GST Filing Process: From Invoice to Return
- The GST filing process begins when a transaction is recorded, and a correct GST invoice is issued.
- GSTR-1A can be filed once to add or correct eligible current-period records before GSTR-3B.
- Sales are reported through GSTR-1, purchase records are reviewed through IMS and GSTR-2B, and the tax liability and eligible credit are declared in GSTR-3B.
- Eligible taxpayers with turnover up to ₹5 crore may opt for quarterly filing under QRMP.
GST filing is a connected process that begins with recording a correct invoice and ends with filing the applicable return and paying the tax liability.
This guide is for GST-registered business owners and accountants who want to understand how transaction data moves from an invoice into the relevant GST returns. It mainly covers regular taxpayers. Composition taxpayers follow a different return cycle.
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How the GST Workflow Works
The sequence is easier to understand when it is viewed as one connected flow:
Invoice and accounting entry → GSTR-1 or IFF → GSTR-1A, if required → IMS and GSTR-2B → reconciliation → GSTR-3B and tax payment
An error at one stage can affect every stage that follows. For example, if a supplier enters the wrong customer GSTIN on an invoice, the transaction may not reach the correct buyer's IMS or GSTR-2B.
Step 1: Create and Record a Valid GST Invoice
The GST return process begins with the invoice. Incorrect invoice data can flow into GSTR-1 and later create mismatches for both the supplier and the buyer. The main areas of a valid GST invoice include:
| Invoice Area | Details to Verify |
|---|---|
| Supplier details | Name, address, and GSTIN |
| Invoice identity | Invoice number and invoice date |
| Recipient details | Name, address, and GSTIN or UIN, where applicable |
| Supply details | Description, quantity, HSN or SAC, and taxable value |
| Tax details | GST rate, CGST, SGST, or IGST amount, and reverse-charge indication |
| Location details | Place of supply for interstate transactions |
Invoice Area
Details to Verify
Invoice Area
Details to Verify
Invoice Area
Details to Verify
Invoice Area
Details to Verify
Invoice Area
Details to Verify
Invoice Area
Details to Verify
Under Rule 46 of the CGST Rules, the invoice number must be part of a consecutive series unique to the financial year. The law does not require every business to restart its numbering at INV-001 on 1 April.
A format such as 2026-27/001 may help separate invoices by financial year, but it is an internal control rather than a compulsory government format.
Check Whether E-Invoicing Applies
E-invoicing applies where aggregate turnover exceeded ₹5 crore in any preceding financial year from 2017-18 onward.
The business creates the invoice in its billing or accounting system and reports the prescribed details to an Invoice Registration Portal . The IRP validates the data and returns an Invoice Reference Number and signed QR code.
Taxpayers with AATO of ₹10 crore or more must report invoices, credit notes, and debit notes to the IRP within 30 days of the document date. This restriction has applied since 1 April 2025.
Example: If an eligible taxpayer issues an invoice on 1 July 2026, the document should normally be reported to the IRP by 31 July 2026.
Step 2: Report Outward Supplies in GSTR-1
Report the tax period's sales and other outward-supply details through GSTR-1 under Section 37 of the CGST Act.
What Is Reported in GSTR-1?
| Supply Type | General Reporting Treatment |
|---|---|
| B2B supplies | Reported invoice-wise with the recipient's GSTIN |
| B2C Large | Interstate supplies to unregistered recipients where the invoice value exceeds ₹1 lakh |
| Other B2C supplies | Generally reported on a consolidated basis |
| Exports and SEZ supplies | Reported invoice-wise in the applicable tables |
| Credit notes and debit notes | Reported in the prescribed note tables |
| Advances | Reported where GST applies under the applicable time-of-supply rules |
Supply Type
General Reporting Treatment
Supply Type
General Reporting Treatment
Supply Type
General Reporting Treatment
Supply Type
General Reporting Treatment
Supply Type
General Reporting Treatment
Supply Type
General Reporting Treatment
The B2C Large threshold was reduced from more than ₹2.5 lakh to more than ₹1 lakh from the August 2024 return period.
