How to Calculate GST: Add or Remove GST with Formulas and Examples

GST is added to almost every bill in India, and shopkeepers, freelancers and buyers all need to work it out quickly. There are only two situations: the price is exclusive of GST, or inclusive of it.

Adding GST to a price (exclusive)

• GST amount = price × rate ÷ 100
• Total = price + GST amount

Example: price ₹1,000 and GST 18% → GST = 1,000 × 18 ÷ 100 = ₹180, total = ₹1,180.

Removing GST from a price (inclusive)

• Original price = total × 100 ÷ (100 + rate)
• GST amount = total − original price

Example: total ₹1,180 including 18% GST → original price = 1,180 × 100 ÷ 118 = ₹1,000, GST = ₹180.

CGST, SGST and IGST

For a sale within the same state, GST is split equally between the Centre and the state: an 18% GST becomes 9% CGST + 9% SGST. For a sale between states, the full rate is charged as IGST.

Which rate applies?

Most goods and services now fall in the 5% or 18% rates, with 0% for exempt items and a higher rate for select luxury and sin goods. Rates are revised by the GST Council, so check the latest notification or your accountant for the exact rate on your product.

Writing the invoice

Once you have the amount, Number to Words converts it into words in the Indian system (lakh, crore) for invoices and cheques.