GSTR-1 outward tax + GSTR-2B ITC reconciled into a validated return — GST return automation in under 30 seconds per period.
| Period | Supply Type | Taxable Value (Rs) | CGST (Rs) | SGST (Rs) | IGST (Rs) |
|---|---|---|---|---|---|
| Feb-2026 | B2B Intra-State | 50,00,000 | 4,50,000 | 4,50,000 | 0 |
| Feb-2026 | B2B Inter-State | 12,00,000 | 0 | 0 | 2,16,000 |
| Feb-2026 | B2C Large | 3,50,000 | 31,500 | 31,500 | 0 |
Preparing a monthly GSTR-3B return manually takes a mid-market accounts team anywhere from half a day to two full working days per GSTIN — and every step is a compounding source of error that the GST portal will not catch until the return is filed.
The controller must open the GSTR-1 summary, aggregate outward supply taxable values and tax breakups by supply type, cross-reference the GSTR-2B auto-populated ITC statement head by head, and manually key the results into Table 3.1 and Table 4. At 50–200 supply rows per month, transposition risk is material on every row.
Section 49 of the CGST Act prescribes a mandatory ITC utilisation sequence — IGST credit first against IGST liability, then against CGST, then against SGST/UTGST — before head-specific credits are applied. Computing this waterfall correctly in a spreadsheet, while simultaneously capping ITC against GSTR-2B figures under Rule 36(4), demands parallel lookups that are error-prone under time pressure.
For intra-state supplies, Section 9 of the CGST Act and the mirroring SGST Acts require CGST and SGST to be levied at identical rates. A data entry error producing unequal amounts will not be caught by the GST portal until filing — at which point a revised return or rectification in a subsequent period becomes the only remedy. For companies filing across multiple GSTINs, this error class multiplies proportionally.
Uploading a GSTR-2B for November against a GSTR-1 for December populates the 3B working with mismatched ITC — an error that can result in excess ITC utilisation and subsequent demand notices under Section 73 or Section 74 of the CGST Act. The discipline is easy to break when files arrive by email across multiple days.
The annual interest rate on wrongly availed and utilised ITC under Section 50(3) of the CGST Act. For a company with Rs 20–50 lakh of monthly ITC, a 2% overclaim — entirely possible when copying figures manually from GSTR-2B — produces a material interest liability within a single financial year, in addition to the principal demand and potential penalty under Section 74.
GSTR-3B is not a supplementary return — it is the primary monthly self-assessment return under Indian GST. Four statutory anchors govern how it must be prepared, and each one creates a hard validation obligation the workflow enforces deterministically.
Every GST-registered taxpayer (outside the QRMP scheme) must file GSTR-3B by the 20th of the following month. The return consolidates outward supplies from GSTR-1 into Table 3.1 and eligible input tax credit from GSTR-2B into Table 4 — making the reconciliation of these two documents a mandatory step, not a best-practice recommendation.
Inserted by the Finance Act 2021, this provision restricts ITC to amounts reflected in the supplier’s GSTR-1 as auto-populated in GSTR-2B. Since the October 2022 portal change, Table 4 is pre-filled from GSTR-2B and any deviation is flagged by the portal — making the ITC cap a formal compliance step rather than an optional check.
IGST credit must be applied first against IGST liability, then against CGST, then against SGST/UTGST before head-specific credits are applied. Computing this waterfall out of sequence understates net liability on one head and overstates it on another — a classification error that survives the portal’s arithmetic checks but triggers interest and penalty on audit.
CGST and SGST are levied at identical rates on every intra-state supply. A parity break — CGST Rs 4,50,000 vs SGST Rs 4,25,000 — violates this requirement across every state’s SGST Act simultaneously. The ICAI’s Technical Guide on GST Audit (2023) lists CGST/SGST asymmetry as one of the top five findings under Section 65 departmental audits.
Seven deterministic passes from GSTR-1 + GSTR-2B uploads to a validated, export-ready GSTR-3B working — in under 30 seconds per period, with five hard validation checks replacing manual cross-referencing across three separate statutory obligations.
The worker accepts two Excel (.xlsx) uploads and identifies each by column-header signature: the GSTR-1 Summary (Period, Supply Type, Taxable Value, IGST, CGST, SGST, Cess) and the GSTR-2B Summary (Period, ITC Category, Taxable Value, IGST ITC, CGST ITC, SGST ITC, Cess ITC). No template mapping is required; classification is automatic.
Before any table population, the workflow compares the period field across both documents. A mismatch — e.g. GSTR-1 for Dec-2025 against GSTR-2B for Nov-2025 — raises an immediate FAIL on the Period Match check and halts further processing, preventing silent ITC miscalculation from reaching the return.
