CGST, SGST, IGST: GST in Plain English
Look at almost any Indian invoice and you'll see GST broken into pieces — CGST, SGST, sometimes IGST. The acronyms make it look complicated. The underlying idea isn't. Once you know the one rule that decides which applies, the rest falls into place.
The one rule that matters
It all comes down to a single question: did the goods or services cross a state border?
- Same state (seller and buyer in, say, Tamil Nadu): the tax splits in half into CGST (goes to the central government) and SGST (goes to the state). This is an intra-state sale.
- Different states (seller in Tamil Nadu, buyer in Karnataka): the whole tax becomes IGST, collected by the centre and later shared. This is an inter-state sale.
That's genuinely it. CGST + SGST and IGST add up to the same total rate — they're just two ways of slicing the same pie depending on geography.
A quick example
Sell a ₹10,000 product at 18% GST within your state, and you charge ₹1,800 tax — ₹900 CGST and ₹900 SGST. Sell the identical product to another state and you charge ₹1,800 as a single IGST line. The customer pays ₹11,800 either way; only the labelling changes.
Adding GST vs removing it
There are two calculations people mix up. Adding GST is straightforward — multiply the base price by the rate. Removing it (working backwards from a tax-inclusive total to find the base price) trips people up, because you can't just subtract the percentage. The correct move is to divide: base = total ÷ (1 + rate). For an 18% inclusive price of ₹11,800, that's 11,800 ÷ 1.18 = ₹10,000.
Why it's worth getting right
If you run a business, applying the wrong split — IGST where it should be CGST/SGST, or vice versa — creates a real headache at return-filing time. For everyday shoppers it matters less, but it's still satisfying to glance at a bill and know the tax is correct.
Our GST Calculator handles both directions and both splits, so you can add or back-calculate GST without second-guessing the arithmetic.
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