GSTR-3B for September 2026: 20, 22 and 24 October Due Dates, ITC Checks & Late-Filing Risks

October 2026 is an important month for GST compliance because businesses must complete their applicable GSTR-3B returns, reconcile input tax credit, verify tax liabilities and ensure that payments are made within the prescribed deadlines. Missing a GST return deadline can result in late fees, interest on delayed tax payments and additional compliance work.

For September 2026, the ordinary GSTR-3B due date for regular monthly filers is 20 October 2026. Eligible taxpayers who have opted for the Quarterly Return Monthly Payment (QRMP) scheme file their July–September 2026 quarterly GSTR-3B by 22 October or 24 October 2026, depending on the principal place of business of the relevant GST registration.

These three dates do not apply interchangeably to every taxpayer. The correct deadline depends on the filing frequency selected for the relevant GSTIN and the applicable provisions of the Central Goods and Services Tax Rules, 2017. Taxpayers should also check for any applicable government extension or special notification before relying on an ordinary due date.

This guide explains the GSTR-3B September 2026 due dates, the difference between monthly filing and QRMP, ITC reconciliation, GSTR-2B checks, reverse-charge liability, late-filing risks, interest calculations and a practical checklist for businesses and accountants.

1. What Is GSTR-3B?

GSTR-3B is a summary GST return through which eligible registered taxpayers report their tax liability, input tax credit and other prescribed information for a tax period. The taxpayer uses the return to declare the applicable tax amounts and discharge the resulting liability according to GST law.

Unlike a detailed sales register, GSTR-3B presents summary information. However, the amounts reported in the return must be supported by appropriate accounting records, sales and purchase invoices, GST statements and other relevant documents.

For example, a business may have sales of ₹10,00,000 during September 2026 and purchases of ₹6,00,000. The GST payable cannot be calculated simply by subtracting the purchase value from the sales value. The business must consider applicable tax rates, eligible input tax credit, blocked credit, reverse-charge transactions, credit notes, debit notes and other relevant adjustments.

Correct preparation of GSTR-3B therefore requires more than entering totals into the GST portal. Businesses should reconcile their underlying transactions and verify that the reported figures reflect the correct tax treatment.

2. GSTR-3B Due Dates for September 2026

The ordinary filing deadline depends on whether the taxpayer files monthly or quarterly under the QRMP scheme.

These are ordinary statutory deadlines. If a competent authority issues an applicable extension, taxpayers should follow the terms and scope of that notification.

A business with multiple GST registrations should verify each GSTIN separately. A company may have registrations in different states and may use different filing frequencies for eligible registrations. The filing category of one GSTIN should not automatically be applied to another.

3. Who Must File GSTR-3B by 20 October 2026?

The ordinary 20 October deadline applies to regular monthly filers reporting their September 2026 tax period. These taxpayers must prepare their September summary return, reconcile the relevant liability and ITC information, pay any amount due and complete filing through the GST portal.

Businesses should begin preparation before the deadline rather than waiting until the final day. This is particularly important for taxpayers with large transaction volumes, multiple branches, substantial ITC claims, reverse-charge transactions or invoices requiring supplier clarification.

Documents to review before monthly filing

• September sales register and outward supply invoices.
• GSTR-1 and applicable amendments.
• Purchase register and supplier invoices.
• September GSTR-2B and relevant supporting statements.
• Credit notes and debit notes.
• Reverse-charge transaction records.
• Electronic credit ledger and electronic cash ledger.
• Earlier-period adjustments and credit reversals.
• Tax payment challans and previous return records.

Reviewing these records helps identify discrepancies before the return is submitted.

4. Who Must File by 22 October 2026?

Taxpayers who have validly opted for QRMP and whose principal place of business falls within the first group specified under Rule 61 of the CGST Rules generally file their July–September 2026 GSTR-3B by the 22nd day of October.

