10 Common GST Mistakes New Businesses Make and How to Avoid Them

Registration and Setup Mistakes

1. Assuming the Same Registration Threshold Applies to Every Business

Many new business owners assume that GST registration becomes compulsory only after turnover crosses ₹40 lakh. This limit is not available to every business.

Notification 10/2019-Central Tax provides an exemption from registration up to ₹40 lakh for eligible persons engaged exclusively in supplying goods. The benefit is subject to conditions, state-based exclusions, and restrictions on specified supplies. Businesses providing services generally follow the applicable ₹20 lakh or ₹10 lakh threshold, unless compulsory registration or another exemption applies.

Aggregate turnover is also calculated on an all-India, Permanent Account Number basis for the financial year. It includes taxable supplies, exempt supplies, exports, and inter-state supplies made under the same PAN.

Inter-state supply does not always make registration compulsory. For example, Notification 10/2017-Integrated Tax provides threshold-based relief to eligible inter-state suppliers of taxable services. Notification 34/2023-Central Tax also allows eligible unregistered suppliers of goods to sell through e-commerce operators when its conditions are met.

How to avoid the mistake: Check the nature of your supplies, state of operation, aggregate turnover, sales channels, and compulsory registration provisions before applying a single threshold.

2. Choosing the Composition Scheme Only Because It Appears Simpler

The composition scheme can reduce routine compliance for eligible small businesses, but lower compliance does not automatically make it the right choice. A composition taxpayer generally cannot collect GST separately from customers, claim input tax credit, or make inter-state outward supplies. The business must issue a bill of supply instead of a tax invoice.

The general turnover limit is ₹1.5 crore, subject to lower limits and exclusions for specified states and activities. A separate scheme under Section 10(2A) of the CGST Act is available to eligible service providers and mixed suppliers whose preceding financial-year turnover does not exceed ₹50 lakh.

The scheme may suit a small business selling mainly to consumers. It may be commercially unsuitable for a business whose registered customers expect a tax invoice and want to claim input tax credit .

How to avoid the mistake: Compare the scheme based on your customers, purchase-credit position, turnover, and inter-state sales plans, not only on the number of returns to be filed.

3. Leaving Registration Details Incomplete

Receiving a Goods and Services Tax Identification Number does not complete every registration requirement. Under Rule 10A of the CGST Rules, bank-account details must generally be furnished within 30 days from the grant of registration or before filing GSTR-1 or using the Invoice Furnishing Facility, whichever is earlier. Missing or invalid bank details may lead to portal restrictions or suspension proceedings.

Rule 18 also requires the registration certificate to be displayed prominently and the GSTIN to be shown on the name board at every registered place of business. Changes to the address, authorised signatory, contact details, bank account, or additional place of business should be updated through the prescribed amendment process.

How to avoid the mistake: Review the registration profile immediately after approval and update it whenever an important business detail changes.

Invoice and Tax Mistakes

4. Issuing Invoices With Missing Details or the Wrong Tax Head

A tax invoice must contain the particulars prescribed under Rule 46 of the CGST Rules. These include the invoice number and date, supplier and recipient details, GSTIN where applicable, HSN or SAC, description, taxable value, GST rate, tax amount, and place of supply where required.

A business may use more than one invoice series, but each series should remain consecutive and unique for the financial year. Duplicate numbers, reused numbers, and unexplained gaps can create problems during return reconciliation.

Another common error is deciding between IGST and CGST plus SGST only from the customer’s state. The correct tax head depends on the supplier’s location and the applicable place-of-supply provisions under the IGST Act. Special rules may apply to bill-to and ship-to transactions , installation, immovable property, transport, events, and other services.

If CGST and SGST are wrongly paid instead of IGST, or the reverse, the correct tax generally has to be paid, and the tax deposited under the wrong head must be claimed as a refund. Sections 77 of the CGST Act and 19 of the IGST Act provide relief from interest on the correct tax when the error is limited to an incorrect inter-state or intra-state classification.

