GSTR-1 vs GSTR-3B Runbook: The Final Five-Day Sequence Before Month-End Filing

Days 16 to 20 of the monthly reconciliation cadence are the window where the four earlier streams are assembled into GSTR-3B and filed. The compression that most Indian finance teams experience on the eighteenth, nineteenth, and twentieth of every month is not because GSTR-3B is a hard return to file — it is because bank exceptions from Days 1 to 5, TDS residuals from Days 6 to 10, and GSTR-2B ITC categorisation debt from Days 11 to 15 all land on the GST executive’s desk simultaneously in the closing window. This runbook is the day-by-day sequence for closing the cadence cleanly, catching the DRC-01B intimation trigger before Rule 88C fires it, and filing at 11am on the 20th rather than at 11:47pm.

The window has two constraints that shape everything inside it. GSTR-1 is due by the eleventh of the following month. GSTR-3B is due by the twentieth. The gap between the two dates is where the reconciliation happens — the outward supply figures were locked when GSTR-1 was filed, the ITC ceiling was locked when the Day 15 GSTR-2B sign-off happened, and the closing window carries the assembly and the cross-stream reconciliation. If either constraint is missed, the notice cascade begins. If both are met with the cadence run cleanly, the month closes against a defensible audit trail that a subsequent Section 73 or Section 74 assessment can be defended against without reconstructing the calculation years later.

Prerequisites — what must be true before Day 16

Day 16 does not start from a blank page. The window carries three signed-off working papers from the earlier cadence and a filed GSTR-1 as its inputs.

• Day 5 bank sign-off. The finance manager has signed off the bank reconciliation. Every unreconciled item is in the exception queue with an owner, an age, and an escalation rule.
• Day 10 TDS sign-off. The tax manager has signed off the TDS reconciliation. The Table 6.2 Section 51 TDS figure that will populate GSTR-3B is fixed. The TDS runbook documents the Day 6 to 10 cadence that produces this handoff.
• Day 15 GSTR-2B sign-off. The controller has signed off the ITC figure that will populate GSTR-3B Table 4. The at-risk queue against the Section 16(4) November 30 deadline is running. The GSTR-2B runbook documents the Day 11 to 15 cadence and the five-bucket categorisation the Day 15 sign-off rests on.
• GSTR-1 filed by the eleventh. The GST executive has filed GSTR-1 on the portal before the statutory deadline. The filing receipt with the acknowledgement reference is in the monthly folder.

If any of the three sign-offs are missing, Day 16 cannot start cleanly. The window either re-opens the earlier cycle or documents a scope reduction — filed against a provisional working paper with a written escalation note on the controller’s desk. There is no third option; running Day 16 to 20 against unsigned working papers is what produces the 11:47pm filing.

The owner map for the window

The window carries three named roles.

• The GST executive runs the sequence. GSTR-1 reconciliation, Table 3.1 variance categorisation, GSTR-3B assembly across Tables 3, 4, 5, 6.1, and 6.2, amendment tracker maintenance, challan preparation for cash-ledger offset.
• The tax manager reviews. Independent review on Day 19 covering the four cross-stream tolerance checks, the amendment table completeness against Section 39(9), and the challan-to-ledger reconciliation.
• The controller signs off. The signature on Day 20 releases the filing. The controller signs because Section 74 attaches a penalty of one hundred per cent of the tax amount for fraudulent shortfall, and the classification between Section 73 non-fraudulent (three-year window, no proportional penalty) and Section 74 fraudulent (five-year window, hundred per cent penalty) turns on documentary evidence of the person who signed.

The reconciliation process design method that sits above this runbook makes the sign-off level a hard rule — where a Section 74 exposure sits behind a function, the sign-off must be at the level of executive accountability, not at the level of process ownership. The failure-anchored design layer for this window is documented in the GSTR-1 versus GSTR-3B failure modes article; this runbook is how the design gets executed. The two are bidirectional — read one alongside the other.