The group includes the following states and union territories under the applicable rule:

• Andhra Pradesh
• Chhattisgarh
• Goa
• Gujarat
• Karnataka
• Kerala
• Madhya Pradesh
• Maharashtra
• Tamil Nadu
• Telangana
• Puducherry
• Andaman and Nicobar Islands
• Lakshadweep
• The union territories specified in the rule, including the applicable Daman and Diu and Dadra and Nagar Haveli references.

For example, a business with a GST registration whose principal place of business is in Tamil Nadu and which has validly opted for QRMP would ordinarily use the 22 October deadline for its July–September quarterly GSTR-3B.

The state classification is based on the relevant GST registration and its principal place of business, not the location of the accountant, consultant, customer or supplier.

5. Who Must File by 24 October 2026?

The second QRMP group generally has the 24th day of the month following the quarter as its ordinary GSTR-3B deadline.

The group includes the following states and union territories under Rule 61:

• Arunachal Pradesh
• Assam
• Bihar
• Chandigarh
• Delhi
• Haryana
• Himachal Pradesh
• Jharkhand
• Manipur
• Meghalaya
• Mizoram
• Nagaland
• Odisha
• Punjab
• Rajasthan
• Sikkim
• Tripura
• Uttar Pradesh
• Uttarakhand
• West Bengal
• The union territories of Jammu and Kashmir and Ladakh, along with Chandigarh as specified under the rule.

For example, a QRMP taxpayer with its principal place of business in Delhi would ordinarily use 24 October 2026 for the July–September quarterly GSTR-3B.

Businesses should confirm their actual filing frequency and applicable date on the GST portal. A taxpayer who files monthly must not assume that the QRMP quarterly deadline applies simply because its turnover is below the scheme's eligibility threshold.

6. What Is the QRMP Scheme?

QRMP stands for Quarterly Return Monthly Payment. It is a GST compliance scheme under which eligible taxpayers file specified returns quarterly while paying tax monthly during the first two months of the quarter, subject to the applicable rules.

The scheme is designed to reduce the frequency of return filing for eligible businesses while preserving monthly tax payment requirements.

Eligibility generally depends on PAN-based aggregate annual turnover, the prescribed turnover threshold, filing status and the applicable option-selection requirements. The commonly applicable threshold is ₹5 crore, subject to the relevant rules and conditions.

Businesses should distinguish eligibility from actual enrolment. A taxpayer does not automatically become a QRMP filer merely because its turnover is below ₹5 crore. The selected filing frequency for the relevant GST registration should be checked on the portal.

Monthly payment under QRMP

QRMP taxpayers generally make payments for the first two months of a quarter through Form GST PMT-06 by the 25th day of the succeeding month, following the applicable fixed-sum or self-assessment method.

For the July–September 2026 quarter, the first two months are July and August. September is the third month of the quarter and is accounted for through the quarterly GSTR-3B and applicable tax payment process.

Therefore, taxpayers should not apply the first-two-month PMT-06 timetable mechanically to September. They should reconcile deposits already made and the final quarter liability before completing the quarterly return.

7. GSTR-3B and GSTR-1: Why Reconciliation Matters

GSTR-1 contains details of outward supplies reported by the taxpayer, while GSTR-3B provides a summary of the tax liability and other information for the applicable period.

These forms serve different purposes, but the relevant figures should be consistent after considering legitimate differences, amendments, credit notes, debit notes, timing matters and other applicable adjustments.

For example, assume a business reports taxable outward supplies of ₹8,00,000 in its books but mistakenly reports only ₹7,50,000 in the relevant GST return data. If the discrepancy is not identified, the corresponding tax liability may also be understated.

The accountant should investigate the difference, identify the underlying invoices and make any permitted correction through the applicable GST procedure.

Outward supply reconciliation checklist

• Match the sales register with GSTR-1.
• Check invoice numbers, dates and taxable values.
• Review applicable GST rates and tax amounts.
• Verify credit notes and debit notes.
• Review amendments to earlier-period invoices.
• Check reverse-charge and other special transaction categories where relevant.
• Compare the liability reported in GSTR-1 with the amount declared in GSTR-3B.
• Document the reasons for any remaining differences.

