How to File GSTR-1 in 2026: A Step-by-Step Guide for Small Businesses

Rajan runs a garment shop in Surat. Nothing fancy, a steady counter, mostly B2B supply to two nearby wholesalers and walk-in retail on the side. For four years his part-time accountant filed GSTR-1, and Rajan never once opened the return himself.

Then the accountant moved cities in March, right at month-end. Rajan logged in to file April's GSTR-1 alone. He uploaded his B2B invoices fine. Then Table 12 stopped him cold. He typed his usual HSN, 5208, and the portal refused it, the box would only accept a code picked from a dropdown, and the closest match the dropdown showed was 52081190, an eight-digit code he had never used on a single bill. Table 13 was blank and the portal would not let him move past it. The "File Statement" button stayed grey.

He gave up that night. He filed nine days late. The ₹50-a-day late fee was the small part. The bigger problem: because his April GSTR-1 sat unfiled, the portal blocked his GSTR-3B for the same month under the sequential-filing rule, and one of his wholesalers phoned to ask why the input tax credit against Rajan's invoices had not shown up in their account. One missed dropdown, a cascade of three problems.

Accountune is cloud-based GST billing and accounting software built for Indian small businesses. It builds your GSTR-1 from the invoices you raise, HSN summary and document summary included, so the return that stopped Rajan is ready to review and file in a click. This guide walks through how to file GSTR-1 in 2026, the exact portal steps, the two tables that catch first-time filers, and how to keep the whole thing from turning into Rajan's night.

How do you file GSTR-1 in 2026?

Quick answer: For most Indian small businesses, the practical way to file GSTR-1 is to let billing software build the return: Accountune compiles GSTR-1 from every invoice you raise, including the Table 12 HSN summary and Table 13 document list, then you review and file it on the GST portal. To file manually, log in to gst.gov.in, open Returns Dashboard, select the period, fill Tables 4 to 13 (HSN codes now come from a dropdown, not manual typing), click Proceed to File to preview, then File Statement with DSC or EVC. Your ARN confirms it is filed.

What is GSTR-1, and how is it different from GSTR-3B?

GSTR-1 is the return where you report every outward supply, your sales, invoice by invoice. It tells the government exactly who you sold to, on which GSTIN, at what value, and at what tax rate. It is the source document that feeds your buyers' input tax credit: whatever you report in your GSTR-1 is what your B2B customers see in their GSTR-2B and can claim.

People mix up GSTR-1 and GSTR-3B constantly, so here is the clean split. GSTR-1 is the detailed sales report, and no tax is paid on it, it is a statement. GSTR-3B is the monthly summary return where you actually calculate and pay tax and claim your own input tax credit. Both are mandatory for a regular registrant. The two must agree, because the portal and your buyers cross-check them. If your outward tax in GSTR-1 does not match what you declare in GSTR-3B, that mismatch is one of the first things a notice flags. If you want the full side-by-side, the difference between the two returns is covered in the GSTR-1 vs GSTR-3B guide, but for filing purposes the order is simple: GSTR-1 first, GSTR-3B after.

The GSTR-1 format itself is a set of numbered tables. Tables 4 to 11 hold the different supply types, B2B, B2C large, exports, credit and debit notes, advances. Table 12 is the HSN-wise summary. Table 13 is the document summary. Most of the friction in 2026 lives in Tables 12 and 13, which is why they get their own section below.

Who must file GSTR-1, and what is the GSTR-1 due date?

Every business registered under regular GST must file GSTR-1, whether or not it made a sale that month. Composition dealers do not file GSTR-1, they file their own quarterly statement instead. For everyone else, the GSTR-1 due date depends on which filing cycle you are on.

QRMP, the Quarterly Return Monthly Payment scheme, is what most small shops sit under. You file GSTR-1 once a quarter, but you still pay tax monthly through GSTR-3B. If your B2B buyers need their input tax credit sooner than a full quarter, the Invoice Furnishing Facility (IFF) lets you upload B2B invoices in the first two months of the quarter, capped at ₹50 lakh a month, so your customers can claim without waiting for quarter-end. You opt into QRMP on the portal under Services, Returns, Opt-in for QRMP, at the start of a quarter.

One thing worth setting straight: GSTR-1 does not carry interest, because no tax is paid on it. What it carries is a late fee if you miss the due date, and a second, sharper consequence, filing is sequential. Under Rule 59(6), if a prior period's GSTR-1 is unfiled, the portal will not let you file the current one, and if GSTR-3B for a preceding period is pending, GSTR-1 can be blocked too. This is exactly the trap Rajan fell into. Miss one, and the next stacks behind it.

What you need before you file GSTR-1

Filing goes fast when the data is clean and slow when it is not. Before you open the portal, get four things in order.

