The two returns are filed by the same person in the same month, so they are easy to mix up. They answer different questions and they are read by different people. GSTR-1 is read by your customers, because it becomes part of their GSTR-2B. GSTR-3B is read by the tax department, because it is where the tax is actually declared and paid. This guide sets them side by side and explains the mismatch between them in plain terms.
The difference at a glance
| Point | GSTR-1 | GSTR-3B |
|---|---|---|
| What it is | Monthly or quarterly statement of outward supplies | Simplified summary return to declare liability and discharge it |
| Level of detail | Invoice-level details of supplies to registered persons, credit and debit notes, exports, summary state-level details for unregistered persons, advances, amendments, HSN summary | Summary tables. GSTN says there is no invoice matching in it |
| Who files | Normal and casual registered taxpayers making outward supplies. Composition taxpayers are not required to file it | All normal and casual taxpayers |
| Nil periods | Must be filed even with no business activity | Mandatory even with no business in the period |
| Due date, monthly filer | 11th of the next month | 20th of the next month |
| Due date, quarterly filer | 13th of the month after the quarter | 22nd or 24th of the month after the quarter, as notified for the State or Union Territory |
| Who relies on it | Your customers: it feeds their GSTR-2B | The department: it carries the tax you declare and pay |
| Can it be changed? | Invoices can be modified or deleted until it is filed. After that, through amendments or GSTR-1A | A filed GSTR-3B cannot be revised. Adjustments go into a later period’s return |
| ITC | Not applicable: it reports supplies you made | Table 4 declares your ITC, pre-filled from GSTR-2B |
The GSTN GSTR-1 guide and the GSTR-3B guide are the sources for every row. Due dates can be extended by notification, and GSTN says so on both pages, so confirm the current date when it matters.
How the two returns connect
GSTR-3B is built partly from GSTR-1. GSTN says Table 3.1(a), (b), (c) and (e) and Table 3.2 are auto-drafted in GSTR-3B from GSTR-1/1A. The system-generated GSTR-3B is generated after GSTR-1/1A is filed or GSTR-2B is generated, and its values are not final: the taxpayer can edit them. Table 4, the ITC section, comes from the other side, from GSTR-2B. Table 4 is the part you reconcile against GSTR-2B.
If you have already saved data in GSTR-3B before your GSTR-1/1A is filed, GSTN says the liability details will not be auto-populated in Tables 3.1(a), (b), (c), (e) and 3.2. The system-generated PDF still carries the complete data, and hovering over a cell shows both the system value and the value you entered. That is one common way for a gap to arise before anyone has made a real mistake.
The correction routes differ too. For GSTR-1, a taxpayer can use GSTR-1A to amend or add a record of the same tax period after filing GSTR-1 and before filing GSTR-3B. For invoices of the previous financial year, GSTN says rectification in GSTR-1 is not allowed after 30 November of the following financial year. GSTR-3B has no such window; it is simply not revisable once filed.
The dates in one month
For the September 2026 tax period, a monthly filer works to these dates. A quarterly filer working on July to September 2026 files GSTR-1 by 13 October 2026 and GSTR-3B by 22 or 24 October 2026, depending on the State or Union Territory.
GSTR-2B is generated on the 14th of the month for monthly filers, so the supplier’s GSTR-1 deadline falls three days before your reference statement exists. What a GSTR-1 filed after the 14th does to your 2B is covered in the freeze-date guide. The 14th-to-20th timeline and the generation timeline guide cover the buyer’s side of the calendar.
What a GSTR-1 vs GSTR-3B mismatch means
The word “mismatch” covers three different situations. Only the first can lead to the notice most people fear.
1. GSTR-1 shows more tax than GSTR-3B
This is the case Rule 88C covers. It was inserted by notification 26/2022-CT dated 26 December 2022, and it says that where the tax payable per GSTR-1 (as amended in GSTR-1A, if any) or the invoice furnishing facility exceeds the tax payable per GSTR-3B, by such amount and such percentage as may be recommended by the Council, the registered person is intimated in Part A of Form GST DRC-01B. The intimation directs the person to do one of two things within seven days.
