GST Fundamentals in India: What is GST? Explained

The framework has recently undergone its most significant evolution to date. Effective September 22, 2025, the "GST 2.0" streamlined the system even further (Source: Notification No. 9/2025-CT(Rate), CBIC )
Simplified Rate Slabs: The previous four-rate structure (5%, 12%, 18% and 28%) has been consolidated into a leaner three-rate system: 5%, 18%, and 40%.

Additionally, public welfare premiums for health and life insurance are now entirely exempt from GST.

The shift to GST can be seen as a structural response to the flaws of the previous tax regime. To understand why India underwent this change, we need to look at the specific problems GST was designed to solve.

Eliminating the Cascading Effect (Tax on Tax)

In the pre-GST era, taxes were levied at every stage of the supply chain, with no seamless way to offset them. A manufacturer paid excise duty on goods. When a wholesaler bought those goods, they paid VAT on a price that already included the excise duty. Essentially, the wholesaler was paying a tax on a tax. GST allows for a continuous chain of Input Tax Credit (ITC) . A business only pays tax on the "value added" at its specific stage. They can subtract the tax they already paid on purchases (inputs) from the tax they collect on sales (outputs).

Increasing the Tax-to-GDP Ratio

GST has successfully widened the tax base by migrating transactions into a single, trackable digital ecosystem. By the 2024-25 fiscal year, monthly GST collections have consistently exceeded ₹1.5 lakh crore, providing the government with more predictable revenue to fund infrastructure and social programs. (Source: Ministry of Finance GST Revenue Collections, PIB )

Simplifying Compliance via a Unified Digital Interface

Previously, a business operating across multiple states could be dealing with a dozen different state tax departments, each with its own forms, timelines and portals. The GST Network (GSTN) replaced all of that with one portal, one login, standardised returns.

Reducing Corruption and Tax Evasion Through ITC

Through the Input Tax Credit (ITC) system, a buyer can only claim tax credit if their supplier has officially uploaded the invoice to the portal. If a supplier tries to hide a sale to avoid tax, the buyer loses their credit. This creates a powerful incentive for the buyer to ensure the seller reports the transaction accurately. This digital paper trail has made it significantly harder to use fake invoices or under-report sales.

Understanding the Architecture: Types of GST

GST is designed to balance revenue between the Central and State governments. The type of GST applied depends entirely on the place of supply, specifically, whether the transaction stays within a single state or crosses a border.

Glossary: Components of GST

CGST: Central GST is a tax paid to the Central Government on the intra-state supply of products and services.
SGST: State GST is the tax the state government collects on an intra-state sale.
IGST: Integrated GST is paid to the Central Government for an inter-state sale (e.g., Maharashtra to Tamil Nadu).
UTGST: Union Territory GST is an indirect tax collected by the Union Territory on the supply of goods or services in Union Territories.

Intra-State Transactions

When a business and a buyer are located in the same state (e.g., a sale from Mumbai to Pune), the tax is split equally between the Centre and State. Two specific components apply:

CGST (Central GST): This portion is collected by the Central Government and goes into the Union's consolidated fund.
SGST (State GST): This portion is collected by the State Government where the transaction occurs.

Both are levied at half the total GST rate. For an item in the 18% bracket, the invoice will show 9% CGST and 9% SGST.

Note on Union Territories: For territories without their own legislature, such as Ladakh, Chandigarh or the Andaman & Nicobar Islands, UTGST replaces SGST. The 50/50 split with CGST remains the same.

Inter-State Transactions (Between States, Exports, Imports)

When goods or services move from one state to another (e.g., Delhi to Haryana) or when goods are imported into India, a single integrated tax is applied:

IGST (Integrated GST): This is the total tax rate applicable to the transaction (e.g., the full 18%).

While the Central Government collects the entire IGST amount, it does not keep it all. Under the GST framework, the Centre apportions the destination state's share and transfers it to the destination state. This mechanism is the engine of the destination-based tax philosophy, ensuring that tax revenue follows the consumer rather than the manufacturer.

Place of Supply: Why It Determines Which Tax You Pay

Every GST transaction requires determining the place of supply in GST , either the buyer's location or where the service is consumed. This single determination decides whether CGST + SGST or IGST applies.

For goods: The place of supply is generally where the goods are delivered. If you ship goods from Mumbai to a buyer in Mumbai, the place of supply is Maharashtra, so CGST + SGST apply. If you ship to Delhi, the place of supply is Delhi, so IGST applies.

