GST Registration, Returns & Compliance: Everything You Need to Know

The Goods and Services Tax has fundamentally changed how businesses operate in India. Since its rollout on 1 July 2017, GST has unified a fragmented indirect tax structure into a single framework -- but it has also introduced a compliance burden that catches many businesses off guard. Late filings, ITC mismatches, and incorrect HSN codes are among the most common issues we see in our practice, and most of them are entirely avoidable with the right understanding.

This guide is written from the perspective of a practising Chartered Accountant who has handled GST registration, filing, and audit work for hundreds of clients across industries. Whether you are a new business owner trying to understand your obligations or an existing taxpayer looking to tighten your compliance, this article covers the essential ground.

1. When Is GST Registration Mandatory?

GST registration is not optional once you cross certain thresholds or fall into specific categories. The rules are straightforward, but the consequences of non-compliance are severe -- including penalties, interest on tax liability, and denial of Input Tax Credit to your buyers.

Turnover-Based Thresholds

• Supply of goods: Registration is mandatory when aggregate turnover exceeds Rs. 40 lakhs in a financial year (Rs. 20 lakhs for special category states such as the North-Eastern states, Himachal Pradesh, Uttarakhand, and others).
• Supply of services: The threshold is Rs. 20 lakhs (Rs. 10 lakhs for special category states).

"Aggregate turnover" includes all taxable supplies, exempt supplies, exports, and inter-state supplies of a person having the same PAN, computed on an all-India basis. This is a critical point -- many businesses mistakenly look at turnover of a single state or a single unit.

Mandatory Registration Regardless of Turnover

Certain categories require GST registration irrespective of turnover:

• Inter-state supply: If you supply goods or services across state borders, registration is compulsory from the first rupee. There is no threshold exemption for inter-state supply.
• E-commerce operators and sellers: If you sell through e-commerce platforms like Amazon, Flipkart, or Swiggy, you must register regardless of turnover. The e-commerce operator (TCS collector) also needs separate registration.
• Casual taxable persons: Anyone making occasional taxable supplies in a state where they have no fixed place of business.
• Non-resident taxable persons: Foreign entities supplying goods or services in India.
• Persons liable to pay tax under reverse charge mechanism.
• Agents of a supplier and Input Service Distributors.

A common mistake we see: businesses making only intra-state supplies assume they do not need registration when they start selling on Amazon. The moment you list on an e-commerce platform, the turnover threshold no longer applies.

2. Types of GST Registration

Regular Registration

This is the standard registration for most businesses. You file monthly or quarterly returns, charge GST to customers, and claim Input Tax Credit on your purchases. There are no restrictions on the nature of supply or turnover ceiling (beyond the minimum threshold to register). Most businesses operating B2B or with inter-state operations should opt for regular registration.

Composition Scheme

The Composition Scheme is designed for small taxpayers who want simplified compliance. Key features:

• Eligibility: Aggregate turnover must not exceed Rs. 1.5 crore (Rs. 75 lakhs for special category states).
• Tax rate: Manufacturers pay 1% of turnover, restaurants pay 5%, and other suppliers pay 1%.
• Filing: One quarterly return (CMP-08) and one annual return (GSTR-4) instead of monthly filings.
• Restrictions: You cannot collect tax from customers (the tax is paid out of pocket), you cannot claim ITC, you cannot make inter-state supplies, and you cannot supply through e-commerce platforms.

The Composition Scheme works well for local businesses with B2C operations -- think neighbourhood retailers, small restaurants, and local manufacturers. It is unsuitable for anyone in the B2B chain where buyers need ITC.

Input Service Distributor (ISD)

An ISD is a registration specifically for offices that receive tax invoices for input services used by multiple branches or units. The ISD distributes the Input Tax Credit proportionally to each branch using ISD invoices. This is common in large organisations with a centralised procurement or head office model. From April 2025, ISD registration has become mandatory for distributing ITC of input services procured from third parties to distinct persons.

3. GSTR Forms: What to File and When

GST compliance revolves around a set of returns, each serving a distinct purpose. Missing a filing deadline does not just attract late fees -- it blocks your ability to file subsequent returns and can freeze your ITC claims.