The GST portal provides comparison reports that help taxpayers identify differences between liability reported in GSTR-1, IFF or GSTR-1A and the amounts reported in GSTR-3B.

8. GSTR-2B and ITC Reconciliation for September 2026

Input tax credit is an important part of GSTR-3B preparation. GSTR-2B is an auto-drafted statement that helps taxpayers review supplier-reported documents and other information relevant to ITC.

However, an invoice appearing in the accounting records does not automatically establish that the associated GST credit is eligible. Taxpayers must satisfy the applicable conditions under GST law and consider restrictions, reversals and relevant time limits.

Before filing the September return, businesses should reconcile their purchase register with GSTR-2B and investigate material differences.

Common ITC mismatch reasons

• Supplier invoices are missing from GSTR-2B.
• The supplier has reported an incorrect GSTIN.
• Invoice numbers or dates differ between records.
• Taxable values or tax amounts do not match.
• Credit notes or debit notes have not been recorded correctly.
• Invoices are reported in a different tax period.
• ITC is restricted under the applicable provisions.
• Credit was reversed in an earlier period but has not been properly tracked.
• Import or reverse-charge credits require separate verification.

Each discrepancy should be investigated individually. The correct treatment depends on the transaction, applicable statutory conditions and available documentation.

9. How to Check ITC Before Filing GSTR-3B

A systematic ITC review helps businesses avoid unsupported claims and identify eligible credit accurately.

Step 1: Download GSTR-2B

Access the GST portal and download the statement for the relevant period. Review the available credit, unavailable credit, amendments and credit notes or debit notes shown in the statement.

Step 2: Compare With the Purchase Register

Match invoice-level information between the accounting system and GSTR-2B. Pay attention to GSTIN, invoice number, date, taxable value and tax amount.

Step 3: Verify ITC Eligibility

Review whether the goods or services were received, whether the transaction is supported by appropriate documents, whether the credit is restricted and whether the other applicable legal conditions have been met.

Step 4: Identify Missing Invoices

Prepare a separate list of invoices recorded in the purchase register but not appearing in the relevant statement. Contact suppliers where appropriate and document the follow-up.

Step 5: Review Reversals and Reclaims

Check earlier credit reversals and confirm that any subsequent reclaim is permitted and supported by evidence. Avoid duplicate or unsupported claims.

Step 6: Reconcile With GSTR-3B

Compare the final eligible credit with the figures reported in the relevant GSTR-3B tables. Review the resulting differences before filing.

10. Important ITC Rules Businesses Should Not Ignore

Input tax credit must be claimed according to the applicable provisions of the CGST Act and Rules. The following areas require particular attention.

Eligibility under Section 16

Section 16 establishes important conditions for claiming ITC. Businesses should verify the applicable requirements, supporting tax documents, receipt of goods or services, supplier-related conditions and prescribed time limits.

Blocked credit under Section 17(5)

Certain categories of input tax credit are blocked or restricted under Section 17(5), subject to specified exceptions. Businesses should not claim credit merely because GST was charged on a purchase.

Credit reversals

Some transactions may require full or partial credit reversal. The reason, amount and relevant period should be documented accurately.

Credit notes and amendments

Credit notes, debit notes and amendments can change the credit position. These documents should be reconciled with the accounting records and relevant GST statements.

Businesses should refer to the current statutory provisions and official guidance rather than relying solely on a software-generated eligible-credit total.

11. Reverse-Charge Mechanism: A Critical Filing Check

Under the reverse-charge mechanism, the recipient is liable to pay GST on specified supplies, subject to the applicable provisions.

Reverse-charge liability should be reviewed separately from ordinary supplier-charged GST. The accountant should identify transactions covered by reverse charge, calculate the applicable liability and ensure that the tax is discharged in the prescribed manner.

Where the taxpayer is eligible for corresponding ITC, the credit must still satisfy the applicable conditions. Payment of reverse-charge tax does not automatically guarantee that every associated amount is available as credit in the same manner or period.

