GSTR-1 is the return where you tell the government about your sales. It is built entirely from your outward-supply invoices — so if your invoicing is clean, filing GSTR-1 is mostly a matter of organising that data into the right boxes. Here’s how it works, step by step.
What GSTR-1 is (and why it matters)
GSTR-1 reports all your outward supplies for a tax period. It matters beyond your own compliance: the data you file flows into your buyers’ records and determines the input tax credit they can claim. Errors or omissions in your GSTR-1 directly hurt your customers’ ITC — which is why accuracy is critical.
Due dates
| Filing frequency | Due date |
|---|---|
| Monthly | 11th of the following month |
| Quarterly (QRMP) | 13th of the month after the quarter |
The sections of GSTR-1
GSTR-1 is organised into tables, each fed from a category of your invoices:
- B2B — supplies to registered persons, reported invoice-wise (with buyer GSTIN)
- B2CL — large inter-state B2C invoices above the threshold, invoice-wise
- B2CS — all other B2C, reported as consolidated rate-wise totals
- CDNR / CDNUR — credit and debit notes (to registered / unregistered persons)
- Exports — zero-rated supplies, with shipping bill details
- Advances — advances received and their adjustment (mainly services)
- HSN Summary — HSN/SAC-wise summary of what you supplied
- Documents issued — the range of invoice/challan serial numbers used
Step-by-step: preparing and filing GSTR-1
Step 1 — Gather the period’s invoices
Collect all outward-supply documents for the month/quarter: tax invoices, export invoices, credit/debit notes, and advance receipt vouchers. Completeness here prevents mismatches later.
Step 2 — Classify each invoice
Sort every document into its GSTR-1 bucket:
- Registered buyer → B2B
- Unregistered, inter-state, above threshold → B2CL
- Other unregistered → B2CS
- Returns/adjustments → CDNR/CDNUR
- Exports → export table
Step 3 — Verify the key data
For each B2B invoice, double-check the buyer’s GSTIN, invoice number, date, taxable value and tax. A wrong GSTIN is the single most common cause of your customer’s ITC being blocked.
Step 4 — Build the summaries
Total your B2CS sales rate-wise, and compile the HSN summary at the required digit level (4 digits up to ₹5 crore, 6 digits above). Note the document series issued.
Step 5 — Enter or upload to the portal
On the GST portal, either key the data into each table or upload a JSON prepared from your accounting/invoicing tool or the government offline utility. Uploading from clean data is far faster and less error-prone than manual entry.
Step 6 — Reconcile and submit
Cross-check totals against your books, resolve any mismatches, then submit and file GSTR-1 (with DSC or EVC). After filing, the data becomes visible to your buyers.
The role of clean invoicing
Notice that every step above depends on your invoices being accurate and well-classified in the first place. Correct GSTINs, right HSN/SAC codes, proper B2B/B2C tagging and a clean invoice series turn GSTR-1 from a monthly headache into a quick export-and-map exercise.
Common mistakes
- Wrong buyer GSTIN in B2B — blocks the customer’s ITC.
- Mis-tagging B2CL vs B2CS — wrong reporting of large inter-state sales.
- Missing credit notes — overstates your liability.
- Incomplete HSN summary at the wrong digit level.
- Filing late — attracts late fees and delays buyers’ ITC.
The bottom line
GSTR-1 is simply your sales, organised into the return’s tables — B2B invoice-wise, B2C in summary, plus notes, exports and the HSN summary. Gather the period’s invoices, classify them, verify the GSTINs, build the summaries, upload and reconcile. The cleaner your invoicing, the easier the filing.
Start with accurate, well-structured invoices — create them free with the RaiseBill Bill Maker.