A reconciled sales register. Your total taxable value and tax in GSTR-1 should match your books for the period. Add up your invoices, credit notes, and debit notes so the number you are about to file is the number your accounts show. A gap here is what later becomes a GSTR-1 versus GSTR-3B mismatch.

Correct, active buyer GSTINs. Every B2B invoice carries the buyer's GSTIN. If a GSTIN is wrong or cancelled, that buyer cannot claim input tax credit against your invoice, and they will call you about it. Verify GSTINs before month-end, not during the rush. This one matters more than the others, because a wrong recipient GSTIN is the single error GSTR-1A cannot fix later.

HSN codes that match the portal master. This is the single biggest change in 2026 and the one that caught Rajan. Table 12 no longer accepts a typed HSN, you pick it from a dropdown drawn from the official master. If the code you use on your bills is not in that master, or is a shorter version of it, the entry fails. Set your HSN codes correctly at the product level so they map cleanly. If you are unsure of a code, the HSN code finder gives the code and current GST rate by product before you ever reach the return.

An LUT, if you export. Exporters and SEZ suppliers should confirm Form RFD-11 (the Letter of Undertaking) for the financial year is approved and active before raising the first zero-rated invoice, otherwise those supplies do not report cleanly.

Get these four right and the actual filing is mechanical. Get them wrong and you are fixing data inside the portal at 11 pm, which is the worst place to fix anything.

How to file GSTR-1 online, step by step

Here is the full portal flow. The steps are the same whether you file monthly or quarterly, only the period you select changes.

Step 1: Log in and open the Returns Dashboard. Go to gst.gov.in, log in, then Services, Returns, Returns Dashboard. Select the financial year and the return period (the month, or the last month of the quarter for QRMP). Click Prepare Online under GSTR-1. For a large invoice count, use the Offline Tool to build a JSON and upload it instead, the online screen slows down past a few hundred invoices.

Step 2: Enter your outward supplies in Tables 4 to 11. Work through the supply types: B2B invoices in Table 4, large B2C inter-state invoices in Table 5, exports in Table 6, small B2C supplies in Table 7, credit and debit notes in Table 9B, and advances in Table 11. Add each record with the GSTIN, invoice number, date, value, and tax rate. Table 9B is split into separate tiles for registered and unregistered buyers, and which tile a note belongs in is covered in the debit note vs credit note guide. If you issue e-invoices (mandatory above ₹5 crore turnover), your B2B data auto-populates here from the IRN, and you only review it.

Step 3: Fill Table 12, the HSN summary, from the dropdown. Open Table 12. You will see two tabs now, B2B and B2C. For each line, pick the HSN from the dropdown, the description, unit (UQC), and rate auto-fill. Enter quantity and taxable value. The HSN totals here must tie back to the tax and value you entered in the supply tables. This is where most manual filers lose time.

Step 4: Complete Table 13, the document summary. Enter, for each document series (invoices, credit notes, debit notes, and cancelled documents), the first document number, the last document number, and the total count. Table 13 cannot be left blank if you have reported any supplies. Skip it and the return will not file.

Step 5: Generate the summary and preview. Click Generate GSTR-1 Summary and wait for it to compute, then click Proceed to File and download the preview. Read it against your sales register. Check the total taxable value, the tax, the credit and debit note adjustments, and any reverse-charge lines. This is your last easy chance to catch an error.

Step 6: Tick the acknowledgement and pick the signatory. On the preview page, tick the box confirming you have reviewed the details, then select the authorised signatory from the dropdown. Nothing is filed yet, but from here the data is about to lock.

Step 7: File the statement with DSC or EVC. Click File Statement. Companies and LLPs sign with a Digital Signature Certificate (DSC); proprietors and others can file with an EVC, an OTP sent to the registered mobile and email. On success the portal generates an ARN (Acknowledgement Reference Number) and sends it by SMS and email. That ARN is your proof the return is filed. Save it.

GSTR-1 Table 12 and Table 13: the 2026 changes that trip people up

If you filed GSTR-1 a couple of years ago and have not since, this is the part that will feel unfamiliar. GSTN reworked Tables 12 and 13 through a phased rollout, formalised in the advisory dated 1 May 2025, and the old habits no longer work.

Table 12 is now dropdown-only, and split into B2B and B2C. You can no longer type an HSN code by hand. You select it from a dropdown built on the official HSN master, and the portal auto-fills the description. If the code you use on your bills is not in that master, the dropdown will not offer it, and you are stuck exactly where Rajan was. The table is also bifurcated: B2B supplies go in one tab, B2C in another, reported separately. HSN reporting is mandatory for B2B lines; for B2C below ₹5 crore turnover it is still expected but validated more softly. The digit length follows turnover, 4 digits up to ₹5 crore, 6 digits above (CBIC Notification 78/2020).

