How to calculate GST
Adding GST to a price
GST amount = price × GST rate ÷ 100
Total = price + GST amount
Example: ₹10,000 at 18% GST. GST = 10,000 × 18 ÷ 100 = ₹1,800. Total = ₹11,800.
Removing GST from a GST-inclusive amount
Price before GST = total × 100 ÷ (100 + GST rate)
GST amount = total − price before GST
Example: ₹11,800 including 18% GST. Price before GST = 11,800 × 100 ÷ 118 = ₹10,000. GST = ₹1,800.
CGST, SGST and IGST
- Sale within your state (intra-state): GST is split equally into CGST (central) and SGST (state). At 18%, that is 9% CGST and 9% SGST. In union territories without a legislature, UTGST takes the place of SGST.
- Sale to another state (inter-state): the whole tax is charged as IGST. At 18%, that is 18% IGST.
The total tax is the same either way. Only the split, and which government receives it, changes.
Which GST rate applies?
The rate depends on the HSN code of the goods or the SAC code of the service. Following the GST rate changes that took effect on 22 September 2025, most goods and services fall under the 5% or 18% slab, with 40% for a small list of luxury and sin goods, and special rates such as 0.25% and 3% for precious stones and metals. The calculator also keeps the older 12% and 28% rates for checking past invoices.
Rates change through GST Council notifications, so always confirm the current rate for your HSN or SAC code with your CA or on the official GST portal.