST reconciliation software generates this audit trail automatically. A spreadsheet-based process does not.
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.