For services: The place of supply is generally where the recipient of the service is located. A marketing agency in Bengaluru providing services to a company in Hyderabad means the place of supply is Hyderabad (Telangana), so IGST applies.

Why it matters for your business: Getting the place of supply wrong means charging the wrong tax component. If you charge CGST + SGST on what should be an inter-state transaction, the buyer's ITC claim may be invalid, leading to disputes, credit notes , and amended invoices.

Special rules apply for specific services including construction, transportation, telecommunications, and online services. These are governed by Sections 10 to 13 of the IGST Act, 2017.

Time and Value of Supply

Two foundational concepts determine exactly when your GST liability arises and on what amount it is calculated.

Time of Supply

The time of supply is the date on which your GST liability arises, i.e. which month's GSTR-3B return to include the transaction in.

For goods: The earlier of the date of invoice or the date of receipt of advance payment.
For services: The earlier of the date of invoice (if issued within 30 days of service completion) or the date of receipt of payment.

Practical implication: If you receive an advance payment before issuing an invoice, your GST liability arises on the date of advance receipt. You must account for GST in that month's return, not when the invoice is eventually raised.

Value of Supply

GST is calculated on the transaction value, the price actually paid or payable for the goods or services. The taxable value includes:

• Packing and forwarding charges
• Freight and insurance (if borne by the supplier)
• Commissions or brokerage charged to the buyer

Discounts: Discounts given before or at the time of supply and recorded on the invoice may be excluded from the taxable value. Post-supply discounts (credit notes) can be excluded only if a prior agreement exists and the buyer reverses the corresponding ITC.

Current GST Rate Slabs (Post GST 2.0)

Under the "GST 2.0" reform, the previous four-tier structure was dismantled to reduce complexity and litigation. The goal is simply to move more items into a "Merit" or "Standard" category, while keeping luxury items in a separate high-tax bracket.

The New Three-Tier Structure

The old 12% and 28% slabs have been largely abolished. Most goods from the 12% category have dropped to 5%, and nearly 90% of items formerly at 28% (like ACs and small cars) have moved down to 18%.

Note on Precious Metals: Gold and silver jewellery are taxed at 3%, while rough industrial diamonds are taxed at 0.25%.

What Remains Outside the GST Net?

Certain high-revenue items are subject to separate state-level taxes (such as VAT and Central Excise) and are not covered by GST. This means businesses cannot claim Input Tax Credit (ITC) on these purchases:

• Petroleum Products: Petrol, diesel, crude oil, natural gas and aviation turbine fuel (ATF)
• Alcohol: Specifically for human consumption
• Electricity: Subject to state electricity duties

Did You Know? Perhaps the most significant change in GST 2.0 is the total exemption of individual health and life insurance premiums.

Before: You paid 18% GST on your insurance, adding thousands to your annual cost.
Now: The rate is 0%. This move is designed to achieve "Insurance for All" by 2047, making vital protection roughly 18% cheaper for every household.

GST Registration Explained

GST registration is not a legal requirement for every Indian but it can act as a gateway requires a GST certificate to claiming Input Tax Credit (ITC). For small businesses, especially, the decision to register (or not) can impact margins and growth. However, the government provides breathing room for small businesses through specific turnover thresholds.

Threshold Limits: When is Registration Mandatory?

As a business, your requirement to register is based on your Annual Aggregate Turnover (AATO). This is calculated on a PAN-India basis, meaning if you have three shops in different states, their combined turnover determines your status.

Special Category States: All North-Eastern states (Assam, Manipur, Meghalaya, Mizoram, Nagaland, Tripura, Arunachal Pradesh, Sikkim) plus Uttarakhand and Himachal Pradesh.

The Composition Scheme: A Simpler Alternative for Small Businesses

If your turnover is below ₹1.5 crore (₹75 lakh for special category states), you can opt for the Composition Scheme, a simplified GST compliance option designed to reduce the burden on small businesses.

How it works: Instead of charging GST at the standard rate and claiming ITC, you pay a flat GST rate on your total turnover

You collect no GST from customers and cannot claim ITC.

Who should use it: Small retailers, local manufacturers, and food service businesses with primarily local, B2C customers who do not require a GST invoice from you.

Key restrictions:

• Cannot make inter-state supplies
• Cannot supply to e-commerce platforms
• Must display "Composition Taxable Person" on all signage and invoices
• File CMP-08 quarterly instead of monthly GSTR-1 and GSTR-3B

Trade-off: The composition scheme reduces your compliance burden and tax outgo significantly. But if your buyers are registered businesses who need to claim ITC from your invoices, they cannot do so, making you a less attractive supplier to B2B customers

What Does This Mean for Small Businesses?