Day 16 — GSTR-1 filing recap and output register extraction

Day 16 exists to confirm that GSTR-1 has been filed by the eleventh and to extract the ERP output GST register that the Day 17 reconciliation will run against. If the closing window starts on the sixteenth of the month, GSTR-1 has been filed five days earlier — the executive confirms the acknowledgement, downloads the filed return from the GSTN portal, and extracts the ERP output GST register dated to the last calendar day of the closed month.

The GST executive opens the GSTN portal, navigates to Returns Dashboard, selects the closed month, and downloads the filed GSTR-1 as JSON and PDF. The JSON is the reconciliation input; the PDF is the audit-trail archive.

• B2B invoice detail. Every invoice raised to a registered recipient with GSTIN, invoice number, invoice date, taxable value, tax rates, and the CGST/SGST or IGST split.
• B2C large invoice detail. Every invoice above the state-wise value threshold to an unregistered recipient with place of supply, taxable value, and tax split.
• B2C consolidated summary. State-wise summary of B2C small invoices.
• Export invoice detail. Every export invoice classified as either under LUT-without-payment or with-payment-of-IGST-then-refund. The classification is what drives the Table 6A refund reconciliation loop.
• Credit note and debit note detail. Every credit note or debit note issued in the closed month, keyed to the original invoice being adjusted.
• Amendment tables 9A, 9B, 9C. Every amendment made to a prior-period B2B invoice, credit note, or B2C large invoice.

The ERP output register is extracted from the finance system for the same period. The extract carries every outward invoice with invoice number, invoice date, GSTIN of recipient (or place of supply for B2C), taxable value, tax rates, CGST, SGST, IGST, and cess. Both extracts are archived in the monthly folder with a timestamp and a hash. Both go into the Day 17 working paper.

Day 17 — Table 3.1 GSTR-1 versus internal register reconciliation

Day 17 is the heart of the window. The GST executive runs the Table 3.1 reconciliation — GSTR-1 declared outward supply versus ERP output GST register — and categorises every variance into one of five mutually exclusive buckets. Every invoice in the GSTR-1 or the ERP register must land in exactly one bucket, and every bucket has a documented downstream action.

Bucket 1 — In GSTR-1 and in ERP register (matched)

The invoice is declared in GSTR-1 for the closed month and appears in the ERP output register for the same month. The taxable value, tax rate, and tax split match. This is the population that flows straight into GSTR-3B Table 3.1 as declared outward liability. Expect 85 to 95 per cent of the closed month’s invoice value to land here for a team with a disciplined GSTR-1 filing cadence.

Bucket 2 — In GSTR-1, not in ERP register

The invoice is declared in GSTR-1 but is not booked in the ERP register for the same month. Two very different causes drive this bucket and both are investigated on the same day. Cause A is a wrong-period ERP posting — the invoice was raised on the last day of the closed month but posted to the following month’s register due to a cutoff error. The resolution is to correct the ERP posting date so the register catches up. Cause B is a GSTR-1 wrong-period declaration — the invoice belongs to the previous month but was declared in the closed month’s GSTR-1 to catch up an earlier filing gap. The resolution is to document the wrong-period declaration and flag it against the amendment tracker for Table 9A treatment in a subsequent GSTR-1 if a correction is needed.

Bucket 3 — In ERP register, not in GSTR-1

The invoice is booked in the ERP register but is not declared in the closed month’s GSTR-1. This is the most dangerous bucket in the window. The invoice belongs to the closed month, was raised to a real recipient, has generated the corresponding output tax liability in the ERP — but was not declared. Three causes are common. Cause A is a mid-month GSTIN master update that broke the GSTR-1 pipeline. Cause B is a credit note issued in the closed month that was applied to the ERP but not declared in GSTR-1 Table 9B. Cause C is an export invoice classified incorrectly at the ERP level and skipped by the GSTR-1 filter for export invoices. The resolution is to declare the invoice in the following month’s GSTR-1 through Table 9A (for B2B invoices) or Table 9B (for credit and debit notes) — subject to the Section 39(9) November 30 amendment cutoff. Any invoice from an April filing that misses declaration by November 30 of the following financial year cannot be added through the amendment tables and becomes a Section 73 or Section 74 exposure.