GSTR-1: Outward Supply Statement

• Purpose: Details of all outward supplies (sales) made during the period.
• Frequency: Monthly (by the 11th of the following month) for taxpayers with turnover above Rs. 5 crore. Quarterly for those under the QRMP scheme.
• Why it matters: Your GSTR-1 data flows into your buyers' GSTR-2A/2B. If you file late or file with errors, your buyers cannot claim ITC on those purchases. This directly impacts your business relationships.

GSTR-3B: Summary Return

• Purpose: Summary of outward supplies, ITC claimed, and net tax payable.
• Frequency: Monthly (by the 20th of the following month) or quarterly under QRMP.
• Why it matters: This is where you actually pay the tax. GSTR-3B is the payment return. Late filing attracts a late fee of Rs. 50 per day (Rs. 20 for nil returns) plus 18% interest on the outstanding tax amount.

GSTR-9: Annual Return

• Purpose: Consolidated annual summary of all monthly/quarterly returns filed during the year.
• Due date: 31st December of the following financial year.
• Who must file: All regular taxpayers. Composition dealers, casual taxable persons, ISDs, and non-resident taxable persons are exempt.

GSTR-9C: Reconciliation Statement

• Purpose: Reconciliation between the annual return (GSTR-9) and the audited financial statements.
• Who must file: Taxpayers with aggregate turnover exceeding Rs. 5 crore.
• Key point: GSTR-9C is now a self-certified reconciliation statement. It no longer requires CA certification (this changed from FY 2020-21 onwards), but we strongly recommend having a CA review it before submission. The reconciliation exercise often uncovers discrepancies that, if left unaddressed, can trigger notices.

4. QRMP Scheme for Small Taxpayers

The Quarterly Return Monthly Payment (QRMP) scheme is available to taxpayers with aggregate turnover up to Rs. 5 crore. Under this scheme:

• GSTR-1 and GSTR-3B are filed quarterly instead of monthly.
• Tax must still be paid monthly using the PMT-06 challan by the 25th of the following month.
• You can use either the fixed sum method (pay 35% of the tax paid in the last quarter) or the self-assessment method (calculate actual liability for the month).
• B2B invoice data can be uploaded using the Invoice Furnishing Facility (IFF) in the first two months of the quarter, so your buyers get timely ITC.

The QRMP scheme significantly reduces the filing burden for small businesses. However, the monthly payment requirement is frequently overlooked. We have seen clients incur interest charges simply because they assumed quarterly filing meant quarterly payment.

5. Input Tax Credit: Eligibility, Blocked Credits & Reversal

Input Tax Credit is the backbone of GST -- it ensures tax is levied only on value addition at each stage. However, ITC is also the area where the maximum disputes and notices arise.

Eligibility Conditions

• You must hold a valid tax invoice or debit note.
• You must have actually received the goods or services.
• The tax charged must have been paid to the government by the supplier (reflected in your GSTR-2B).
• You must have filed your return for the relevant period.
• ITC must be claimed by the due date of the September return of the following financial year, or the date of filing the annual return -- whichever is earlier.

Blocked Credits (Section 17(5))

Certain purchases are permanently ineligible for ITC, regardless of their business use:

• Motor vehicles and conveyances (with exceptions for specified businesses).
• Food and beverages, outdoor catering, health services, cosmetic and plastic surgery (unless used for further supply of the same category or as part of a taxable composite/mixed supply).
• Membership of clubs, health and fitness centres.
• Travel benefits for employees on vacation (LTC).
• Works contract services for construction of immovable property (except plant and machinery).
• Goods or services used for personal consumption.
• Goods lost, stolen, destroyed, written off, or disposed of by way of gift or free samples.
• Tax paid under the Composition Scheme.

ITC Reversal Rules

ITC already claimed must be reversed in certain situations:

• Non-payment to supplier: If you do not pay the invoice amount (including GST) within 180 days, the ITC must be reversed. It can be re-claimed upon payment.
• Exempt and taxable supplies: If inputs are used for both taxable and exempt supplies, ITC must be proportionally reversed under Rule 42 (for inputs and input services) and Rule 43 (for capital goods).
• GSTR-2B mismatch: ITC claimed in GSTR-3B cannot exceed the ITC available in GSTR-2B by more than a prescribed percentage (currently limited to amounts appearing in GSTR-2B plus 5% of the eligible credit from GSTR-2B). Any excess claim triggers auto-populated differences in the return.

