You can know GST is 18% and still get your invoice wrong if you don't know which 18% — IGST or 9% + 9%.

The difference is not cosmetic: it decides which government gets the revenue and how ITC flows between states.

This guide shows how one place-of-supply decision flips your invoice between IGST and CGST+SGST for both goods and services.

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The core rule: same state = CGST+SGST, different state = IGST

When supplier location and place of supply are in the same state/UT, you charge CGST and SGST in equal halves.
When they are in different states/UTs, you charge IGST on the entire taxable value.
For goods, place of supply usually follows where the goods are delivered; for services, it depends more on the service nature and contract.
Get this wrong and you are paying the right total tax to the wrong bucket — fixing it later is painful.

Simple Indian examples: interstate vs intrastate in one glance

Intrastate: You (GSTIN registered in Karnataka) sell laptops to a shop in Mysuru, shipping from your Bengaluru warehouse to Mysuru. Place of supply = Karnataka → charge CGST+SGST.
Interstate: You (Karnataka) sell laptops to a buyer in Maharashtra, shipping to Pune. Place of supply = Maharashtra → charge IGST.
Service, client in another state: You (Karnataka) offer branding services to a client registered in Delhi. Place of supply typically = client's registered location → IGST.
Service at your office: A client from another state physically visits your design studio in Bengaluru and pays on the spot; in many cases, place of supply can be Karnataka → CGST+SGST.

How your invoice should show CGST, SGST, or IGST

For CGST+SGST: show the taxable value, GST rate (say 18%), and split tax lines like 'CGST @9%' and 'SGST @9%'.
For IGST: single line 'IGST @18%' on the taxable value.
Never show all three on the same supply; it is always either CGST+SGST or IGST, not a combination.
Your software should never ask users to 'pick one' manually if state and place-of-supply are already known.

Product behaviour that prevents expensive mistakes

Lock each customer to a state and GSTIN once, then derive interstate vs intrastate automatically each time they are picked.
Show a tiny explanation on hover: 'Interstate supply — IGST applies because supplier: KA, place of supply: DL'.
If the user changes shipping state, automatically recalc tax and highlight the change so they feel safe.
On this guide, put a CTA 'Try an interstate vs intrastate example' that opens the canvas with pre-filled demo data.

The core rule: same state = CGST+SGST, different state = IGST

When supplier location and place of supply are in the same state/UT, you charge CGST and SGST in equal halves.

When they are in different states/UTs, you charge IGST on the entire taxable value.

For goods, place of supply usually follows where the goods are delivered; for services, it depends more on the service nature and contract.

Get this wrong and you are paying the right total tax to the wrong bucket — fixing it later is painful.

Simple Indian examples: interstate vs intrastate in one glance

Intrastate: You (GSTIN registered in Karnataka) sell laptops to a shop in Mysuru, shipping from your Bengaluru warehouse to Mysuru. Place of supply = Karnataka → charge CGST+SGST.

Interstate: You (Karnataka) sell laptops to a buyer in Maharashtra, shipping to Pune. Place of supply = Maharashtra → charge IGST.

Service, client in another state: You (Karnataka) offer branding services to a client registered in Delhi. Place of supply typically = client's registered location → IGST.

Service at your office: A client from another state physically visits your design studio in Bengaluru and pays on the spot; in many cases, place of supply can be Karnataka → CGST+SGST.

How your invoice should show CGST, SGST, or IGST

For CGST+SGST: show the taxable value, GST rate (say 18%), and split tax lines like 'CGST @9%' and 'SGST @9%'.

For IGST: single line 'IGST @18%' on the taxable value.

Never show all three on the same supply; it is always either CGST+SGST or IGST, not a combination.

Your software should never ask users to 'pick one' manually if state and place-of-supply are already known.

Product behaviour that prevents expensive mistakes

Lock each customer to a state and GSTIN once, then derive interstate vs intrastate automatically each time they are picked.

Show a tiny explanation on hover: 'Interstate supply — IGST applies because supplier: KA, place of supply: DL'.

If the user changes shipping state, automatically recalc tax and highlight the change so they feel safe.

On this guide, put a CTA 'Try an interstate vs intrastate example' that opens the canvas with pre-filled demo data.

CGST vs SGST vs IGST — and the one decision that flips your invoice between them

Stop fighting with invoice templates.

The core rule: same state = CGST+SGST, different state = IGST

Simple Indian examples: interstate vs intrastate in one glance

How your invoice should show CGST, SGST, or IGST

Product behaviour that prevents expensive mistakes

Keep reading

GST tax invoice rules in India: every mandatory field explained

HSN and SAC codes explained — a practical guide for Indian businesses

CGST vs SGST vs IGST — and the one decision that flips your invoice between them

Stop fighting with invoice templates.

The core rule: same state = CGST+SGST, different state = IGST

Simple Indian examples: interstate vs intrastate in one glance

How your invoice should show CGST, SGST, or IGST

Product behaviour that prevents expensive mistakes

Keep reading

GST tax invoice rules in India: every mandatory field explained

HSN and SAC codes explained — a practical guide for Indian businesses