Reverse-charge checklist

• Review expenses and transactions that may attract reverse charge.
• Verify the nature of the supply and applicable GST treatment.
• Calculate the tax liability correctly.
• Check the appropriate reporting period.
• Verify tax payment through the prescribed method.
• Determine ITC eligibility separately.
• Reconcile reverse-charge liability and credit with available GST statements.

Ignoring reverse-charge transactions can result in underreported liability even when the ordinary sales and purchase figures appear correct.

12. GST Payment and Electronic Ledgers

Before filing GSTR-3B, businesses should review their electronic cash ledger, electronic credit ledger and electronic liability register, as applicable.

The electronic credit ledger generally reflects eligible credit available for utilisation under GST rules, while the electronic cash ledger records cash deposits available for payment of tax and other permitted amounts.

Not every liability can be paid using ITC. The applicable utilisation rules, tax heads and restrictions must be considered, and certain liabilities, including reverse-charge tax, generally require payment in cash under the applicable framework.

Businesses should ensure that sufficient funds are available and that the tax liability is correctly discharged before completing the return filing process.

13. Late-Filing Risks for GSTR-3B

Missing the applicable GSTR-3B deadline can create financial and operational consequences. The precise amount depends on the taxpayer's circumstances, the return type, the applicable statutory provisions and any relevant notifications or concessions.

Late fee

Section 47 of the CGST Act provides for late fees for delayed furnishing of specified returns, subject to the applicable provisions, caps, notifications and concessions. The relevant state or union territory GST law may also apply.

The amount should be checked against the applicable legal rules and the portal-generated calculation. Businesses should not assume that every taxpayer has the same maximum late fee.

Interest on delayed tax payment

Interest under Section 50 may apply when tax is paid late or in other circumstances specified by law. The applicable calculation depends on the nature of the liability, the delay period, the statutory rate and relevant rules.

For delayed returns involving tax payable, the treatment of interest may depend on the portion of liability paid through the electronic cash ledger and the applicable statutory conditions. The calculation should not be confused with the late fee for filing a return after its due date.

Additional compliance work

Delayed filing can also complicate subsequent return preparation, reconciliation, tax planning and responses to system-generated communications. Businesses may need to spend additional time reviewing earlier-period data and correcting accumulated discrepancies.

14. Illustrative Late-Filing Cost Calculation

Consider a hypothetical taxpayer who files a taxable GSTR-3B late and has outstanding tax liability. The total financial impact may involve separate late-fee and interest components.

For illustration, assume that an applicable interest rate of 18% per annum applies to a qualifying delayed tax payment. If the relevant amount on which interest is payable is ₹1,00,000 and the qualifying delay is 10 days, a simple illustration is:

Interest = ₹1,00,000 × 18% × 10 ÷ 365

Illustrative interest = approximately ₹493.15

This example is only an arithmetic illustration. The actual amount subject to interest, the applicable start and end dates, the statutory conditions, the effect of cash-ledger balances and any relevant exceptions must be established before calculating the taxpayer's actual liability.

Late fee is a separate component and should be calculated under the applicable legal provisions. Therefore, the illustrative interest amount above should not be treated as the complete cost of filing late.

15. GST Notices and ITC Mismatch Risks

Differences between reported liability and tax paid, or between ITC claimed and credit available in relevant GST statements, may lead to system-generated communications or other compliance action.

The GST portal provides comparison reports for liability declared in GSTR-1, IFF or GSTR-1A against GSTR-3B, and for ITC claimed in GSTR-3B against credit available in GSTR-2A or GSTR-2B.

Specified mismatch procedures may involve forms such as DRC-01B or DRC-01C, depending on the nature of the discrepancy and the applicable rules.

A mismatch communication should be examined carefully. It should not automatically be treated as a final adjudicated demand, but it should not be ignored either.

