Top 10 Mistakes in GSTR-3B That Trigger GST Notices

If you've ever received a GST scrutiny notice and had no idea what you did wrong, you're in large company. Most GSTR-3B mistakes that trigger notices aren't fraud. They're reconciliation gaps, wrong table entries, credits claimed a month early. The GST portal doesn't care about intent. It runs automated comparisons every cycle and flags what doesn't match.

If you're new to GST compliance, understanding these mistakes early can also help you avoid problems after GST registration. 

Here are the 10 that show up most often.

1. GSTR-1 and GSTR-3B turnover don't match

This is the single biggest notice trigger in 2026, and it's been that way for two years running.

Your GSTR-1 reports invoice-level sales. GSTR-3B reports the tax you actually paid. The portal reconciles both every month. If your GSTR-1 shows taxable supply of ₹40 lakh but GSTR-3B shows tax calculated on ₹34 lakh, the system doesn't ask questions first. A Rule 88C notice fires automatically if the gap crosses a threshold. For larger differences, an ASMT-10 under Section 61 follows.

The tricky part is that from July 2025, outward liability in GSTR-3B is hard-locked. Tables 3.1 and 3.2 now pull directly from your GSTR-1 and cannot be manually edited. Earlier, people would adjust the GSTR-3B figure to "correct" a GSTR-1 mistake. That route is gone. If GSTR-1 has a wrong figure, you fix it through GSTR-1A before submitting GSTR-3B. No other way exists now.

Practically, what this means: file GSTR-1 first, check the auto-populated figures carefully, correct via GSTR-1A if needed, then file GSTR-3B.

2. ITC claimed that isn't in GSTR-2B

Second most common. And now, with portal validations tightening since April 2026, also the one that blocks your return mid-filing.

GSTR-2B is generated on the 14th of each month, based on invoices your suppliers filed up to the 13th. Supplier filed on the 15th? Their invoice is not in your GSTR-2B for that month. It will appear next month. If you go ahead and claim ITC on it this month because the invoice is sitting in your books, the portal fires a DRC-01C notice within days. That notice gives you 7 days to either pay the difference or explain it.

Phase 2 of hard-locking, expected from July 2026, will take this further. Table 4A of GSTR-3B (ITC claims) will be locked to GSTR-2B figures. If your claim exceeds GSTR-2B, the portal will block submission entirely. Several practitioners reported this blocking behavior already from April 2026 onwards.

The habit to build: reconcile your purchase register against GSTR-2B before filing, not after. Anything not in GSTR-2B stays out of the claim for that month.

3. ITC on purchases that are blocked under Section 17(5)

Section 17(5) of CGST Act lists a specific set of purchases where ITC simply cannot be claimed. Doesn't matter how legitimate the purchase is. Car insurance for your fleet? Blocked (unless you're in the business of selling cars or insurance). Staff food and beverages? Blocked unless it's a statutory obligation under labour law. Construction materials for your own building? Blocked.

The full list includes motor vehicles (most situations), food, beverages, health services, cosmetic surgery, club memberships, works contract for immovable property construction, and goods used for personal consumption. Businesses claim ITC on these routinely, often because the accountant just processes every invoice without filtering. The officer scrutinising returns knows exactly where to look.

Go through your purchase register once and filter everything against this list before finalising Table 4A. It takes 20 minutes and prevents a notice that takes 20 days to resolve.

4. RCM liability missing from Table 3.1(d)

This is the one that quietly catches a lot of small businesses.

Reverse Charge Mechanism means the buyer pays GST instead of the seller, in certain categories. These include purchases from unregistered vendors in specified categories, import of services, freight from a Goods Transport Agency, legal services from advocates, and some others notified by CBIC.

Table 3.1(d) in GSTR-3B is where you report this RCM liability as outward tax. It is NOT auto-populated. It never has been. So if you're not manually computing and entering it, that row sits at zero.

Now here's the trap. Many businesses claim RCM ITC in Table 4A(3) correctly, but forget to report the corresponding RCM liability in 3.1(d). The RCM ledger on the portal then shows a negative balance, and since December 2025, GSTN's hard validation will block your GSTR-3B from being submitted when that ledger is negative.

Pay RCM liability in cash first. Then claim the ITC. Both in the same period if possible.

5. Incorrect taxable turnover reporting

Not the same as the GSTR-1 mismatch point above. This is about what the broader data ecosystem says about your business versus what your return shows.

The department can see your e-way bill data. They can access AIS (Annual Information Statement) from Income Tax, which pulls bank credits, TDS deducted on your receipts, and payment information from buyers. If your e-way bills suggest ₹80 lakh of goods movement but your GSTR-3B shows ₹60 lakh turnover, that gap raises a question the officer will formally ask.

Similarly, if you have exempt and nil-rated supplies mixed into the taxable supply row, or non-GST supplies shown in the wrong table, the total turnover reconciliation breaks down.

Run a monthly check: total from your sales register, against GSTR-1, against e-way bill report, against bank credits for that month. If those four numbers don't broadly agree, figure out why before filing.

Most Common GSTR-3B Mismatch Notices

6. Not reversing ITC when supplier goes unpaid beyond 180 days

Rule 37 of CGST Rules requires ITC reversal when you haven't paid your supplier within 180 days of the invoice date. You can reclaim it once you do pay, but the reversal is mandatory first.

This gets forgotten constantly. Invoice comes in, ITC claimed in month 1, payment gets delayed due to cash flow, 180 days pass, and the reversal never happens. The ITC Reclaim Ledger on the portal now tracks this. GSTN advisory from December 2025 made it clear: negative balance in this ledger = GSTR-3B filing blocked.

Track payment dates against invoices. Day 150 is a good point to check what's still outstanding and whether any are approaching the 180-day mark.

