What GST Is
Goods and Services Tax (GST) is a single indirect tax applied on the supply of most goods and services in India, replacing a range of earlier separate taxes. It’s applied at each stage of the supply chain, with businesses able to claim credit for GST already paid on their inputs — but as a consumer, what matters practically is the final rate applied to the price you pay.
The Basic Calculation
GST amount = (Price × GST rate) / 100. So a product priced at ₹1,000 with a GST rate of 18% would have a GST amount of ₹180, making the final price ₹1,180. Different categories of goods and services attract different GST rates, and these rate categories can change — always check the current applicable rate for a specific item rather than assuming one flat rate applies to everything.
Inclusive vs Exclusive Pricing
A price can be quoted as GST-inclusive (the stated price already contains GST) or GST-exclusive (GST is added on top of the stated price). To find the base price from a GST-inclusive amount, you need to reverse the calculation: Base Price = Inclusive Price / (1 + GST rate/100). Confusing inclusive and exclusive pricing is one of the most common GST calculation mistakes.
CGST, SGST, and IGST
For a transaction within the same state, the total GST is split roughly equally between CGST (Central GST) and SGST (State GST) — for example, an 18% GST rate within a state is typically split as 9% CGST + 9% SGST. For a transaction between two different states, IGST (Integrated GST) applies instead, as a single tax covering the full rate, later apportioned between the central and state governments involved. This split matters for GST-registered businesses filing returns, though the total amount a consumer pays is the same either way.
Why This Matters Even If You’re Not a Business
Understanding GST calculation helps you verify that an invoice or bill is charging the correct tax, spot whether a quoted price is inclusive or exclusive before you commit to a purchase, and understand how much of what you pay for goods and services actually goes to tax.