Bucket 4 — Rate or value variance (invoice in both, tax figures differ)

The invoice appears in both GSTR-1 and the ERP register, but the taxable value or the tax rate or the tax split differs. Common causes are a rate revision applied to the ERP after the invoice was raised but before GSTR-1 filing (the two snapshots drift); a currency-conversion difference on an IGST invoice denominated in a foreign currency; or a rounding difference in the tax figure. Each is investigated on Day 17 and either corrected in a subsequent GSTR-1 amendment or documented as an accepted variance within the DRC-01B tolerance band under Rule 88C.

Bucket 5 — Credit note timing drift

A credit note issued in the closed month against an invoice raised in an earlier month. The credit note is booked in the ERP register for the closed month but must be declared in GSTR-1 Table 9B for the closed month keyed to the original invoice’s month and financial year. Under Section 34, the credit note must be declared by the earlier of November 30 following the end of the financial year in which the original supply was made or the date of the annual return. If the closed month is October and the original invoice is from March of the previous financial year, the credit note has one filing window left before the Section 34 window closes.

The Day 17 categorisation table is the working paper’s primary deliverable. Every invoice count reconciles — GSTR-1 total equals Bucket 1 plus Bucket 2 plus Bucket 4 (variance sub-population), and ERP register total equals Bucket 1 plus Bucket 3 plus Bucket 5. Any reconciliation gap in the totals is a bug in the working paper and must be resolved before the Day 18 GSTR-3B assembly begins.

Day 18 — GSTR-3B assembly from four signed-off working papers

Day 18 is assembly, not calculation. Every table in GSTR-3B pulls from a signed-off working paper from an earlier window in the cycle. Nothing in GSTR-3B is calculated for the first time on Day 18. This is the discipline that separates a defensible filing from a fingers-crossed filing.

Table 3.1 — Outward supplies and inward supplies liable to reverse charge

Populated from the Day 17 reconciliation. Every rupee in Table 3.1 traces back to either the Bucket 1 matched population or an explicit Bucket 2/3/4/5 handling rule. Zero-rated supplies (exports and SEZ) are broken out from taxable outward supplies. The reverse charge inward supply line is populated from the ERP AP register cross-referenced to the GSTR-2B reverse-charge extract.

Table 4 — Eligible ITC

Populated from the Day 15 GSTR-2B controller sign-off. The GSTR-2B runbook produces a one-page working paper carrying the bucket reconciliation and the four reversal and block workings. Table 4 pulls from that working paper. No recalculation is done on Day 18.

Table 5 — Exempt, nil-rated, non-GST inward supply

Populated from the Day 14 exempt-turnover working paper produced during the Rule 42 and 43 common-credit reversal exercise in the GSTR-2B window.

Table 6.1 — Payment of tax

Populated from the Day 17 outward liability minus the Day 15 ITC ceiling. The residual is the cash-ledger payment required for the month. The GST executive prepares the challan on Day 18 for deposit in the electronic cash ledger. The challan must be credited to the ledger before the 11am Day 20 filing; the electronic cash and credit ledger can take up to an hour to reflect a fresh challan, so the Day 18 deposit builds in the ledger-refresh buffer.

Table 6.2 — TDS and TCS credit

Populated from the deductor’s GSTR-7 filing (for Section 51 GST TDS at two per cent — one per cent CGST plus one per cent SGST, or two per cent IGST — deducted by government departments, PSUs, and notified categories on supplies above two lakh fifty thousand rupees) and the e-commerce operator’s GSTR-8 filing (for Section 52 TCS at one per cent — half per cent CGST plus half per cent SGST, or one per cent IGST — on the net value of taxable supplies made through the platform). The Day 10 TDS handoff pre-populates the expected credits; Day 18 confirms them against the deductor filings.

Table 3.1(d) — Reverse charge inward liability

Populated from the reverse-charge inward supply working paper — freight paid to a goods transport agency, security services from a security agency, sponsorship services, and other notified categories where the recipient is liable to pay GST under reverse charge. The corresponding ITC (subject to Section 17(5) blocks) is claimed in Table 4.