How to respond to a mismatch

• Identify the tax period and GSTIN involved.
• Download the relevant return and comparison reports.
• Identify the specific liability or credit difference.
• Reconcile the difference with accounting records and invoices.
• Determine whether a correction, payment or explanation is required.
• Prepare supporting documents and a clear reconciliation statement.
• Follow the prescribed response procedure and applicable deadline.

Businesses should seek professional guidance when a mismatch involves material amounts, disputed ITC eligibility, repeated supplier errors or complex legal questions.

16. September 2026 GSTR-3B Filing Checklist

The following checklist can help accountants and business owners review the return before filing.

Sales and output tax

• Reconcile the sales register with GSTR-1.
• Review outward tax liability by applicable tax head.
• Check amendments, credit notes and debit notes.
• Confirm that the correct liability is reported in GSTR-3B.

Purchases and input tax credit

• Download and review GSTR-2B.
• Reconcile supplier invoices with the purchase register.
• Review missing and duplicate invoices.
• Check blocked or restricted credit.
• Verify credit reversals and permitted reclaims.
• Review import-related credit and supporting records where applicable.

Reverse charge and other liabilities

• Identify applicable reverse-charge transactions.
• Verify the tax calculation and reporting period.
• Confirm the prescribed payment treatment.
• Check other applicable liabilities and adjustments.

Payment and filing

• Review the electronic cash ledger.
• Review the electronic credit ledger.
• Confirm that tax and other payable amounts are correctly discharged.
• Review late fee or interest, if applicable.
• Complete the return filing process.
• Download and retain the filed return and acknowledgement.

17. Common Mistakes to Avoid While Filing GSTR-3B

Even experienced accounting teams can make errors when return preparation is rushed. The following mistakes should be avoided.

Using the wrong due date

Monthly filers and QRMP taxpayers have different return periods and deadlines. Confirm the filing frequency for each GSTIN before preparing the return.

Claiming credit without reviewing eligibility

GSTR-2B is an important reconciliation tool, but credit must also satisfy the applicable statutory conditions.

Ignoring reverse-charge liability

Reverse-charge transactions should be identified and reported separately where required.

Failing to reconcile GSTR-1 with GSTR-3B

Differences between outward supply reporting and the summary return should be investigated and addressed using the permitted procedure.

Forgetting earlier-period adjustments

Credit reversals, reclaims, amendments and previous-period tax differences should be reviewed before finalising the current return.

Waiting until the last minute

Last-minute filing increases the risk of incorrect entries, payment problems and missed deadlines. Early preparation provides time to resolve discrepancies.

18. How Businesses Can Improve Their GST Compliance Process

Businesses can reduce repetitive errors by establishing a standard monthly or quarterly GST review process. The process should assign clear responsibilities for invoice entry, reconciliation, tax calculation, review and filing.

For small businesses, a structured spreadsheet and regular review may be sufficient. Larger businesses may benefit from accounting software or GST reconciliation tools that can identify missing invoices, duplicate records, incorrect GSTINs and differences in tax amounts.

Recommended internal controls

• Maintain accurate customer and supplier master data.
• Record invoices promptly and consistently.
• Review GSTR-2B as part of the regular reconciliation cycle.
• Maintain a list of unresolved discrepancies.
• Assign responsibility for supplier follow-up.
• Document credit reversals and reclaims.
• Use a reviewer or approval process before filing.
• Retain filed returns, challans and reconciliation reports.

These controls can help businesses maintain a reliable compliance record and reduce the risk of avoidable errors.

19. GST Return Filing Support for Businesses

GST return filing involves more than submitting a form on the portal. Businesses may need assistance with bookkeeping, reconciliation, ITC eligibility, reverse-charge calculations, payment verification and responses to mismatch communications.

Professional support may be useful for proprietorships, partnership firms, LLPs, private limited companies, retailers, manufacturers, traders, service providers and other registered taxpayers with recurring GST compliance responsibilities.