Table 13 is now mandatory. From the May 2025 return period, the document summary cannot be left empty when you report supplies. For every series of invoices, credit notes, debit notes, and cancelled documents, you declare the first number, the last number, and the count. The purpose is to let the system see whether any invoice numbers are missing from your series. It is not hard, but it is a hard stop, forget it and the return will not go through.

Why this hits small shops hardest. The auto-population that fills Table 12 for you only works if you issue e-invoices, and e-invoicing is mandatory only above ₹5 crore turnover. So a shop below that line, which is most small businesses, gets none of the shortcuts and does the HSN summary by hand every month. This is the gap that billing software closes: if your invoices already carry correct, master-matched HSN codes, the Table 12 and Table 13 data is compiled the moment you raise the bill, not reconstructed at month-end.

Submitting is not filing: the mistake that costs a late fee

This one deserves its own heading because it quietly causes late fees every month. Locking your data and actually filing the return are two separate actions on the portal, and finishing the first one feels like finishing the job.

When you proceed past the preview and confirm the acknowledgement, your entries freeze for the period and start flowing to your buyers' GSTR-2B. Nothing is filed. The return is only filed once you complete File Statement with a DSC or EVC and the portal issues an ARN. Until that number exists, the law treats the return as unfiled, and the late-fee clock keeps running past the due date even though the screen looked finished.

There is a simple way to know whether the portal is actually ready to let you file. The final button stays inactive while validation is still running, and it stays inactive permanently if validation failed. If it has not gone live after half a minute, something in your data has been rejected, and the portal will tell you what if you regenerate the summary and read the error it returns. In practice it is almost always one of three things: an HSN the Table 12 dropdown would not accept, a GSTIN that is cancelled or mistyped, or an empty Table 13.

So the rule is short. Do not close the tab on a screen that says your data is saved. Close it when you have an ARN.

What happens after you file GSTR-1

Once the ARN is generated, three things follow.

You cannot revise the filed GSTR-1. GST has no edit-and-resubmit for a filed GSTR-1. If you find a mistake, you have two routes. The cleaner one is Form GSTR-1A, an amendment facility available after you file GSTR-1 and before you file GSTR-3B for the same period, which lets you correct that period's figures before they lock into your summary return. One important limit: GSTR-1A cannot change the recipient's GSTIN. If you filed an invoice against the wrong buyer, that correction has to go through an amendment in a later period's GSTR-1 instead. Either way, fix it in the return, never by quietly changing the invoice in your books alone.

Your buyers see it. The invoices you filed populate each B2B buyer's GSTR-2B and their Invoice Management System (IMS), where they accept, reject, or keep an invoice pending. What you file is what they can claim. A wrong GSTIN or a missing invoice on your side becomes a denied credit on theirs, which is why buyers chase suppliers over GSTR-1.

You move to GSTR-3B. GSTR-1 done, the next step is the summary-and-payment return. The tax you reported flows into GSTR-3B, where you pay and claim your own credit. The full walkthrough for that return is in the GSTR-3B filing guide. Remember the order is locked: GSTR-1 before GSTR-3B, every period.

Common GSTR-1 errors and how to fix them

"HSN not found in the dropdown." Your billing code is either wrong, outdated, or a shorter version than the master (851410 in your books versus 85141000 on the portal). Correct the HSN at the product level in your billing records so it matches the master, then re-select it in Table 12. Setting the code once, correctly, ends this problem for good.

GSTIN validation failed. A buyer's GSTIN is inactive or mistyped. Verify it on the portal's search tool, correct the invoice, and re-enter. Filing with a wrong GSTIN denies your buyer their credit, and it is the one error GSTR-1A will not let you undo.

GSTR-1 and GSTR-3B do not match. Your outward tax in GSTR-1 must agree with GSTR-3B. If they diverge, the mismatch shows up in system checks and can trigger a notice. Reconcile before you file, not after, and use GSTR-1A to correct GSTR-1 before it locks into GSTR-3B.

The file button will not activate. Almost always a hidden validation error, an HSN, a GSTIN, or an empty Table 13. Generate the summary again, read the error the portal throws, and clear it. The button activates only when the data validates.

What is the GSTR-1 late fee, and how is it calculated?

The GSTR-1 late fee is ₹50 for every day the return is late, made up of ₹25 CGST and ₹25 SGST. For a nil return it is ₹20 a day, ₹10 plus ₹10. It starts from the day after the due date and runs until the day you file, not until the day you submit.