Review GSTR-1 Before Filing
Before filing, compare GSTR-1 with the sales register. The review should cover customer GSTINs, invoice numbers and dates, taxable values, GST rates, place of supply , credit notes, debit notes, e-invoice details, and B2B or B2C classification.
For example, an incorrect GSTIN may not change the total sales value, but it can prevent the invoice from reaching the correct buyer.
Step 3: Correct Eligible Errors Through GSTR-1A
Use GSTR-1A only when an eligible current-period error is identified after filing GSTR-1 but before filing GSTR-3B.
| Area | Rule |
|---|---|
| Permitted use | Add omitted current-period records or amend eligible current-period details, including eligible IFF records |
| Filing frequency | Can be filed only once for a tax period |
| Availability | Available after GSTR-1 and before GSTR-3B for the same period |
| Recipient GSTIN | Cannot be amended through GSTR-1A |
| Saved records | A saved GSTR-1A record must be deleted or reset, or GSTR-1A must be filed, before filing GSTR-3B |
| Recipient impact | ITC related to records added or amended through GSTR-1A generally appears in the recipient's next tax-period GSTR-2B |
Area
Rule
Area
Rule
Area
Rule
Area
Rule
Area
Rule
Area
Rule
Step 4: Review IMS and Reconcile GSTR-2B
The Invoice Management System allows recipients to review records reported or saved by their suppliers through GSTR-1, GSTR-1A, or IFF.
| IMS Action | General Effect |
|---|---|
| Accept | The record is considered for GSTR-2B |
| Reject | The record is excluded from eligible credit computation |
| Pending | Credit is deferred where pending treatment is permitted |
| No action | The record is generally treated as deemed accepted |
IMS Action
General Effect
IMS Action
General Effect
IMS Action
General Effect
IMS Action
General Effect
The first GSTR-2B is normally generated on the 14th of the following month. Where the record type permits it, the recipient may take an IMS action after the initial generation and recompute GSTR-2B before filing the corresponding GSTR-3B.
GSTN introduced an IMS Offline Tool in April 2026. It allows taxpayers to download IMS records, prepare actions and remarks offline, and upload the completed file to the GST Portal.
Is an Invoice in GSTR-2B Automatically Eligible for ITC?
No. Appearance in GSTR-2B is an important condition, but it does not by itself make the input tax credit eligible .
The recipient must also possess a valid tax invoice or prescribed document, receive the goods or services, file the relevant return, comply with the ITC time limit, and ensure that the credit is not blocked under Section 17(5). The payment condition relating to the supplier must also be considered where applicable.
Therefore, check the invoice, accounting entry, GSTR-2B record, and applicable legal conditions together before claiming ITC. A purchase-register entry alone is generally insufficient for a normal supplier-reported domestic invoice.
Common GSTR-2B Mismatches
| Mismatch | Likely Cause | Practical Action |
|---|---|---|
| Invoice is in the books but not in GSTR-2B | Supplier did not report it or used incorrect details | Verify the GSTIN and follow up with the supplier |
| Invoice is in GSTR-2B, but not in the books | Duplicate entry, supplier error, or unrecorded purchase | Verify the document and take the appropriate IMS action |
| Taxable value or tax amount differs | Entry error by the supplier or recipient | Reconcile the invoice and request correction |
| Credit note is missing from the books | Supplier reported a note that was not recorded | Verify and record the note before filing |
| Record is rejected or pending in IMS | Transaction details require clarification | Resolve the difference before claiming or reversing credit |
Mismatch
Likely Cause
Practical Action
Mismatch
Likely Cause
Practical Action
Mismatch
Likely Cause
Practical Action
Mismatch
Likely Cause
Practical Action
Mismatch
Likely Cause
Practical Action
For material differences, retain the invoice, purchase entry, supplier communication, goods-receipt evidence, and reconciliation explanation.
Step 5: Prepare and File GSTR-3B
After reconciling sales, purchases, IMS, and GSTR-2B, prepare GSTR-3B to declare the tax liability , eligible credit, reversals, interest, late fee, and payment for the period.
Important values are auto-populated from GSTR-1 , GSTR-1A, and GSTR-2B. However, auto-population does not remove the taxpayer's responsibility to review the figures before filing.
