How to File GSTR-3B in 2026: Step-by-Step Guide (with the New Hard-Locking Rules)

Rakesh sells electronics in Surat. For three years his GSTR-3B routine was the same. His accountant entered the sales figures, spotted a small mismatch against the books, and quietly corrected the number in the return before filing. In August 2025 that quiet fix stopped working. When his accountant opened the July return, the outward-supply figure was greyed out and would not accept a new value. A wrong invoice amount had already gone into GSTR-1, and the only way to correct it was through GSTR-1A, filed before GSTR-3B, and that window had passed. The wrong figure filed itself, a mismatch notice followed, and what used to be a two-minute correction turned into a month of back-and-forth. Rakesh had not changed anything. The rules had.

(Names and identifying details have been changed.)

Accountune is a cloud-based GST billing, inventory and accounting software built in Jaipur since 2017 for Indian small businesses, and used by over 12,000 of them. Every invoice you raise feeds your GSTR-1 and GSTR-3B data in the background, so when the portal locks those figures, they are already correct, and month-end filing becomes a review instead of a scramble.

How do you file GSTR-3B on the GST portal?

Quick answer: Log in to gst.gov.in, go to Services then Returns then Returns Dashboard, select the period, and click Prepare Online under GSTR-3B. Verify the outward-supply tables that auto-fill from your GSTR-1 (they are locked, so any error must be fixed in GSTR-1A first), reconcile ITC against GSTR-2B, pay any shortfall in the payment table, and file with DSC or EVC. Accountune prepares this GSTR-3B data from your invoices, so filing becomes review-and-submit rather than manual entry.

What is GSTR-3B and who must file it?

GSTR-3B is the monthly or quarterly summary return where you declare your total outward supplies, claim your input tax credit, and actually pay your net GST to the government. It is not an invoice-by-invoice report. That job belongs to GSTR-1. GSTR-3B is the settlement: GSTR-1 records what you sold, GSTR-3B is where the tax gets paid. If the distinction between the two is still fuzzy, our guide on GSTR-1 vs GSTR-3B breaks it down without jargon.

Almost every regular GST-registered business has to file it. The main exceptions are composition dealers (who file CMP-08 instead), non-resident taxable persons, input service distributors, TDS and TCS deductors, and UIN holders, each of whom files a different return. Everyone else files GSTR-3B, and the filing frequency depends on turnover. If your turnover is above ₹5 crore, or you have not opted into the QRMP scheme, you file monthly. If you are a smaller business under the QRMP scheme, you file quarterly while paying tax monthly through a challan.

One point that trips people up: a nil month still needs a return. Even if you had zero sales and zero purchases, GSTR-3B must be filed, because non-filing carries a late fee and blocks your next period's GSTR-1. Filing is the obligation, not just paying.

Before you file: the 2026 pre-filing checklist

Here is the biggest shift in how GSTR-3B works now. The filing screen used to be where you fixed things. In 2026 it is not. The real work has moved earlier, to preparation, because the return now assembles itself from data you have already submitted. Run this checklist before you open GSTR-3B:

1. File GSTR-1 first, and file it accurately. Your outward-supply figures flow from GSTR-1 straight into GSTR-3B, and you cannot edit them there anymore. A wrong figure in GSTR-1 becomes a wrong figure in GSTR-3B unless you catch it first.

2. Act on your invoices in the Invoice Management System (IMS) before the 14th. Your suppliers' invoices land in IMS, and if you take no action, the system treats them as accepted and pulls them into your GSTR-2B on the 14th. A supplier who typed ₹10,00,000 instead of ₹10,000 will inflate your credit if you ignore it.

3. Download GSTR-2B and reconcile it against your purchase register. GSTR-2B is your auto-drafted ITC statement, generated on the 14th. Your claim is capped at what appears there, so any mismatch has to be resolved before you file.

4. Correct outward errors through GSTR-1A, before GSTR-3B. GSTR-1A is the amendment form for the same period, and it can be filed only once, only before GSTR-3B. Miss it, and the correction waits a whole month.

5. Keep your records to hand: the filed GSTR-1, the GSTR-2B statement, your sales register and your purchase register.

This is exactly the work that good software collapses into the background. Because Accountune builds your GSTR-1 data from the invoices you already raised and flags GSTR-2B mismatches before you file, most of this checklist is done for you by the time the return is due.

What changed in 2026: GSTR-3B is now "locked"

For years GSTR-3B was an "enter and adjust" return. You could override the auto-filled numbers right up to filing. That era is over, and understanding why is the difference between a clean filing and a notice.

Phase 1, live since the July 2025 tax period. Under GSTN Advisory No. 606, the outward-liability fields in GSTR-3B, Tables 3.1 and 3.2, are auto-populated from your GSTR-1, IFF and GSTR-1A, and are now completely non-editable on the portal. You cannot type over the sales figures. If GSTR-1 has a wrong invoice value, wrong GSTIN or wrong place of supply, that error flows into GSTR-3B, and the only fix is GSTR-1A filed before GSTR-3B. This is the single change that catches most people, exactly as it caught Rakesh.