The Day 18 assembly is complete when every table has a documented trace to a signed-off working paper and the challan is prepared for the cash-ledger offset. The file is handed to the tax manager for Day 19 independent review.

Day 19 — Independent review and the four cross-stream tolerance checks

Day 19 is the last inspection before the controller signs the filing on Day 20. The tax manager runs an independent review of the Day 18 assembly and covers four cross-stream tolerance checks that no single window in the cycle can catch by itself.

Cross-stream check 1 — Bank credits minus TDS receivable versus ERP revenue

Bank credits from the Days 1 to 5 window minus TDS receivable movement from the Days 6 to 10 window should tie to ERP revenue for the closed month within a defined tolerance (typically five basis points for a stable business, wider for aggregator-heavy models). A gap wider than the tolerance is either a bank reconciliation exception the Day 5 sign-off missed or an ERP revenue-recognition anomaly (multi-currency drift, milestone-billing timing, deferred revenue mis-classification).

Cross-stream check 2 — ERP output GST versus GSTR-1 declared liability

The Day 17 reconciliation output is re-checked at Day 19 against a fresh ERP pull. Any invoice booked or amended between Day 17 and Day 19 that changed the output GST total must either be corrected on the portal through the amendment window or be documented as a wrong-period entry to be declared in a subsequent GSTR-1.

Cross-stream check 3 — GSTR-3B ITC versus purchase register within Rule 36(4)

The Day 15 signed-off ITC figure is checked against a fresh purchase register extract at Day 19 to catch any invoices booked between the two dates. Under Rule 36(4), the claim cannot exceed the GSTR-2B figure — so any additional purchase register invoices that landed in GSTR-2B on the fifteenth but were booked in the ERP between the fifteenth and the nineteenth need to be excluded from the current cycle’s claim and deferred to the following month’s ITC.

Cross-stream check 4 — Section 51 GST TDS versus deductor GSTR-7 credit

The Section 51 GST TDS figure the recipient expects to receive as a credit is re-checked against the deductor’s GSTR-7 filing on the twelfth of the following month. Any deductor who filed late or short-deducted or wrong-GSTIN-ed the deduction produces a GSTR-2A/2B mismatch on the recipient’s TDS credit line, which becomes a Table 6.2 shortfall in the current GSTR-3B.

Where any of the four tolerance checks fails, the exception is escalated to the controller before Day 20 sign-off. The tax manager cannot approve a filing whose cross-stream tolerance is breached — the escalation goes to the controller with a documented recommendation (file under a provisional note, defer amendment to next cycle, re-run the affected window). Anything the reviewer cannot trace back to a signed-off working paper is escalated in the same way.

Day 20 — Controller sign-off and the 11am filing

Day 20 morning closes the window. The controller signs the GSTR-3B filing at 8am after a final ledger check and the file is submitted on the portal by 11am. The four-hour buffer between the 8am signature and the 11am filing is what allows a portal issue, a payment lag, or a last-minute correction to be handled without missing the statutory deadline.

The 8am ledger check covers three items. First, the electronic cash ledger reflects the Day 18 challan in full. If the ledger is short, the executive re-runs the challan or top-ups from another cash-ledger balance. Second, the electronic credit ledger reflects the Day 15 signed-off ITC figure. If any Rule 37 or Rule 37A reversal was triggered between Day 15 and Day 20 (a supplier’s 180-day non-payment threshold crossed, a supplier’s GSTR-3B non-filing surfaced), the reversal is applied on the credit ledger and Table 4 is adjusted downward. Third, any DRC-01B or DRC-01C intimation that fired between the Day 19 review and the Day 20 filing is checked on the portal — a fresh intimation may require a reply during the seven or thirty-day window that overlaps with the Day 20 filing.

The controller’s signature is applied on the portal using the authorised digital signature (director’s DSC or authorised representative’s DSC under Section 25 of the Information Technology Act 2000). The filing acknowledgement is downloaded, timestamped, and archived in the monthly folder. The window closes.