A taxpayer cannot file GSTR-3B for a tax period until GSTR-1 for the same period has been filed. Once GSTR-3B is filed, it cannot be revised. An error normally must be corrected on a later return or through the applicable legal process.
Paying the Remaining Tax
Output tax liability may be discharged through the Electronic Credit Ledger where ITC utilisation is permitted, the Electronic Cash Ledger, or a combination of both.
PMT-06 is the challan used to deposit funds into the Electronic Cash Ledger. It is not a separate payment ledger. Interest, late fee, penalty, and liabilities for which credit cannot be used must be paid through the Electronic Cash Ledger.
January 2026 Interest Update
From the January 2026 tax period, the GST Portal 's delayed-return interest calculation considers the minimum balance available in the Electronic Cash Ledger between the return due date and the date of tax payment.
The amount calculated by the system is treated as the minimum interest payable. The taxpayer may increase it where self-assessment shows that a higher amount is due.
Monthly and QRMP Filing Schedules
The filing schedule varies depending on the taxpayer's return frequency.
| Compliance Step | Monthly Filer | QRMP Filer |
|---|---|---|
| GSTR-1 | Filed monthly, normally by the 11th | Filed quarterly, normally by the 13th after the quarter |
| IFF | Not applicable | Optional for months 1 and 2, normally by the 13th |
| GSTR-2B | Generated monthly, normally on the 14th | Not generated for months 1 and 2; a combined quarterly GSTR-2B is normally generated on the 14th of the month following the quarter |
| PMT-06 | Used when funds need to be deposited | Monthly payment for months 1 and 2, normally by the 25th |
| GSTR-3B | Filed monthly, normally by the 20th | Filed quarterly, normally by the 22nd or 24th |
Compliance Step
Monthly Filer
QRMP Filer
Compliance Step
Monthly Filer
QRMP Filer
Compliance Step
Monthly Filer
QRMP Filer
Compliance Step
Monthly Filer
QRMP Filer
Compliance Step
Monthly Filer
QRMP Filer
A taxpayer with aggregate turnover up to ₹5 crore in the preceding financial year may opt for QRMP , subject to the scheme conditions. An eligible taxpayer may also continue to file monthly. Quarterly filing is not automatic merely because turnover is below ₹5 crore.
Example: GST Invoice to Return for One Sale
Suppose a Maharashtra supplier sells goods worth ₹1,00,000 to a GST-registered customer in Delhi on 15 June 2026. Assume that IGST applies at 18%.
| Date | Step | What Happens |
|---|---|---|
| 15 June 2026 | Invoice is created | The sales register records taxable value of ₹1,00,000 and IGST of ₹18,000 |
| By 11 July 2026 | June GSTR-1 is filed | The B2B invoice is reported against the customer's GSTIN |
| Before GSTR-3B | Customer reviews IMS and GSTR-2B | The invoice is matched with the purchase records |
| By 20 July 2026 | Supplier files GSTR-3B | The supplier declares output tax and pays the net liability |
| By 20 July 2026 | Customer files GSTR-3B | The customer claims ITC after checking GSTR-2B and the applicable Section 16 conditions |
Date
Step
What Happens
Date
Step
What Happens
Date
Step
What Happens
Date
Step
What Happens
Date
Step
What Happens
This GST invoice to return example shows the normal monthly flow. Actual filing dates may change if the Government extends a due date.
How BUSY Can Support the GST Filing Process
BUSY accounting software integrates billing, accounting, inventory, GST reports, and reconciliation into a single system. This helps businesses prepare return data from the same records used for everyday invoicing and accounting.
BUSY is trusted by more than 6,00,000 businesses. Businesses can use it to create GST invoices, maintain sales and purchase records, prepare GSTR-1 and GSTR-3B data, reconcile GSTR-2A and GSTR-2B, and manage e-invoices and e-way bills.
Conclusion
GST compliance begins when an invoice is created and recorded correctly, not on the return due date .
Reconciling each stage before moving to the next reduces corrections, buyer disputes, and return mismatches. It also prevents the monthly or quarterly filing cycle from becoming a last-minute exercise.