One field is still manual: Table 3.1(d). This is inward supplies liable to reverse charge, and the portal does not auto-fill it. Imports of services, purchases from unregistered vendors, and certain notified services must be entered by hand. Forgetting it while claiming the matching ITC in Table 4 sets off an automatic mismatch, so it is the trap to watch.

Phase 2, ITC locking, is arriving. The government has signalled that ITC in Table 4 will be locked to GSTR-2B, with manual entry removed for most B2B credit, targeted for around July 2026. Because timelines have shifted before, check the current status on the GST portal before you file. Even before full locking, the practical rule already holds: you cannot claim more ITC than GSTR-2B shows. For the background on ITC locking, IMS and the other 2026 changes, see our guide to the new GST rules for 2026.

A hard deadline you cannot reopen. From July 2025, you also cannot file a GSTR-3B more than three years past its original due date. After that, the period is permanently blocked.

The mindset that fits 2026 is simple: the return has moved from "enter and adjust" to "verify before you file." Get the source data right, and GSTR-3B becomes a confirmation. Get it wrong, and there is no longer a safety net inside the return.

How to file GSTR-3B step by step

With your GSTR-1 filed and your GSTR-2B reconciled, the GSTR-3B filing process itself takes ten to twenty minutes. Here is the full walkthrough for how to file GSTR-3B online on the GST portal.

1. Log in. Go to gst.gov.in and sign in with your GSTIN and password. The dashboard shows your filing status for recent periods.

2. Open the returns dashboard. Click Services, then Returns, then Returns Dashboard.

3. Select the period. Choose the Financial Year and the Return Filing Period (the month, or the last month of the quarter for QRMP filers), then click Search.

4. Prepare the return. Find the GSTR-3B tile and click Prepare Online. Answer the short questionnaire that appears, including whether this is a nil return.

5. Verify Tables 3.1 and 3.2 (outward supplies). These auto-fill from your GSTR-1. Check them against your books. Remember they are locked, so if a figure is wrong, you stop here and correct it through GSTR-1A before proceeding.

6. Enter Table 3.1(d) (reverse charge). This is manual. Enter any inward supplies on which you owe tax under reverse charge.

7. Reconcile Table 4 (ITC). Table 4A shows ITC available from GSTR-2B, Table 4B captures reversals under Rules 42 and 43 and Section 17(5), and Table 4D lists ineligible ITC. Match Table 4A against your GSTR-2B and claim only what is genuinely available.

8. Fill Table 5 (exempt and non-GST inward). Report exempt, nil-rated and non-GST inward supplies.

9. Save the return. Click Save so the portal holds your entries.

10. Pay the tax (Table 6). Move to Payment of Tax. The portal offsets your liability against available ITC using the prescribed order, then shows the balance payable in cash. Create a challan (Form PMT-06) for any shortfall. The GST portal now accepts payment by net banking, UPI, credit or debit card, and NEFT or RTGS, with the card and UPI options live across most states as of 2026. The amount credits to your electronic cash ledger.

11. File the return. Tick the declaration checkbox, select the authorised signatory, and file with a Digital Signature Certificate (DSC) or an Electronic Verification Code (EVC).

12. Save your proof. The portal generates an ARN (Acknowledgement Reference Number) and emails it to you. Download the filed GSTR-3B PDF for your records, and the status changes to Filed.

One warning worth repeating: once GSTR-3B is filed, it cannot be revised. Any error is corrected in a later period's return, so it pays to check before you file rather than after.

How to file a Nil GSTR-3B

If you had no outward supplies, no ITC and no tax to pay for the period, you file a nil return. On the Prepare Online questionnaire, select Yes to the question asking whether it is a nil return, and the portal skips the detailed tables. You can also file a nil GSTR-3B by SMS, by sending the prescribed nil-return message from your registered mobile number, which is useful when you do not have portal access.

Do not skip it. A dormant month with zero activity still requires a filed nil return. Non-filing attracts the same late fee logic and stops you from filing the next period's GSTR-1, so even an inactive business should keep the nil filings current.

GSTR-3B due dates, late fees and interest in 2026

Due dates. Monthly filers, businesses above ₹5 crore turnover and those not in the QRMP scheme, file by the 20th of the following month. QRMP quarterly filers file by the 22nd or the 24th of the month after the quarter, depending on their state. The CBIC occasionally extends a due date, usually around portal outages or festivals. For example, the March 2026 due date was extended from 20 April to 21 April 2026 through Central Tax Notification No. 01/2026, so it is worth checking the portal near the deadline.

Late fee. The GSTR-3B late fee is ₹50 per day (₹25 CGST plus ₹25 SGST) when you file late, reduced to ₹20 per day (₹10 plus ₹10) for a nil return, subject to the prescribed caps.