Under Section 122, the penalty for issuing an incorrect or false invoice, collecting tax without depositing it beyond three months, or availing ITC without actual receipt of goods or services is ten thousand rupees or an amount equivalent to the tax evaded, tax not deducted, or short-deducted, whichever is higher. The Day 18 GSTR-3B assembly draws its integrity from the Day 15 GSTR-2B categorisation — a ghost invoice pulled into ITC through a default IMS Accept action is what most commonly exposes the recipient to Section 122 penalty, which is why the IMS action step-by-step article is standard reading before running the Day 11 window.

The five exception classes and their resolution paths

Across the Day 16 to 20 window, five exception classes account for almost every escalation.

• Wrong-period declaration. An invoice declared in a month it does not belong to. Resolution via GSTR-1 Table 9A amendment in a subsequent period, subject to the Section 39(9) November 30 deadline.
• Credit note timing drift. A credit note issued in the current month against a prior-month invoice. Resolution via GSTR-1 Table 9B in the current month keyed to the original invoice’s period, subject to the Section 34 November 30 deadline.
• Export classification error. An export invoice classified as with-payment when it should have been under LUT, or vice versa. Resolution via the Table 6A refund reconciliation loop or a Table 9A amendment.
• Section 51 TDS shortfall. A deductor filed GSTR-7 late or under-declared the deduction. Resolution via chase-the-deductor followed by Table 6.2 adjustment in a subsequent cycle when the credit lands.
• DRC-01B intimation. A GSTR-1 versus GSTR-3B mismatch beyond the Rule 88C threshold triggered an intimation. Resolution via seven-day reply either paying the differential tax with interest under Section 50 or explaining the discrepancy on the portal.

Each exception carries an owner, an age, and an escalation rule that mirrors the monthly close pillar’s escalation ladder — Tier 1 at thirty days to the finance manager, Tier 2 at sixty days to the controller, Tier 3 at ninety days for most items and reverse-calculated from the November 30 amendment cutoff for GSTR-1 and Section 34 items. The escalation clock runs on calendar dates, not on reconciliation cycles.

When the manual runbook outgrows the closing window

The Day 16 to Day 20 cadence works for a finance team with a single GSTIN, a single or dual e-commerce platform, and outward supply that fits on one Table 3.1 line item. Three thresholds break the cadence.

• Multi-GSTIN groups. Every additional GSTIN adds its own GSTR-1 filing, its own GSTR-2B pull, its own Section 39(9) amendment window, and its own DRC-01B risk surface. The Day 18 assembly compresses from a two-hour job into a two-day job, and the 11am Day 20 filing becomes untenable. The GSTR-9C three-way mismatch article documents what an unresolved multi-GSTIN amendment tracker looks like at year-end.
• Aggregator-heavy revenue models. Restaurants running four or more delivery platforms, hotels running four or more OTAs, and marketplace sellers running Amazon plus Flipkart plus one or two verticals each carry Section 52 TCS credits, platform commission GSTIN-level invoices, and reverse-charge inward supply that fragment the Day 17 reconciliation.
• High-volume export-heavy revenue. Every export invoice must be classified as LUT-without-payment or with-payment-of-IGST-then-refund. Both classifications carry a Table 6A refund reconciliation loop that the Day 18 assembly does not have room for at scale.

Above these thresholds, the runbook remains valuable as a training document and a review discipline, but the continuous reconciliation of the outward register, the amendment tracker, and the challan-to-ledger lag need to move from the analyst’s spreadsheet to a system that runs continuously rather than in a five-day window. This is the point at which Terra Insight’s GST reconciliation software installs the outward-register-versus-GSTR-1 reconciliation as a first-class continuously refreshed output against the Section 39(9) November 30 amendment clock, and the manual runbook keeps its role as the discipline the system runs against, not the process the finance team runs by hand.