If you're just starting out or operating below these limits, you're not required to register immediately. This helps you keep compliance simple in the early stages. However, staying unregistered also means:

• You cannot claim ITC
• Larger clients may prefer GST-registered vendors
• Expansion, especially across states, becomes restricted

So, even if you're below the threshold, voluntary registration is sometimes the best choice.

When Thresholds Don't Apply or May Not Apply

In certain cases, turnover limits do not fully protect a business from GST registration. While thresholds of ₹20 lakh to ₹40 lakh apply in many situations, registration is still compulsory for certain categories of persons, including several inter-state suppliers and some e-commerce-linked businesses. Because this area is driven by specific exemptions and notifications, businesses should check the latest rules before relying on any threshold-based exemption.

Inter-State Supplies: In many cases, persons making inter-state taxable supplies are required to register. However, this should not be treated as a blanket rule for every category without checking the current exemptions.

E-commerce: Some persons supplying through e-commerce operators, and e-commerce operators themselves in specified cases, may be required to register. The exact rule depends on the nature of supply, the platform model, and any applicable exemptions.

Casual Taxable Persons: Businesses that occasionally supply goods/services in a state where they have no fixed place of business (e.g. setting up a stall at a 10-day trade fair).

Non-Resident Taxable Persons: Foreign entities supplying goods or services to Indian consumers.

Online Gaming Providers: Entities providing online money gaming from outside India to Indian players.

For small businesses, this is where many get caught off guard. For example, the moment you start selling outside your home state or list on an e-commerce platform, you need to verify whether the threshold exemption still applies to your category.

The Mechanics: GST Calculation and Input Tax Credit (ITC)

The Basic Formula

Whether you are creating an invoice or reconciling your purchases, these two formulas are your primary tools:

GST Amount = (Original Price × GST Rate) ÷ 100
Price Inclusive of GST = Original Price + GST Amount

To extract the original price from an inclusive price:

Original Price = Inclusive Price ÷ (1 + GST Rate/100)

Simplify Your Calculations with Busy: Stop manually calculating tax for every line item. Busy's GST calculator automatically calculates CGST, SGST and IGST based on GST type, rate and supply type, ensuring 100% accuracy in your invoices.

Input Tax Credit (ITC): How It Actually Works

ITC is the mechanism through which the cascading effect is eliminated. Every GST-registered business keeps two accounts in mind:

• Output Tax: GST collected on sales
• Input Tax: GST paid on purchases, imports, and eligible services

Net tax payable = Output Tax - ITC Available. You only deposit the difference with the government.

ITC Offsetting Rules: Which Credits Offset Which Liabilities

ITC must be applied in a specific order. You cannot freely mix credits across tax heads:

Example: If you have ₹5,000 CGST credit and ₹8,000 CGST liability plus ₹6,000 IGST liability, you must first use all ₹5,000 CGST credit against your CGST liability. You cannot apply CGST credit directly to your SGST liability.

Blocked ITC: What You Cannot Claim

Not all GST paid on inputs qualifies for ITC. Section 17(5) of the CGST Act, 2017 blocks ITC on:

• Motor vehicles for personal use
• Food, beverages, and outdoor catering
• Beauty treatment, health services, and cosmetic surgery
• Membership of clubs, health and fitness centres
• Travel benefits to employees (leave travel, home travel concession)
• Construction of immovable property (except for a works contractor)
• Goods or services used for personal consumption

Why this matters: If your business buys a car for employee commutes, the GST paid on that car is blocked, it cannot be used to offset your output tax liability.

Reverse Charge Mechanism (RCM): When You Pay GST as the Buyer

Under normal GST, the seller collects tax from you and remits it to the government. Under the Reverse Charge Mechanism (RCM), you, the buyer, are directly responsible for paying the GST, even if the seller charged you nothing.

When RCM Applies

RCM commonly applies in three broad situations, but only where the law or a notification specifically provides for it:

1. Notified goods and services (Section 9(3), CGST Act, 2017): The government has issued specific notifications listing supplies that always attract RCM regardless of supplier status. Common examples:

2. Purchases from unregistered suppliers (Section 9(4)): Reverse charge under this section applies only in notified cases. Businesses should always check the latest notification before treating any unregistered purchase category as automatically covered.