6. E-Invoicing Requirements

E-invoicing (electronic invoicing through the Invoice Registration Portal) is now mandatory for businesses with aggregate turnover exceeding Rs. 5 crore in any financial year from FY 2017-18 onwards. The threshold has been progressively reduced from Rs. 500 crore when it was first introduced, and further reductions are expected.

How E-Invoicing Works

• You generate the invoice in your billing software in a prescribed JSON format.
• The invoice is uploaded to the Invoice Registration Portal (IRP), which validates it and assigns an Invoice Reference Number (IRN) and a QR code.
• The signed invoice with IRN is returned to your system and shared with the buyer.
• The data auto-populates in GSTR-1, reducing manual filing effort.

Key Compliance Points

• E-invoicing applies to B2B supplies, exports, and supplies to SEZ units/developers.
• An invoice without a valid IRN is not considered a valid tax invoice -- meaning the buyer cannot claim ITC on it.
• Cancellation of an e-invoice on the IRP must be done within 24 hours. After that, you must issue a credit note.
• Certain categories (banking, insurance, GTA, passenger transport) are exempt from e-invoicing.

7. E-Way Bill Requirements

An E-Way Bill (EWB) must be generated on the E-Way Bill portal before the movement of goods in the following cases:

• Inter-state movement: Mandatory for consignment value exceeding Rs. 50,000.
• Intra-state movement: Thresholds vary by state; many states have adopted the Rs. 50,000 limit, but some have lower thresholds or additional requirements.

Practical Considerations

• The E-Way Bill is valid for a specified distance and duration. For example, up to 200 km validity is one day, and each additional 200 km adds one day.
• The EWB can be generated by the supplier, recipient, or transporter.
• Part-B of the EWB (vehicle number) must be updated before actual movement. Goods intercepted without a valid EWB attract a penalty equal to the tax amount or Rs. 10,000 -- whichever is higher.
• E-Way Bills are now integrated with e-invoicing. If you generate an e-invoice for a B2B supply involving movement of goods, Part-A of the EWB is auto-populated from the e-invoice data.

8. GST Audit and Reconciliation

While the mandatory GST audit by a CA (under Section 35(5)) was removed from FY 2020-21, the reconciliation exercise remains critically important. The GSTR-9 and GSTR-9C together form the annual compliance checkpoint, and the department uses this data extensively for scrutiny and assessment proceedings.

Key Reconciliation Areas

• Turnover reconciliation: Match turnover reported in GSTR-1/3B with the books of accounts and audited financials. Differences arise from advances, credit notes, round-off adjustments, and classification of exempt vs. non-GST supplies.
• ITC reconciliation: Match ITC claimed in GSTR-3B with GSTR-2B (auto-populated from supplier returns) and the books of accounts. Any difference must be explained or reversed.
• Tax payment reconciliation: Verify that tax paid through cash ledger and ITC ledger matches the liability declared in returns.
• HSN-wise summary: GSTR-9 requires HSN-wise reporting of outward and inward supplies. Errors here are a common trigger for notices.

In our experience, the annual reconciliation exercise almost always uncovers discrepancies -- usually small ones that can be corrected through DRC-03 payments or amendments. It is far better to find and fix these proactively than to wait for a departmental notice.

9. Common Compliance Mistakes

Having handled GST compliance for hundreds of businesses, we see certain mistakes repeated consistently:

Late Filing and Penalties

GSTR-3B filed even one day late attracts a late fee (Rs. 50 per day, capped at Rs. 10,000 per return for returns with tax liability; Rs. 20 per day, capped at Rs. 500 for nil returns) plus 18% per annum interest on the outstanding tax amount. Many small businesses underestimate how quickly these penalties accumulate across multiple return periods.

ITC Mismatch Between GSTR-3B and GSTR-2B

This is the single most common trigger for GST notices. If the ITC you claim in GSTR-3B exceeds what is reflected in your GSTR-2B (based on your suppliers' GSTR-1 filings), you will receive an automated intimation under DRC-01C. The fix requires either reversing the excess ITC with interest or getting your supplier to file or correct their returns.

