GST Calculator India: How to Calculate GST Correctly (2026)
Getting GST wrong on an invoice means either underbilling your client or paying tax out of your own pocket. This guide shows exactly how GST is calculated in India, when CGST+SGST applies vs IGST, and how to avoid the most common mistakes freelancers make.
The GST formula (add and remove)
Add GST: Total = Base × (1 + Rate/100)
Remove GST (find base from an inclusive amount): Base = Amount × 100 / (100 + Rate)
The 4 GST slabs
- 5% — essentials, transport, small restaurants
- 12% — processed foods, business-class travel
- 18% — most services including freelance, IT, design, consulting
- 28% — luxury goods, tobacco, high-end vehicles
CGST + SGST vs IGST
The place of supply decides which tax to charge:
- Same state (intra-state) → split equally into CGST + SGST. At 18%, that's 9% CGST + 9% SGST.
- Different states (inter-state) → single IGST at the full rate (18%).
Getting this wrong is the #1 GST error on freelance invoices. Use the GST calculator — pick intra-state or inter-state and the split is automatic.
Worked example
You're a freelance developer in Delhi invoicing a client in Mumbai for ₹50,000 of services at 18% GST:
- Different states → IGST applies
- IGST = 50,000 × 18/100 = ₹9,000
- Total invoice = ₹59,000
Related free tools
Frequently asked questions
How do I calculate GST on an amount?
GST = (Base Amount × Rate) / 100. Example: on ₹10,000 at 18%, GST is ₹1,800, so the total is ₹11,800.
How do I remove GST from a GST-inclusive price?
Base = (Amount × 100) / (100 + Rate). Example: ₹11,800 at 18% → base is ₹10,000, GST is ₹1,800.
When is CGST + SGST charged vs IGST?
If the buyer and seller are in the same state, GST is split equally into CGST (Centre) and SGST (State). If they're in different states, the full amount is IGST.
What GST rate applies to freelance services?
Most professional and freelance services fall under the 18% slab, but confirm the exact SAC code for your service.
Do I need to register for GST as a freelancer?
Yes if annual turnover exceeds ₹20 lakh (₹10 lakh in special states) or if you provide inter-state services.