- Pay the differential tax liability, along with interest under Section 50, through Form GST DRC-03; or
- Explain the difference on the common portal.
If the amount stays unpaid and no explanation is furnished, or the explanation is not found acceptable by the proper officer, the amount is recoverable under Section 79. We do not quote the amount and percentage that trigger the intimation, because Rule 88C leaves them to the Council’s recommendation and we have not verified the current figures. Check the latest GSTN advisory for them.
2. GSTR-3B shows more tax than GSTR-1
GSTN’s comparison report shows the shortfall or excess for the period and the cumulative shortfall or excess for the financial year. It highlights in red the values for which the tax liability in GSTR-1 is more than the tax liability in GSTR-3B; the pages we checked do not describe a red flag for the opposite direction. An excess in GSTR-3B cannot be fixed by revising the return, because a filed GSTR-3B cannot be revised. GSTN’s text points to adjustment while filing the return for a subsequent period. Ask your CA how to treat the excess before you do it.
3. A gap with an ordinary cause
Not every difference is an error. GSTN’s comparison compares Table 3.1(a) of GSTR-3B with several GSTR-1 tables together, so a gap can come from the way items are reported rather than from missed sales.
- Credit notes and downward amendments. GSTN says negative values from GSTR-1/1A, which may arise due to credit notes and downward amendment of outward supplies, are not considered in the GSTR-3B table, and the system shows zero.
- Amendments and advances. The comparison includes GSTR-1 Tables 9 and 10 (amendments to earlier periods) and Table 11 (advances received or adjusted), in addition to Tables 4A, 5, 6C and 7, so these can move the figure.
- Saved before GSTR-1. As above, data saved in GSTR-3B before GSTR-1 was filed is not overwritten by auto-population.
- Reverse charge, exports and SEZ supplies. These are compared in their own reports, not in the “other than export and reverse charge” report, so do not add them into that comparison by hand.
You can see the comparison yourself on the portal under Services → Returns → Tax liabilities and ITC comparison, after selecting the financial year and clicking Search. The report is generated on a near real-time basis from your filed GSTR-1 and GSTR-3B. GSTN also says it can be used as a reference to declare liability in GSTR-3B once GSTR-1 is filed for that period.
Do not mix this up with DRC-01C. Rule 88C is about outward tax: GSTR-1 against GSTR-3B. The intimation for ITC in GSTR-3B above ITC in GSTR-2B is Form DRC-01C, a different rule and a different return pair. See the DRC-01C reply guide.
Worked example: a supplier whose GSTR-3B is short
A fabric trader in Surat files GSTR-1 for the September 2026 tax period on 10 October 2026, before the 11th. The comparison below uses the GSTR-1 tables GSTN names for Table 3.1(a). The amounts are tax, not invoice value.
| GSTR-1 table | What it reports | Tax |
|---|---|---|
| 4A | Supplies to registered persons, other than reverse charge | ₹4,10,000 |
| 7 | Supplies to unregistered persons, net of credit and debit notes | ₹50,000 |
| 9 | Upward amendment of an earlier invoice | ₹20,000 |
| Total per GSTR-1 | ₹4,80,000 | |
| 3.1(a) | Declared in GSTR-3B filed on 20 October 2026 | ₹4,20,000 |
| Difference | GSTR-1 higher than GSTR-3B | ₹60,000 |
The arithmetic: ₹4,10,000 + ₹50,000 + ₹20,000 = ₹4,80,000, and ₹4,80,000 − ₹4,20,000 = ₹60,000. The trader prepared GSTR-3B from an ERP summary that was run before ₹40,000 of late invoices were booked, and it never picked up the ₹20,000 amendment. The two causes add up: ₹40,000 + ₹20,000 = ₹60,000.
What happens next depends on whether the gap crosses the Council’s amount and percentage. If it does, an intimation in Part A of DRC-01B arrives and the trader has seven days to pay the ₹60,000 with interest under Section 50 through DRC-03, or to explain. If it does not, the comparison report still shows the shortfall for the period and cumulatively for the year, and the trader should still correct it in the next period’s GSTR-3B, because the filed one cannot be revised. Rule 88C requires interest under Section 50 on the amount paid through DRC-03; work out the figure with your CA, since we have not verified the rate that applies to this case.