How to avoid the mistake: Verify the customer’s GSTIN, transaction movement, place of supply, invoice series, and tax head before the invoice is issued.

5. Copying an HSN, SAC, or GST Rate From an Old Invoice

A product description used by a supplier or competitor is not proof of the correct HSN code or GST rate for your transaction. Classification can depend on the product’s material, composition, packaging, use, and exact wording in the applicable rate notification.

A 40% rate was added to the Invoice Registration Portal’s tax-rate master in September 2025, while the existing rate options remained available. However, the presence of a rate in a portal or accounting-software master does not mean that it applies to every product. The correct GST rate must be determined from the relevant rate notification, HSN or SAC classification, and transaction details. 

How to avoid the mistake: Confirm the HSN or SAC and rate from the latest notification before creating the item master. Recheck the master whenever a product, packaging format, or rate notification changes.

Purchase and Input Tax Credit Mistakes

6. Claiming ITC Only Because an Invoice Appears in GSTR-2B

GSTR-2B is an important reconciliation statement, but it does not automatically approve input tax credit. Under Section 16 of the CGST Act , the recipient must satisfy several conditions. These include holding a valid tax invoice or prescribed document, receiving the goods or services, ensuring that supplier-reported details have been communicated, filing the return, and meeting the other payment and documentation requirements.

The Invoice Management System allows recipients to accept, reject, or keep eligible records pending. These actions affect GSTR-2B preparation, but accepting a document does not override blocked-credit rules or prove that the goods or services were received.

For example, a supplier invoice may appear in GSTR-2B even though the purchase was for personal use or relates to a blocked category. Such credit may still be ineligible.

How to avoid the mistake: Match GSTR-2B with the purchase register, goods-receipt records, expense purpose, supplier details, and the legal ITC conditions before making a claim.

7. Claiming Blocked Credit or Missing the ITC Deadline

Section 17(5) restricts input tax credit on specified inward supplies , subject to stated exceptions. These commonly include certain motor vehicles, food and beverages, club memberships, personal consumption, gifts, free samples, works-contract services, and construction of immovable property.

Recording an expense in the business books does not automatically make its GST eligible for credit. The nature of the expense, its use, the recipient, and any statutory exception must be checked.

Section 16 (4) also sets the normal deadline for claiming ITC . Credit relating to an invoice or debit note for a financial year must generally be claimed by 30 November following that financial year or the date of filing the relevant annual return, whichever is earlier.

Interest should not be applied mechanically to every reversal. Under Section 50(3) , interest applies when ITC has been wrongly availed and utilised.

How to avoid the mistake: Review blocked-credit categories separately and identify missing invoices well before the November deadline.

8. Ignoring Reverse Charge or Applying It to Every Unregistered Purchase

Reverse charge does not apply merely because a supplier is unregistered. Sections 9 (3) and 9(4) apply only to notified supplies and notified classes of recipients.

Transactions that may require review include specified goods transport agency services, legal services received from an advocate, sponsorship, director services supplied to a company, and import of services. Each category has its own conditions and exceptions.

Where reverse charge applies, the liability is generally paid through the electronic cash ledger . Eligible ITC may then be claimed after the tax is paid and the normal credit conditions are satisfied.

A self-invoice under Section 31(3)(f) is relevant when the supplier is unregistered, and the registered recipient is liable to pay tax under the applicable reverse-charge provision. It is not required in every reverse-charge transaction.

How to avoid the mistake: Maintain a separate review of freight, legal fees, director payments, imports, and other expenses that may fall under a reverse-charge notification.

Return Filing Mistakes

9. Filing GSTR-1 Without Reconciling the Sales Register

One of the most important GST filing mistakes is treating GSTR-1 and GSTR-3B as separate exercises. From the July 2025 tax period, outward tax liability auto-populated in GSTR-3B from GSTR-1, GSTR-1A, or IFF became non-editable. If an outward-supply figure is incorrect, the taxpayer generally needs to correct it through GSTR-1A before filing GSTR-3B for that period.

