GST Explained: Rates, Slabs, and How to Calculate GST in India

Goods and Services Tax (GST) is one of the most significant tax reforms in India's history. Since its introduction on 1 July 2017, GST has replaced a complex web of over 17 central and state taxes. Yet many people still find it confusing. This guide breaks it down simply.

What is GST?

GST (Goods and Services Tax) is a single, unified indirect tax levied on the supply of goods and services across India. It replaced taxes like Central Excise Duty, Service Tax, VAT, and several others with one streamlined system. The key principle: tax is collected at every stage of the supply chain, but credit is given for tax already paid at earlier stages — this is called the Input Tax Credit (ITC) system.

GST Rate Slabs

India uses a multi-tier GST structure with four main slabs:

CGST, SGST, and IGST: What's the Difference?

GST is structured as a dual tax — split between the Centre and States:

• CGST (Central GST): Collected by the Central Government on intra-state sales
• SGST (State GST): Collected by the State Government on intra-state sales
• IGST (Integrated GST): Collected by the Centre on inter-state sales and imports

So when you buy something with 18% GST within your state, you pay 9% CGST + 9% SGST. If the seller is in another state, you pay 18% IGST.

How to Calculate GST

There are two scenarios:

Adding GST (Exclusive)

Removing GST (Inclusive)

GST Registration: When is it Required?

Any business with an annual turnover exceeding ₹40 lakh (₹20 lakh for services, ₹10 lakh for special category states) must register for GST. Online sellers on platforms like Amazon and Flipkart must register regardless of turnover.

GST Returns and Compliance

Registered businesses must file GST returns regularly:

• GSTR-1: Monthly/quarterly return for outward supplies
• GSTR-3B: Monthly summary return and tax payment
• GSTR-9: Annual return

Non-filing or late filing attracts penalties and interest. Use a CA or GST-certified professional for compliance.

GST on E-commerce: TCS and Online Sellers

If you sell through platforms like Amazon, Flipkart, or Myntra, e-commerce operators are required to deduct Tax Collected at Source (TCS) at 1% (0.5% CGST + 0.5% SGST, or 1% IGST for inter-state sales) on the net value of taxable supplies made through their platform. This TCS amount is deposited with the government and reflects as credit in the seller's electronic cash ledger, which can be used to offset their own GST liability. This is separate from the seller's own GST registration and return filing obligation, which remains mandatory regardless of turnover for anyone selling via e-commerce.

Reverse Charge Mechanism (RCM)

Normally, the supplier of goods or services collects GST from the buyer and deposits it with the government. Under the Reverse Charge Mechanism, this responsibility flips — the recipient of goods or services pays the GST directly to the government instead of the supplier. RCM commonly applies to:

• Services from an unregistered supplier to a registered business
• Legal services from an advocate to a business entity
• Goods Transport Agency (GTA) services in most cases
• Import of services from outside India

Businesses paying GST under RCM can usually claim it back as Input Tax Credit in the same return period, making it largely cash-flow neutral, but it does require careful tracking since the liability isn't reflected on a normal supplier invoice.

Composition Scheme for Small Businesses

Small businesses with an annual turnover up to ₹1.5 crore (₹75 lakh for special category states) can opt for the GST Composition Scheme instead of regular GST registration. Under this scheme:

• Tax is paid at a much lower flat rate (typically 1% for traders, 5% for restaurants, 6% for certain service providers under a related scheme) on total turnover rather than at standard slab rates.
• Only a simplified quarterly return needs to be filed, instead of the more detailed monthly GSTR-1/GSTR-3B filings.
• The trade-off: composition dealers cannot claim Input Tax Credit on their purchases and cannot charge GST separately on their invoices, which can make their pricing less attractive to GST-registered business buyers who want to claim ITC.

Common GST Mistakes to Avoid

• Claiming ITC on ineligible items: Items like employee food/beverages, personal-use vehicles (with some exceptions), and club memberships are typically blocked from Input Tax Credit even if GST was charged on them.
• Mismatched invoices: If your GSTR-1 doesn't match your buyer's GSTR-2B, their ITC claim can get blocked or delayed — always reconcile invoice-level data before filing.
• Missing the annual return (GSTR-9) deadline: This attracts late fees even if all monthly/quarterly returns were filed on time.
• Wrongly charging CGST+SGST instead of IGST (or vice versa): This is a common error for businesses that ship across state lines — always confirm the place of supply rules before invoicing.

Frequently Asked Questions

Q: Is GST applicable on all goods and services in India?
A: No — a few items remain outside GST entirely, most notably petrol, diesel, natural gas, and alcohol for human consumption, which continue to attract state-level excise duty and VAT instead.

Q: What is Input Tax Credit (ITC) in simple terms?
A: If you paid GST on business purchases (inputs), you can subtract that amount from the GST you owe on your sales (output), so you only pay tax on the value you actually add — this prevents the "tax on tax" cascading effect that existed before GST.

Q: Can I claim a GST refund?
A: Yes, in specific situations — such as exports (which are zero-rated), an inverted duty structure (where input tax exceeds output tax), or excess balance in the electronic cash ledger — refunds can be claimed through the GST portal within the prescribed time limit.

Q: What is an e-way bill and when is it required?
A: An e-way bill is an electronic document generated on the GST portal that's mandatory for transporting goods worth more than ₹50,000 between states (and in most states, within the state too). It records details like the invoice, consignor, consignee, and transporter, and helps tax authorities track the movement of goods to prevent evasion.

Q: Do I need a separate GST registration for each state I operate in?
A: Yes — GST registration in India is state-specific. If your business has a physical presence (office, warehouse, or branch) in more than one state, you generally need a separate GSTIN for each state, even though the underlying PAN remains the same across all registrations.

Calculate GST Instantly

Need to add or remove GST from an amount? Use our free GST Calculator — supports all slabs (5%, 12%, 18%, 28%) and both exclusive and inclusive calculations.