How to Calculate GST in India

By Unitafy · March 2026 · 5 min read

GST (Goods and Services Tax) replaced multiple indirect taxes in India in 2017. Understanding how to calculate GST is essential for businesses, shopkeepers, and consumers alike.

GST Rate Slabs in India

GST RateCategoryExamples
0%Exempt / EssentialFresh vegetables, milk, eggs, bread
5%Essential goodsPackaged foods, medicines, coal
12%Standard goodsButter, cheese, mobile phones, computers
18%Standard servicesRestaurants, electronics, most services
28%Luxury/sin goodsCars, tobacco, aerated drinks, luxury hotels

Formula: Adding GST to a Price

GST Amount = Original Price × (GST Rate ÷ 100)

Total Price = Original Price + GST Amount

Example: Product costs ₹1,000 with 18% GST:

GST = 1,000 × 18/100 = ₹180 | Total = ₹1,180

Formula: Finding Original Price from GST-Inclusive Price

Original Price = Inclusive Price ÷ (1 + GST Rate/100)

Example: You paid ₹1,180 (GST included at 18%). What's the base price?

Base = 1,180 ÷ 1.18 = ₹1,000 | GST paid = ₹180

CGST, SGST, and IGST

  • CGST (Central GST) — Goes to central government. Half of the total GST rate.
  • SGST (State GST) — Goes to state government. Other half of GST rate.
  • IGST (Integrated GST) — For inter-state transactions. Equal to CGST + SGST combined.

Example: 18% GST on an intra-state sale = 9% CGST + 9% SGST. On inter-state = 18% IGST.

🧾 Quick check: On any GST invoice, verify that Total = Base Amount × (1 + GST%). If the numbers don't match, something may be wrong with the invoice.