7. Rule 42 and Rule 43 reversals skipped entirely

If your business makes both taxable and exempt supplies, you can't claim full ITC on inputs used for both. Rule 42 covers general inputs and input services. Rule 43 covers capital goods. The proportion of ITC to reverse depends on your exempt turnover ratio.

Small businesses with minor exempt supplies often skip this entirely, reasoning that the amount will be small. The officer doesn't share that reasoning. During scrutiny, they compute the reversal and raise a demand for the entire unclaimed amount plus interest at 18% per year.

Compute this quarterly. Report in Table 4B(1) of GSTR-3B. Even if the reversal amount works out to ₹500, do it. The practice matters more than the number.

8. Wrong sequence of ITC utilisation

GST law prescribes a specific order for how ITC must be used to pay tax liability. IGST credit goes first against IGST liability, then against CGST, then against SGST. CGST credit can only offset CGST and IGST. SGST credit can only offset SGST and IGST. You cannot use CGST credit to pay SGST or vice versa.

If ITC is applied in the wrong sequence, the tax calculation breaks. What looks like a fully paid return to you looks like a short payment to the portal. The mismatch triggers a notice.

This particular error is more common when someone manually edits the payment breakup on the GSTR-3B payment page. Stick to the sequence the portal suggests unless you have a specific reason not to.

9. ITC claimed after Section 16(4) deadline

ITC for any financial year must be claimed by the earlier of two dates: November 30th of the next financial year, or the date of filing GSTR-9 for that year. After that, the credit is permanently lost. There's no provision to reclaim it, no workaround, no refund.

With hard-locking in place, this has become a harder wall. Businesses that were slow to reconcile during FY 2025-26 are now finding old ITC blocked at the portal level, not just legally time-barred.

By August each year, run a full ITC audit for the previous financial year. Anything unclaimed needs to be filed before November 30th. Waiting until the last month is how ₹3-4 lakh credits get permanently lost because a single reconciliation was delayed.

10. Consecutive late filing

Everyone knows late filing means ₹50 per day in fees for returns with tax liability, ₹20 per day for nil returns. That's not the real risk anymore.

Miss GSTR-3B for two consecutive months and the portal now blocks your future return filing and e-way bill generation. That means you can't move goods legally. For trading businesses, that's effectively being shut down.

There's also a 36-month hard stop introduced in 2026. If a return remains unfiled for 3 years, the filing window closes permanently on the portal. You can't correct the record, even if you want to. Several businesses discovered this the hard way while trying to file old pending returns.

File on time, even if the numbers aren't perfect. A timely filed return with a small error is always easier to fix than one that never got filed.

How GSTR-3B hard-locking changes things from 2025-26 onwards

 

FAQs

What is the most common GSTR-3B mistake that triggers a GST notice?

GSTR-1 aur GSTR-3B ka turnover gap. You showed ₹40 lakh in GSTR-1 but paid tax on ₹34 lakh in GSTR-3B. Portal catches it same cycle. Small gap log sochte hain chalta hai — nahi chalta. Rule 88C ya ASMT-10 aa jaata hai.

Can I revise GSTR-3B after filing?

No. Once submitted, it's done. Wrong number in outward supply? Fix via GSTR-1A next month. Short tax? Pay through DRC-03 with interest. No edit button exists anywhere.

What's the difference between DRC-01C and ASMT-10?

DRC-01C is system-generated, only for ITC exceeding GSTR-2B. 7 days to reply. ASMT-10 comes from an officer, covers broader issues — turnover gap, e-way bill mismatch, AIS discrepancy. 30 days to reply. One is automated, other is manual.

Can excess ITC be reversed later?

Yes, but interest runs from the original claim date at 18% per annum. People do the reversal and forget the interest part. That's what the follow-up notice asks about.

What happens when GSTR-3B filing gets blocked?

Since December 2025, negative balance in ITC Reclaim Ledger or RCM Ledger blocks submission. Pay RCM liability in cash or reverse excess ITC first. After ledger turns non-negative, filing goes through.

Does late filing trigger a notice?

Late fees yes, scrutiny notice not always. But two consecutive months missed and portal blocks all future returns plus e-way bill generation. After 36 months, that filing window closes permanently - no catching up.

What is Section 17(5)?

List of purchases where ITC is blocked. Cars, food, club memberships, health services, own building construction. Many accountants don't filter invoices against this list. Officers check it first during scrutiny. Pull these out of Table 4A before filing.

How to avoid GST notices from GSTR-3B?

Match GSTR-1 and GSTR-3B turnover before submitting. Reconcile purchase register with GSTR-2B. Enter RCM liability in Table 3.1(d) before claiming RCM ITC. Remove Section 17(5) credits. File on time. That's it - most notices come from skipping these steps in a filing rush.

Conclusion

GSTR-3B mistakes are not always difficult to avoid. In many cases, the problem starts with a small mismatch, an incorrect ITC claim, a missed RCM entry, or a return filed without checking the figures properly.

Before filing, it is a good idea to match GSTR-1 with GSTR-3B, check ITC against GSTR-2B, review RCM entries, remove blocked ITC under Section 17(5), and check pending ITC reversals. Also, make sure the return is filed on time.

GST return filing is becoming more closely linked with the data already available on the portal. So, checking the figures before submitting the return can help avoid unnecessary GST notices, interest, ITC reversals, and further queries from the tax department.

A simple check before filing can save a lot of work later. Review the numbers, fix any mismatch, and then submit your GSTR-3B.

 

Author Bio:

Chanchal Gabrani is a GST and business compliance specialist at FreeGST.co, helping businesses, startups, and MSMEs understand GST registration, returns, and compliance through practical, up-to-date guidance.