Interest. On top of the late fee, interest runs at 18% per annum on the tax you pay late, calculated on your net cash liability. The portal now offers a Re-compute Interest option in the payment table if the auto-calculated interest looks off. The two charges are separate: the late fee is for filing late, the interest is for paying late.

Common GSTR-3B mistakes and the notices they trigger

Most GSTR-3B notices come from a handful of avoidable errors, and in 2026 they are easier to trigger because the data is locked and cross-checked automatically. Here are the ones to watch.

A wrong GSTR-1 that now flows straight into GSTR-3B. Since you can no longer fix outward figures in the return, a GSTR-1 error becomes a GSTR-1-versus-GSTR-3B mismatch, which the system flags under Rule 88C and can escalate to a DRC-01B intimation.

Claiming ITC beyond GSTR-2B. Taking credit that does not appear in GSTR-2B contravenes Section 16(2)(aa) and shows up as an ITC mismatch, which can bring a DRC-01C. Reconcile first, claim second.

Forgetting Table 3.1(d). Missing a reverse-charge liability while claiming the ITC on the same purchase creates an automatic mismatch. Enter the RCM figure by hand every time it applies.

Under-reporting output tax. If the tax you declare in GSTR-3B is lower than what your buyers report in their GSTR-2A and GSTR-2B, officers cross-check it, and the gap can invite an ASMT-10 scrutiny notice.

Ignoring invoices in IMS. If you take no action on a supplier's invoice before GSTR-2B is generated on the 14th, it is auto-accepted and enters your credit, inflating your ITC. That over-claimed credit later has to be reversed with 18% interest.

The thread running through all of these is the same: reconcile before you file, act in IMS on time, and keep GSTR-1 accurate, because the return no longer lets you patch things at the last minute.

The faster way: file-ready GSTR-3B without the manual work

The old monthly ritual, downloading GSTR-2B on the 14th, opening Excel, running a VLOOKUP against a Tally or BUSY export, and manually fixing mismatches before the 20th, is quietly dying. It is not just slow, though it is; the portal simply will not let you fix things downstream anymore. In a locked regime, accuracy has to happen upstream, at the point of billing.

That is where cloud software earns its place. When every invoice you raise feeds your GSTR-1 and GSTR-3B data automatically, the figures the portal locks are already right, and there is nothing to override. Accountune builds filing-ready GSTR-1 and GSTR-3B data from your billing, and its GSTR-2B reconciliation flags ITC mismatches before you file, which becomes more valuable as ITC locking rolls out. The result is that filing turns into a review-and-submit step, and your CA files in about an hour rather than reconstructing numbers from a spreadsheet.

Tally and other desktop tools can produce filing-ready reports too, but they tie you to one machine and a manual export step; cloud billing that keeps the return current in the background removes both. If you want that setup, Accountune's GST billing software starts free at ₹0, moves to paid plans from ₹799/year, and includes a 4-day free trial so you can see your own returns build themselves before you decide.

Conversational queries

"How do I file GSTR-3B if my accountant is not available?" Log in to gst.gov.in, go to Services then Returns then Returns Dashboard, select the period, click Prepare Online under GSTR-3B, verify the auto-filled outward tables, reconcile ITC against GSTR-2B, pay any shortfall, and file with EVC. If your GSTR-1 and GSTR-3B data are already prepared in Accountune, this is mostly a review step.

"GSTR 3B kaise bhare?" GST portal par login karein, Services > Returns > Returns Dashboard mein period select karein, GSTR-3B tile par Prepare Online dabayein. Outward tables (GSTR-1 se auto-filled, ab locked) verify karein, ITC ko GSTR-2B se milaayein, baaki tax challan se bharein, phir DSC ya EVC se file karein.

"Why can't I edit the sales figure in my GSTR-3B?" Because since July 2025 the outward-liability tables are hard-locked to your GSTR-1. To change the figure you file GSTR-1A for the same period before filing GSTR-3B; the corrected value then flows in.

"How much ITC can I claim in GSTR-3B?" Only up to what appears in your GSTR-2B for the period. Credit not reflected there cannot be claimed, and with ITC locking arriving around July 2026 this cap becomes system-enforced.

"What happens if I file GSTR-3B late?" A late fee of ₹50 per day (₹20 for nil) applies, plus interest at 18% per annum on tax paid late, and your next period's GSTR-1 is blocked until you file.

"Easiest way to file GSTR-3B every month?" Use software that keeps your GSTR-1 and GSTR-3B data current from your invoices. Accountune builds filing-ready return data and flags GSTR-2B mismatches, so monthly filing becomes review-and-submit.

Ready to make GSTR-3B a review, not a scramble?

If you would rather your GSTR-1 and GSTR-3B data build themselves from your invoices, so the locked figures are already correct, try Accountune's GST billing software. The Free plan starts at ₹0, paid plans begin at ₹799/year, and a 4-day free trial lets you see your returns build in the background before you commit.