India GST Compliance Guide (FY 2025–26): Double-Entry Posting, GSTR-1, GSTR-2B Reconciliation, GSTR-3B & GSTR-9/9C

By LedgerMapz Tax & Accounting Engineering Team • Reviewed against official CBIC / FTA / IRS rules • Back to Knowledge Hub

Table of Contents: 1. GSTIN Structure & Modulo-36 Checksum • 2. Double-Entry Voucher Posting for CGST, SGST, IGST & RCM • 3. GSTR-1 Outward Supplies & HSN Rules • 4. GSTR-2B vs Purchase Register Reconciliation & Section 16(2)(aa) ITC • 5. GSTR-3B Monthly Settlement & Annual GSTR-9/9C Audit Reconciliation.

1. Understanding 15-Digit GSTIN Structure & Place of Supply

Every registered Indian taxpayer is assigned a 15-character Goods and Services Tax Identification Number (GSTIN): the first 2 digits represent the State Census Code (e.g., 27 for Maharashtra, 29 for Karnataka), digits 3–12 are the 10-character PAN, digit 13 is the entity registration number within the state, digit 14 is Z, and digit 15 is a Modulo-36 check character. Under Section 10 and Section 12 of the IGST Act, 2017, when the Supplier State Code matches the Place of Supply State Code, the transaction is Intra-State and attracts equal CGST + SGST. When the state codes differ (or for exports/SEZ supplies), the transaction is Inter-State and attracts IGST.

2. Worked Double-Entry Example (Intra-State vs Inter-State & Reverse Charge)

Suppose a Bengaluru company (State 29) sells taxable IT hardware worth ₹1,00,000 at 18% GST to a customer in Mysuru (State 29):

• Dr Sundry Debtor (Customer A/c): ₹1,18,000.00
• Cr Sales — Domestic Taxable (18%): ₹1,00,000.00
• Cr Output CGST (9%): ₹9,000.00
• Cr Output SGST (9%): ₹9,000.00

For Goods Transport Agency (GTA) or legal services attracting Reverse Charge Mechanism (RCM) under Section 9(3), the recipient must discharge the tax in cash via the Electronic Cash Ledger first and can then claim eligible Input Tax Credit.

3. GSTR-2B Reconciliation & Input Tax Credit (ITC) Rules

Under Section 16(2)(aa) of the CGST Act read with Rule 36(4), a taxpayer can avail Input Tax Credit in Form GSTR-3B only when the supplier has furnished the invoice in their Form GSTR-1/IFF and the invoice appears in the recipient’s static statement Form GSTR-2B generated on the 14th of the succeeding month. LedgerMapz classifies every purchase voucher into four buckets: Exact Match, Tax Value Mismatch, In Books but Missing in 2B (hold ITC & notify supplier), and In 2B but Missing in Books.

4. Managed GST Compliance Service vs Self-Filing

Indian tenants on LedgerMapz can export JSON/Excel files for self-filing or activate our Managed GST Compliance Service (₹2,500/mo or ₹24,000/yr), where an assigned GST Practitioner / Chartered Accountant prepares GSTR-1, reconciles GSTR-2B, reviews blocked credits under Section 17(5), and files only after you click Approve Figures in your dashboard.