How to Calculate GST — Formula, Examples and GST Rate List 2026

How to Calculate GST in India

GST is calculated on the base price. India has 5 GST rate slabs: 0%, 5%, 12%, 18% and 28%.

Formula — Adding GST (Exclusive)

GST Amount = Base Price x GST Rate / 100
Example: Rs.1,000 base + 18% GST = Rs.180 GST. Total = Rs.1,180

Formula — Extracting GST (Inclusive)

GST Amount = Total Price x GST Rate / (100 + GST Rate)
Example: Rs.1,180 total with 18% GST = Rs.180 GST. Base = Rs.1,000

CGST vs SGST vs IGST

• Intra-state: 18% split as 9% CGST + 9% SGST
• Inter-state: 18% IGST (goes to Centre)

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