Where this fits

• The Reconciliation Playbook — monthly close pillar
• GSTR-1 vs GSTR-3B reconciliation failure modes — the design layer
• GSTR-2B ITC runbook — Days 11 to 15
• TDS reconciliation runbook — Days 6 to 10
• Bank reconciliation runbook — Days 1 to 5

Related reading

• DRC-01B reconciliation reply
• Section 16(4) ITC time bar
• Invoice Management System reconciliation
• GSTR-9C three-way mismatch reconciliation
• TDS payment codes 1001-1092
• Reconciliation software for India — pillar
• GST reconciliation software

Frequently Asked Questions

What is the difference between DRC-01B under Rule 88C and DRC-01C under Rule 88D?

DRC-01B is the outward-side intimation. Rule 88C fires it when the GSTR-1 declared liability exceeds the GSTR-3B payment for the same tax period beyond a prescribed amount and percentage, and the registered person has seven days to either pay the differential tax with interest under Section 50 or explain the discrepancy on the portal. DRC-01C is the inward-side intimation. Rule 88D fires it when the ITC claimed in GSTR-3B Table 4 exceeds the ITC available in GSTR-2B beyond the Rule 36(4) ceiling, and the reply timeline is thirty days. DRC-01B is what the Day 17 GSTR-1 versus GSTR-3B reconciliation prevents; DRC-01C is what the Day 15 GSTR-2B controller sign-off prevents.

Why does the controller sign off the Day 20 filing rather than the tax manager?

Because the sign-off is on the return itself. GSTR-3B carries the digital signature of a person authorised under the CGST Act — director, partner, or an authorised representative. The tax manager can run the entire reconciliation, review the assembly on Day 19, and produce a defensible file — but the tax manager cannot carry the executive accountability that Section 74 assessment or Section 122 penalty attaches to. Section 74 attaches a penalty of one hundred per cent of the tax amount for fraudulent shortfall, and the classification between Section 73 (non-fraudulent, three-year window) and Section 74 (fraudulent, five-year window) turns on documentary evidence of the person who signed.

What are the Table 9A, 9B, and 9C amendment buckets in GSTR-1?

Table 9A carries amendments to B2B invoices originally declared in the prior period. Table 9B carries amendments to credit notes and debit notes originally declared in the prior period. Table 9C carries amendments to B2C large-invoice supplies. All three are governed by Section 39(9) — the amendment must be declared in a return for a month or quarter no later than the thirtieth day of November following the end of the financial year to which the original invoice pertains. Every credit note issued in October against a March invoice must land in Table 9B of the October GSTR-1 or be declared in the annual return — after November 30, the correction pathway closes and the residual mismatch becomes a Section 73 or Section 74 assessment matter.

Why file GSTR-3B at 11am on Day 20 rather than overnight or at 11:47pm?

Because the four-hour buffer between the Day 19 independent review and the Day 20 morning filing is what separates a defensible cadence from a fingers-crossed cadence. Overnight filing has three disadvantages — no time to correct a portal-side error, no time to react to a challan-side ledger lag, and a working paper that was signed off before the last exception check. The 11am filing is filed after the tax manager has confirmed at 8am that no overnight exception surfaced from a cross-stream review, that the electronic ledgers are current, and that the challan is fully credited. That is the discipline the cadence is built for.

When does the Day 16 to Day 20 manual runbook outgrow itself?

The cadence works for a finance team with a single GSTIN, a single or dual e-commerce platform, and outward supply that fits on one Table 3.1 line item. Three thresholds break it — multi-GSTIN groups (every additional GSTIN adds its own GSTR-1 filing, its own Section 39(9) amendment window, and its own DRC-01B risk surface); aggregator-heavy revenue models (four or more platforms fragment the Day 17 reconciliation); and high-volume export-heavy revenue (Table 6A refund reconciliation loop). Above these thresholds the runbook remains a training discipline, but the continuous reconciliation of the outward register, the amendment tracker, and the challan-to-ledger lag need to move from the analyst’s spreadsheet to a system that runs continuously against the Section 39(9) November 30 amendment clock.

Terra Insight Editorial Team Reconciliation Infrastructure

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Navin Krishnan

Managing Director & Founder — Terra Insight

Ex Amazon India · Intuit QuickBooks · Tata nexarc

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