Outward supply rows are aggregated by supply type (B2B Intra-State, B2B Inter-State, B2C Large, SEZ, Export, Nil-Rated) and mapped to the corresponding sub-columns in Table 3.1(a) and 3.1(b) of GSTR-3B. Taxable values and tax amounts are carried over exactly from GSTR-1, with no rounding beyond the Rs 1 tolerance.
For every intra-state supply row, the workflow asserts CGST = SGST to within Rs 1, enforcing the requirement under Section 9 of the CGST Act. A discrepancy raises a FAIL on the CGST SGST Equal check with the exact variance amount flagged. Inter-state rows where both CGST and SGST are zero are automatically marked not-applicable, preventing false positives.
Eligible ITC from GSTR-2B is mapped into Table 4 by head (IGST ITC, CGST ITC, SGST ITC) and by category (All Other ITC Eligible, Imports, Reverse Charge, ISD). Any book-side ITC claim exceeding the auto-populated GSTR-2B figure on any single head raises a FAIL on the ITC Within 2B Limit check, enforcing Rule 36(4) of the CGST Rules.
Net tax payable is computed by applying available ITC in the statutory sequence prescribed under Section 49 read with Rule 88A: IGST credit first against IGST liability, then against CGST, then against SGST/UTGST — before CGST and SGST credits are applied to their respective heads. The workflow asserts that no net liability head produces a negative balance; excess credit is carried forward, never understated.
On all-pass, the workflow writes a structured Excel workbook with four tabs: the completed Table 3.1 working, the Table 4 ITC working, the Section 49 set-off waterfall schedule, and a validation summary. The file is stamped with the entity name, GSTIN, period, and run timestamp — formatted to drop directly into the controller’s monthly GST compliance folder or auditor working-paper file.
A battery of synthetic test scenarios that exercise every failure mode we have seen in real-world GSTR-3B preparation. Each scenario produces a deterministic outcome an auditor or controller can verify in seconds.
Two seeded sample files that together exercise the full range of validation scenarios — clean lines, ITC overclaims, CGST/SGST breaks, period-drift credit, and ineligible ITC.
One consolidated Feb-2026 outward-supplies register across intra-state (CGST + SGST), inter-state (IGST), B2C, SEZ, export and nil-rated buckets. Most lines reconcile cleanly; one intra-state line plants a CGST/SGST parity break of Rs 25,000 to exercise the Section 9 check.
Matching Feb-2026 GSTR-2B ITC register across All-Other-ITC, imports, reverse charge, ISD, capital goods, and Section 17(5) ineligible buckets. Planted exceptions: an ITC over-claim above auto-populated value, a credit line tagged to a different period, a taxable-value delta beyond Rs 1 tolerance, and an ineligible Section 17(5) credit still claimed as eligible.
Running the workflow against the consolidated Feb-2026 pair produces a fully prepared GSTR-3B working in under 30 seconds — with five validation checks catching every planted exception before any figure reaches the return.
The Feb-2026 run across ~62 GSTR-1 outward lines and ~58 GSTR-2B ITC lines extracts every row, validates each summary, and reconciles the two for the period. The deliverable is a prepared GSTR-3B return surfaced on the GSTR-3B Returns view: Table 3.1 rolls the GSTR-1 outward tax into three heads (CGST Rs 4,81,500, SGST Rs 4,81,500, IGST Rs 2,16,000), Table 4 maps eligible ITC head-wise from GSTR-2B, and the Section 49 set-off waterfall nets the two to produce a net tax payable of Rs 6,57,000 across heads. Output tax that exceeds eligible credit on a head becomes payable; where credit exceeds output tax the head is floored at zero and the excess carries forward, never going negative.
The bulk of the Feb-2026 lines reconcile cleanly, while four planted exceptions exercise the full validation taxonomy. The intra-state line where CGST Rs 4,50,000 diverges from SGST Rs 4,25,000 triggers a FAIL on the Section 9 parity check with the Rs 25,000 variance flagged. An IGST ITC claim padded above the GSTR-2B auto-populated value triggers FAIL on Rule 36(4) ITC Within 2B Limit. A credit line tagged to a different tax period is excluded from eligible ITC and surfaced as a period-drift exception. A Section 17(5) ineligible credit — blocked ITC on motor-vehicle expenses — is stripped from Table 4 and counted in the exceptions queue. The worker excludes all four breaks from the Table 4 eligible totals: the prepared return shows 4 reconciliation exceptions flagged, representing a recoverable-demand exposure with 24% per annum interest under Section 50(3) of the CGST Act had any of these credits flowed unchecked into the filed 3B.