3. E-commerce platforms (Section 9(5)): Platforms like Ola, Uber, Swiggy, and Zomato pay GST for their service providers under this provision.

Key RCM Rules

• RCM tax must be paid in cash, you cannot use your existing ITC balance to settle it.
• Once paid in cash, RCM tax is eligible for ITC if the purchase is used for business purposes.
• In reverse charge cases involving an unregistered supplier, the recipient may need to issue a self-invoice and maintain the required documentation under the GST rules. The exact timing and documentation requirements should be checked against the latest applicable provisions and notifications.
• Issue a payment voucher to the supplier at the time of payment.
• Report the liability in GSTR-3B Table 3.1(d) and claim ITC in Table 4A(3) in the same filing period.

Quick Example

Your business hires a transport company (GTA) and pays ₹50,000 freight. The GTA has opted for the 5% rate without ITC. You pay ₹2,500 GST under RCM in cash, then claim ₹2,500 as ITC in the same month's GSTR-3B. Net cash cost: zero, but you must complete both the cash payment and reporting steps correctly.

Common Mistake: Some businesses claim ITC on reverse charge in Table 4A(3) but fail to report the corresponding liability correctly in Table 3.1(d). This can create a mismatch in returns and may lead to scrutiny, tax demand, interest, or notice. Always report both the liability and the related ITC correctly.

Automate RCM with Busy: Busy Accounting Software auto-detects RCM when you tag a vendor as unregistered or a purchase as an RCM category, generates self-invoices and payment vouchers with all mandatory fields pre-filled, and pre-populates both GSTR-3B tables from your purchase register.

GST Compliance: Returns and E-Way Bills

In the GST ecosystem, "compliance" revolves around reporting your transactions through GST returns and documenting the movement of goods via E-Way Bills. A dedicated GST accounting software automates your return filing, ITC tracking, and multi-GSTIN management from one dashboard.

Major GST Returns

The frequency and type of return you file depend on your business size and the nature of your operations.

QRMP Scheme: Small businesses with an AATO up to ₹5 crore can opt for the Quarterly Return, Monthly Payment QRMP scheme . This allows you to file your detailed returns once every three months while paying your estimated tax monthly via a simple challan (PMT-06). Before filing, reconcile your GSTR-2B with your purchase register using GSTR reconciliation software to catch ITC mismatches early.

E-Invoicing: Mandatory for Businesses Above ₹5 Crore

If your business has an Annual Aggregate Turnover (AATO) above ₹5 crore, you are required to generate e-invoices for all B2B transactions. E-invoicing authenticates your GST invoice through the Invoice Registration Portal (IRP) and generates a unique Invoice Reference Number (IRN) with a QR code.

Key facts:

• Applicable to B2B invoices, debit notes , and credit notes
• Businesses with AATO above ₹10 crore must submit invoices to the IRP within 30 days of the invoice date (effective April 1, 2025)
• An invoice without a valid IRN is treated as invalid under Rule 48(4), the buyer cannot claim ITC on it
• E-invoices auto-populate your GSTR-1 and the e-way bill portal, eliminating manual data entry

For full e-invoicing rules, applicability thresholds, and the generation process, see: E-Invoicing Under GST.

BUSY's e-invoicing software auto-generates IRNs, prints QR codes, and syncs with GSTR-1 in one step

E-Way Bills

An e-way bill is a mandatory digital document generated on the e-way bill portal for any movement of goods valued above ₹50,000 (Source: Rule 138, CGST Rules, 2017).

The party initiating the movement (Supplier, Recipient, or Transporter) must generate the bill before the goods leave the premises.

The bill is valid for 1 day for every 200 km of travel (e.g. a 400 km journey requires a 2-day validity window). This is the travel validity period. From 1 January 2025, the system does not allow E-Way Bill generation for base documents older than 180 days from the date of generation. This 180-day rule relates to document age for E-Way Bill generation, not to travel validity.

If the transport meets with an accident or faces a natural calamity, the validity can be extended on the portal within the allowed system window.

While the national limit is ₹50,000, individual states sometimes set higher limits for movement within their borders (e.g. Maharashtra or Gujarat may have different thresholds for local transport).

With Busy accounting software, you can generate and upload your GSTR-1 and 3B directly to the portal with a single click.

The transition to GST has fundamentally rewritten the rules of the Indian marketplace. India has moved from a fragmented collection of state-level economies to a unified national market. The removal of CST complications, the seamless flow of Input Tax Credit and the recent "GST 2.0" rate rationalisation all point toward a more mature, predictable fiscal environment.