How to use the GST calculator
Choose Add GST if your price does not include tax yet, or Remove GST if you have a final price and need to know how much of it is tax. Enter the amount, tap a rate or type your own, and pick whether the buyer is in the same state as you. The result updates as you type, with the tax split the way it should appear on your invoice.
The formulas for adding and removing GST
To add GST, multiply the net price by the rate: GST = amount × rate ÷ 100, and the total is the amount plus that GST. Removing GST is not the reverse of adding it. The tax inside an inclusive price is amount × rate ÷ (100 + rate), because the rate applies to the net price, not the total. Taking 18% straight off an inclusive price is the most common GST mistake and overstates the tax every time.
A worked example
Add GST: a ₹10,000 service at 18% carries ₹1,800 of GST, so the invoice total is ₹11,800. Sold within your state, that splits into ₹900 CGST and ₹900 SGST. Remove GST: a product priced at ₹1,050 including 5% GST has a net price of ₹1,000 and ₹50 of tax. Taking 5% of ₹1,050 instead gives ₹52.50, which is wrong.
CGST and SGST, or IGST?
It depends on where the supply goes. When the seller and buyer are in the same state, the GST is split equally between the centre (CGST) and the state (SGST or UTGST), so 18% becomes 9% plus 9%. When the goods or services cross a state border, the whole amount is charged as IGST. The total tax is the same either way. Only the way it is labelled and paid changes.
Current GST rates in India
Since 22 September 2025, GST has two main slabs: 5% for most everyday goods and 18% for most other goods and services. A 40% rate applies to selected luxury and sin goods, and a few items keep special rates, such as 3% on gold. The old 12% and 28% slabs were removed, with most items moving down to 5% or 18%. Rates are set item by item, so check the rate for your HSN or SAC code before you invoice.