This makes pre-filing reconciliation essential. Invoice values, debit notes, credit notes , advances, amendments, exports, e-invoices, cancelled documents, GST rates, and tax heads should be checked before GSTR-1 is submitted.

How to avoid the mistake: Finalise and reconcile the sales register before filing GSTR-1. Do not rely on making an unrestricted manual adjustment later in GSTR-3B.

10. Ignoring Nil Returns or Leaving Old Returns Pending

An active registered person may still be required to file a return even when there were no sales, purchases, tax liability, or input tax credit during the period. A nil return should not be skipped merely because the business had no activity.

Pending returns can also block subsequent filings because specified GST returns must be filed sequentially. Delayed filing may attract late fees, while interest may apply where tax remains unpaid.

A more serious restriction applies to old returns. The Finance Act, 2023 introduced a three-year filing limit for returns covered by Sections 37, 39, 44 and 52. The provision took effect on 1 October 2023, and GSTN began enforcing the portal restriction from the November 2025 tax period.

Once three years have passed from the original due date, the covered return can no longer be filed through the portal. The restriction applies to forms including GSTR-1 or IFF, GSTR-1A, GSTR-3B, GSTR-4, GSTR-5, GSTR-5A, GSTR-6, GSTR-7, GSTR-8 and GSTR-9 or GSTR-9C.

How to avoid the mistake: Review the return dashboard regularly and file pending returns well before they reach the three-year deadline.

Worked Example: How GST Mistakes Affect Quarterly Cash Flow

Consider Sharma Electricals, a newly registered distributor that identifies three errors while closing its quarterly books.

First, it reported an intra-state sale of ₹4,00,000 as an inter-state sale and paid ₹72,000 as IGST at 18%. It must pay the correct ₹36,000 CGST and ₹36,000 SGST and separately claim a refund of the ₹72,000 paid under the wrong head. The amount is recoverable, but it remains blocked until the refund is processed. Section 77 provides interest relief where the error is limited to treating an intra-state supply as inter-state, or the reverse.

Second, an old item master applied 12% GST instead of the correct 18% to taxable sales of ₹3,00,000. This creates a tax shortfall of ₹18,000, excluding any applicable interest.

Third, purchase ITC of ₹25,000 is not reflected in GSTR-2B. The business should defer the claim until the prescribed conditions are met, increasing its immediate cash payment by another ₹25,000. The three errors create an immediate quarterly cash-flow impact of ₹1,15,000:

The full ₹1,15,000 should not be described as a permanent compliance cost. Of this amount, ₹72,000 is recoverable through the refund process, ₹25,000 is deferred ITC, and ₹18,000 is the actual tax shortfall before applicable interest. The example shows how separate invoicing, rate-master and reconciliation errors can combine into a significant working-capital problem.

Monthly Process to Prevent GST Mistakes

A reliable GST process begins with clean books rather than last-minute portal work. Close the sales and purchase registers before preparing returns, review changes made to tax-rate and party masters, reconcile purchases with GSTR-2B, and resolve missing or disputed records before claiming ITC.

Accounting software can help control invoice numbering, tax rates, customer GSTINs, sales reconciliation, and return data. However, the system will still follow the information entered into it. Incorrect classification or master data can therefore reproduce GST errors across many invoices.

BUSY can help businesses maintain GST invoices, reconcile transaction data, and prepare return information in one system. Questions involving classification, place of supply , composition eligibility, blocked credit, or reverse charge should still be reviewed by a qualified tax professional.

Conclusion

GST errors are easier to prevent before an invoice or return is filed. New businesses should treat registration, invoicing, classification, input tax credit, reverse charge, and return filing as connected parts of one compliance process.

Clear records and timely reviews make it easier to identify errors before they lead to additional tax, interest, credit reversal or delayed filings.