Incorrect HSN Codes

Using the wrong HSN (Harmonized System of Nomenclature) code can result in incorrect tax rate application, rejection of ITC for your buyers, and complications during assessment. From FY 2021-22 onwards, HSN reporting at 4-digit or 6-digit level is mandatory depending on turnover. Businesses with turnover above Rs. 5 crore must use 6-digit HSN codes.

Not Reconciling Books with Returns Monthly

Many businesses file returns based on rough figures and plan to "reconcile later." By the time the annual return is due, the discrepancies have compounded and become difficult to trace. Monthly reconciliation takes a fraction of the effort that year-end correction requires.

Ignoring Reverse Charge Mechanism

Certain supplies require the recipient (not the supplier) to pay GST under the reverse charge mechanism. Common examples include legal services from individual advocates, transportation by a GTA (Goods Transport Agency), and services from unregistered persons in notified categories. Failure to pay RCM liability results in the ITC being denied along with interest and penalty.

10. How to Handle GST Notices and Assessments

Receiving a GST notice is not uncommon. The department has become increasingly data-driven, and automated mismatches trigger notices on a large scale. Here is how to approach them:

Types of Common Notices

• ASMT-10: Scrutiny notice seeking clarification on discrepancies found in returns.
• DRC-01: Show Cause Notice for demand of tax not paid, short paid, or erroneously refunded.
• DRC-01C: Intimation for ITC mismatch between GSTR-2B and GSTR-3B.
• CMP-05: Show Cause Notice for denial of Composition Scheme.
• REG-17: Show Cause Notice for cancellation of registration.

Response Strategy

• Do not ignore any notice. Every GST notice has a response deadline, and non-response is treated as acceptance of the demand.
• Start by downloading and reading the notice carefully on the GST portal. Identify the exact nature of the discrepancy.
• Gather supporting documents -- invoices, bank statements, ledger extracts, GSTR-2B data, and reconciliation workings.
• Draft a detailed, point-by-point reply addressing each allegation. Reference specific invoice numbers, return periods, and amounts.
• If the demand is partly valid, consider paying the admitted amount through DRC-03 to reduce the disputed amount and demonstrate good faith.
• For complex notices or large demands, engage a qualified CA or tax professional before responding.

11. Practical Tips from Handling Hundreds of GST Clients

These are lessons drawn from real-world practice, not textbook advice:

• Reconcile GSTR-2B every month before filing GSTR-3B. Download the GSTR-2B data, match it with your purchase register, and claim only the ITC that is reflected. Claim any missed ITC in the next month once the supplier files.
• Maintain a supplier compliance tracker. Identify suppliers who consistently file late or file incorrect data. Their non-compliance directly impacts your ITC. Have conversations with them or consider switching to compliant suppliers.
• Use the correct place of supply rules. Incorrect place of supply (charging IGST instead of CGST/SGST or vice versa) is a frequent error, especially for services. The rules differ for goods and services, and further differ based on the nature of the service.
• File nil returns on time. Even if there is no business activity in a month, file nil GSTR-1 and GSTR-3B. Non-filing blocks subsequent returns and triggers penalties.
• Keep your registration details updated. Any change in address, bank account, partners, directors, or business activity must be updated on the GST portal within 15 days through the amendment process.
• Utilise the ITC balance in the electronic credit ledger strategically. Understand the order of utilisation (IGST first, then CGST/SGST) and plan your cash flow accordingly.
• Archive all e-invoices and IRNs systematically. If you are above the e-invoicing threshold, ensure your accounting software integrates with the IRP and stores the IRN and QR code with each invoice. Reconstruct this data later is painful and sometimes impossible.
• Set calendar reminders for every compliance deadline. GSTR-1 (11th), GSTR-3B (20th), PMT-06 under QRMP (25th), GSTR-9/9C (31st December). A single missed deadline can cascade into multiple penalties.
• Review credit notes carefully. Credit notes must reference the original invoice and must be reported in the return for the month they are issued. Missing credit notes in GSTR-1 inflate your reported turnover and tax liability.
• Do not make the annual return an afterthought. Start the GSTR-9 and GSTR-9C reconciliation exercise by October. Waiting until December creates a rush that leads to errors, and once filed, these returns cannot be revised.

GST compliance is not a once-a-year exercise. It demands consistent, month-on-month discipline. The businesses that treat GST as a monthly hygiene activity rarely face notices. The ones that treat it as an annual firefighting exercise almost always do.