A structured compliance service can help businesses organise their records, identify discrepancies before filing and maintain appropriate documentation. However, the taxpayer should ensure that all figures and supporting records are accurate and that final filing decisions comply with the applicable GST provisions.

20. Frequently Asked Questions About September 2026 GSTR-3B

1. What is the GSTR-3B due date for September 2026?

The ordinary due date is 20 October 2026 for regular monthly filers. Eligible QRMP taxpayers file their July–September 2026 quarterly GSTR-3B by 22 October or 24 October 2026, depending on the state group specified under Rule 61.

2. Are 20, 22 and 24 October all applicable to every taxpayer?

No. These dates apply to different filing categories. Monthly filers ordinarily use 20 October for September, while QRMP taxpayers use 22 or 24 October for the July–September quarter, depending on the relevant state group.

3. What is the GSTR-3B due date for Tamil Nadu taxpayers under QRMP?

Eligible QRMP taxpayers whose principal place of business is in Tamil Nadu ordinarily have 22 October 2026 as the due date for the July–September 2026 quarterly GSTR-3B, subject to any applicable extension.

4. What is the GSTR-3B due date for Delhi taxpayers under QRMP?

Eligible QRMP taxpayers whose principal place of business is in Delhi ordinarily have 24 October 2026 as the due date for the July–September 2026 quarterly GSTR-3B, subject to any applicable extension.

5. What is the QRMP scheme?

QRMP stands for Quarterly Return Monthly Payment. Eligible taxpayers file specified returns quarterly while making tax payments for the first two months of the quarter according to the applicable rules.

6. Can I claim all ITC shown in my purchase register?

No. Credit must satisfy the applicable GST eligibility conditions. The taxpayer should reconcile purchase records with GSTR-2B, verify supporting documents and review restrictions before claiming ITC.

7. Is GSTR-2B reconciliation mandatory for accurate ITC reporting?

GSTR-2B is an important source for reviewing supplier-reported documents and identifying ITC differences. Taxpayers should reconcile it with their books and independently verify statutory eligibility.

8. What happens if GSTR-3B is filed late?

Late filing can attract applicable late fees and may create interest liability where tax is paid late. The exact amount depends on the circumstances, relevant provisions and any applicable concessions or notifications.

9. Is late fee the same as interest?

No. Late fee relates to delayed filing of the prescribed return, while interest may apply to delayed tax payments or other circumstances specified by law. They must be evaluated separately.

10. What should I do if GSTR-1 and GSTR-3B do not match?

Identify the difference using the relevant comparison reports, investigate the underlying invoices and determine whether a permitted correction or other action is necessary. Retain supporting documentation for the resolution.

11. Do QRMP taxpayers need to pay tax monthly?

Yes, QRMP generally involves monthly payment for the first two months of a quarter under the applicable procedure. The third month's liability is handled through the quarterly return and associated payment process.

12. Should I wait until the due date to prepare GSTR-3B?

No. Businesses should reconcile sales, purchases, ITC, reverse-charge liability and cash-ledger balances before the filing deadline to allow time to correct errors and resolve missing information.

21. Conclusion

GSTR-3B compliance for September 2026 requires taxpayers to identify the correct filing frequency, observe the applicable deadline and verify the accuracy of tax liability and input tax credit.

The ordinary deadline is 20 October 2026 for monthly filers, while eligible QRMP taxpayers filing for July–September 2026 generally use 22 October or 24 October, depending on the principal place of business of the registration.

Before filing, businesses should reconcile GSTR-1 with GSTR-3B, compare purchase records with GSTR-2B, verify ITC eligibility, review reverse-charge liability and confirm that tax payments are correctly discharged. These checks can reduce avoidable errors and help businesses respond more effectively to GST mismatch communications.

Late fees, interest and other compliance consequences depend on the applicable legal provisions and taxpayer-specific facts. Businesses should not assume that every delayed return or mismatch carries the same financial consequence.

By preparing early, maintaining accurate records and following a consistent reconciliation process, businesses can complete their GST return filing more efficiently and maintain better control over their tax compliance responsibilities.