Notice what does not happen. The trader’s customers still see every one of the ₹4,10,000 of invoices in their GSTR-2B, because GSTR-2B is built from GSTR-1, not from GSTR-3B. Their ITC is not reduced by the supplier’s short GSTR-3B. Their risk is the one in Section 16(2)(c): credit requires that the tax charged has actually been paid to the Government, and GSTR-2B does not check that.
If your supplier’s two returns do not agree
As a buyer you see only your 2B, which reflects the supplier’s GSTR-1. You do not see whether their GSTR-3B matches. What you can control is how you handle the exposure.
- Supplier has not filed GSTR-1: the invoice is not in your 2B and credit is blocked until it appears. The steps are in supplier not filing GSTR-1.
- Supplier filed GSTR-1 but payment is in doubt: keep it on a hold list and decide the vendor payment policy, as in the payment hold SOP.
- Your own claim above 2B: that is the DRC-01C problem, and the rule that creates it is the one in how GSTR-2B decides the ITC you can claim in GSTR-3B.
For how GSTR-2B differs from GSTR-3B as a document, see GSTR-2B vs GSTR-3B.
A three-comparison routine each month
- Books against GSTR-1 before you file it. Every sales invoice in the ERP should be in the statement, including credit notes and amendments.
- GSTR-1 against GSTR-3B before you pay. Look at the pre-filled Table 3.1 and use the portal’s comparison report after filing to see any shortfall.
- GSTR-2B against your purchase register before you claim. This is the one a reconciliation tool does for you.
Related guides
- GSTR-1 Filing Date: monthly, QRMP and IFF Due Dates 2026
- GSTR-3B October 2026 return deadlines and due dates
- GSTR-1 details: how to check and verify your outward supplies
- GSTR-1 vs GSTR-2B mismatch: causes, investigation and fixes
Frequently asked questions
What is the main difference between GSTR-1 and GSTR-3B?
GSTR-1 is the statement of outward supplies, with the details of what you sold, including invoice-level details of supplies to registered persons. GSTR-3B is a simplified summary return in which you declare the GST liability for the period and discharge it. GSTR-1 feeds your customers' GSTR-2B, and it pre-fills the outward-supply tables of your GSTR-3B.
What are the due dates of GSTR-1 and GSTR-3B?
For monthly filers, GSTR-1 is due on the 11th of the next month and GSTR-3B on the 20th. For quarterly filers, GSTR-1 is due on the 13th of the month after the quarter and GSTR-3B on the 22nd or 24th, as notified for the State or Union Territory. The Government can extend these dates by notification, so check the current notification.
What happens if the tax in GSTR-1 is more than the tax in GSTR-3B?
Under Rule 88C, if the tax per GSTR-1 exceeds the tax per GSTR-3B by the amount and percentage recommended by the Council, the system intimates the difference in Part A of Form GST DRC-01B. You must pay the difference with interest under section 50 through Form DRC-03, or explain it, within seven days.
If my supplier's GSTR-1 and GSTR-3B do not match, does my GSTR-2B change?
No. GSTR-2B is built from what suppliers declare in their GSTR-1/1A, not from their GSTR-3B. But Section 16(2)(c) still requires that the tax charged has actually been paid to the Government, and GSTR-2B does not check that for you.
Check the purchase side of the month
Drop the month’s GSTR-2B (Excel or JSON) and your purchase register into gstr2bmatch.in. The report puts each invoice in a bucket: matched, value mismatch, in books but missing from 2B, in 2B but not in books, with IMS Pending flagged separately, and totals the ITC at risk in rupees. It does not compare your GSTR-1 with your GSTR-3B; use the portal’s comparison report for that. Your GSTR-2B and purchase register files are read in your browser and never uploaded to any server.
Last checked: 1 October 2026. Sources: GSTN GSTR-1 user guide and FAQ, GSTN GSTR-3B user guide and FAQ, GSTN FAQ on comparison of liability declared and ITC claimed, CGST Rules, Rule 88C, GSTN GSTR-1A FAQ, GSTN return view guide (2B generation), CGST Act, Section 16.