The GSTR-3B Auto-Prep workflow reduces a task that typically consumes 4–8 person-hours per month per GSTIN to under 30 seconds, with five hard validation checks replacing manual cross-referencing across three separate statutory obligations simultaneously.
Period mismatches, ITC overclaims, and CGST/SGST asymmetries are caught by deterministic FAIL checks before any figure reaches the 3B export — not by a portal error after filing. This eliminates the revised return or subsequent-period rectification that Section 73 and Section 74 demand notices would otherwise require, together with their 24% per annum interest exposure under Section 50(3).
The Excel export contains the Table 3.1 working, the Table 4 ITC working, the Section 49 set-off waterfall, and the validation summary in separate tabs — all referenced back to source GSTR-1 and GSTR-2B inputs, entity name, GSTIN, period, and run timestamp. This file meets the documentation expectations of a GST audit under Section 65 of the CGST Act without any additional formatting step.
For companies with registrations in multiple states — each holding a separate GSTIN under Section 25 of the CGST Act — error reduction is structural rather than probabilistic. Running five GSTINs means five deterministic checks per head per period, not five times the manual reconciliation risk. The inbox organises returns by period label and entity name so a multi-entity controller sees all monthly statuses in a single view.
The questions controllers and tax teams ask most often before deploying automated GSTR-3B preparation.
Two files for the same tax period: your GSTR-1 outward-supplies summary (the sales register backing the GSTR-1 return) and your GSTR-2B ITC summary (the auto-populated input-tax-credit statement from the GST portal). Both are tabular .xlsx files; drop them together and Cadel classifies each automatically by column-header signature — no template mapping required.
A prepared GSTR-3B return for the period. It rolls the GSTR-1 outward tax into Table 3.1, the eligible GSTR-2B credit into Table 4, nets the two per tax head (IGST, CGST, SGST) and gives you the net tax payable — ready to review on the GSTR-3B Returns view before you file. On successful completion, an Excel workbook with four tabs (Table 3.1 working, Table 4 working, Section 49 set-off waterfall, validation summary) is available for export.
Output tax from GSTR-1 less eligible input tax credit from GSTR-2B, computed separately for IGST, CGST and SGST and floored at zero per head (excess credit carries forward, it never goes negative). The Section 49 set-off waterfall applies IGST credit first against IGST liability, then against CGST, then against SGST/UTGST — before CGST and SGST credits are applied to their respective heads. The three net heads add up to the total net tax payable shown on the return.
Every GSTR-2B line except two kinds: credit blocked under Section 17(5) of the CGST Act (Ineligible ITC — motor vehicles, food, club memberships, health services, and similar blocked items) and any line tagged to a different tax period than the return. Those are excluded from the Table 4 eligible totals and surfaced as exceptions, so your claimed ITC stays within the Rule 36(4) auto-populated cap.
Five exception classes, each corresponding to a statutory check: (1) intra-state lines where CGST does not equal SGST (Section 9); (2) ITC claimed above the GSTR-2B auto-populated value on any head (Rule 36(4) over-claim); (3) credit lines belonging to a different tax period; (4) taxable-value differences between GSTR-1 and GSTR-2B beyond the ±Rs 1 tolerance; and (5) Section 17(5) ineligible credit still carried as eligible. Each appears in the Exceptions queue with the specific line, the reason code, and the variance amount.
GSTR-3B is filed per tax period, so the outward liability and the input credit have to belong to the same month. Section 39 of the CGST Act mandates a single self-assessed summary per period. If a GSTR-2B line carries a different period the workflow flags it rather than silently mixing periods, which would understate or overstate the net liability on the return and trigger a reconciliation discrepancy during the annual GSTR-9 filing or a departmental scrutiny under Section 61.
The workflow ingests standard Excel (.xlsx) files in the column layout used by the GSTN offline utilities and most Indian accounting packages, including Tally Prime’s GSTR-1 export and Zoho Books’ supplier ITC reports. No API connection to the GST portal or a specific ERP is required; users download the GSTR-1 and GSTR-2B summaries from the portal or their accounting software and upload them directly. The output Excel workbook is formatted as a GSTR-3B working sheet, cross-checkable before manual entry into the GST portal.
No. Your GSTR-1 and GSTR-2B data is processed only to prepare this GSTR-3B return for the period in question. The documents are never used to train any model, shared with third parties, or retained beyond the audit-trail retention period. Every run produces a timestamped immutable record stored in the Cadel inbox against the monthly period, exportable as a PDF or Excel artefact for GSTR-9 annual reconciliation or departmental scrutiny under Section 65 of the CGST Act.
