GST Calculation Explained
Whether you are billing a customer or checking a bill, you need to add GST to a price or take it out. Here are the formulas and examples.
Current rates
Since 22 September 2025 the main GST slabs are 5% and 18%, with 40% for a small set of luxury and sin goods. Older invoices may show 12% or 28%. Check the rate that applies to your item or service.
Add GST to a price
GST amount = price x rate / 100. Final price = price + GST.
Example: ₹10,000 at 18% gives GST of ₹1,800 and a total of ₹11,800.
Remove GST from a GST-inclusive price
Base price = inclusive price x 100 / (100 + rate).
Example: ₹11,800 including 18% GST has a base price of ₹10,000 and GST of ₹1,800.
CGST, SGST and IGST
- Same state: GST is split equally into CGST and SGST. At 18% that is 9% + 9%.
- Different states: the full rate is charged as IGST.
Use the GST Calculator for quick checks, and the GST Invoice Generator to create a printable invoice with the correct split and amount in words.
Note: Results are estimates for learning and planning. They are not financial, tax or investment advice, and actual figures from your bank or lender may differ. See our disclaimer.
Frequently asked questions
How do I find the GST rate for my product?
Check the GST rate schedule or ask your accountant. The rate depends on the product or service category.
Why does the invoice show CGST and SGST?
When the seller and place of supply are in the same state, the tax is shared between the Centre (CGST) and the state (SGST).
Is this tax advice?
No. These tools are for quick calculations. Confirm filing and rate questions with a tax professional.