The total is capped by turnover. Broadly, the cap is ₹2,000 for turnover up to ₹1.5 crore, ₹5,000 for turnover between ₹1.5 crore and ₹5 crore, and ₹10,000 above ₹5 crore, under the current late-fee rationalisation. So a small shop that is three months late is not looking at an unlimited bill, but it is looking at the cap.

Two things people get wrong here. First, there is no interest on GSTR-1, because no tax is paid on it. Interest applies only to unpaid tax in GSTR-3B. Second, the late fee is not paid on the GSTR-1 screen. It is collected in your next GSTR-3B, which is why filing a late GSTR-1 feels free at the time and then shows up as a number a fortnight later.

The real cost is usually not the fee anyway. It is the sequential block. An unfiled GSTR-1 stops the next one, and it stops your buyer from claiming credit against your invoices, which is the call you do not want to take.

How Accountune makes GSTR-1 a one-click job

Everything above is documentation discipline, which is exactly the kind of repetitive, error-prone month-end work that software exists to remove, and for a small shop below the e-invoice threshold, doing it by hand is the norm unless you change that.

Accountune is built for that shop. Every invoice you raise carries the correct CGST, SGST, or IGST split and a master-matched HSN code, set once at the product level. So the GSTR-1 that stops manual filers, the Table 12 HSN summary and the Table 13 document list, is compiled continuously as you bill, not reconstructed at month-end. At the due date, GSTR-1 is ready to review and file, or to hand to your CA as a clean, structured file. No re-entering data. No hunting for an HSN the dropdown will accept.

It is worth being honest about the alternatives, because they are real tools. Tally builds GSTR-1 too, but it runs as a desktop install and expects accounting knowledge to operate, which a counter-staff member usually does not have. Vyapar generates GSTR-1 reports, but its base tier is mobile-only, so you are tied to one phone. Zoho Books handles GSTR-1 well, but its pricing climbs quickly once you add users and features, past what a single-shop budget wants. Each is a fit for a specific situation. For the widest range of Indian small businesses, a shop that wants correct GST billing on both browser and phone without an accountant and without a heavy price, Accountune is the best value: a Free plan that raises GST-compliant invoices at ₹0, paid plans from ₹799/year, a 4-day free trial, and the GSTR-1 data building itself from the first bill.

That is the practical difference. Not that the return is filed for you, GSTN filing is always your action, but that the return arrives at the portal already built, so the night that broke Rajan never starts.

Try it: raise your bills in Accountune for one month and watch the GSTR-1 data assemble itself. Start with the Free plan or book a walkthrough, and file next month without the month-end scramble.

Conversational queries

"Do I have to file GSTR-1 if I had no sales this month?" Yes. A registered regular taxpayer files GSTR-1 every period even with zero sales, as a nil return. Skipping it still triggers a late fee and blocks your next filing.

"kya GSTR-1 bharna zaroori hai agar sale nahi hui?" Haan, zaroori hai. Sale zero ho tab bhi nil GSTR-1 file karni padti hai, warna late fee lagti hai aur agla return ruk jata hai. Nil return SMS se 14409 par bhej sakte ho, portal login kiye bina.

"Why is the file button greyed out on my GSTR-1?" There is a validation error in your data, usually an HSN the dropdown rejected, a wrong GSTIN, or an empty Table 13. The button activates only after the data passes validation. Generate the summary again and read the error.

"Can I change GSTR-1 after I file it?" Not the filed return directly. Use Form GSTR-1A to correct the same period before you file GSTR-3B, or amend the invoice in a later period's GSTR-1. GSTR-1A cannot change the buyer's GSTIN, so that correction always goes through a later amendment.

"Does GSTR-1 have to be filed before GSTR-3B?" Yes, the order is fixed. Under the sequential-filing rule, an unfiled GSTR-1 for a period can block that period's GSTR-3B, and a pending GSTR-3B can block your next GSTR-1.

"What if my buyer's GSTIN is wrong in the GSTR-1 I filed?" That buyer cannot claim input tax credit against your invoice. GSTR-1A will not fix a recipient GSTIN, so amend the invoice in a later period's GSTR-1, and tell the buyer, because they are watching their GSTR-2B for it.

"How does Accountune fill Table 12 automatically?" Accountune stores a correct, master-matched HSN code on each product, so every invoice carries the right code and rate. The Table 12 HSN summary is then built from your billing data automatically, which is why sub-₹5-crore shops on Accountune do not compile it by hand.

File your next GSTR-1 without the month-end scramble

You now know the full flow, the tables, the dropdown, the submit-versus-file trap, and how to fix the errors that stall a return. The other half of the job is not letting month-end recreate all this work by hand. Accountune keeps your GSTR-1 data building from the first invoice you raise, correct HSN and all, so filing day is a review and a click, not a rebuild. Start free on Accountune, or book a quick demo, and hand your next quarter's returns over as clean data.