How to use the GST Calculator
- Enter the amount.
- Enter the GST rate that applies to your product or service.
- Choose Add GST if your amount is before tax, or Remove GST if the amount already includes tax.
- Read the total, the price before GST, the GST amount and the CGST and SGST halves.
Formula used
Add GST: GST = Amount × Rate ÷ 100, Total = Amount + GST. Remove GST: Price before GST = Amount × 100 ÷ (100 + Rate), GST = Amount − Price before GST. For intra-state supply, CGST and SGST are each half of the GST.
Worked example
Here is the GST Calculator worked through with the example values shown above, so you can check each step by hand.
| Inputs | |
|---|---|
| Amount | ₹1,000 |
| GST rate | 18 % |
| Calculation | Add GST (amount is GST-exclusive) |
| Result | |
| Total (incl. GST) | ₹1,180 |
| Price before GST | ₹1,000 |
| GST amount | ₹180 |
| CGST (half) | ₹90 |
| SGST (half) | ₹90 |
How to add GST to a price
Multiply the price by the rate and divide by 100 to get the GST, then add it to the price. For an item priced at ₹1,000 with 18% GST, the GST is ₹180 and the total is ₹1,180. For ₹2,000 at 5%, the GST is ₹100 and the total is ₹2,100.
For a sale within one state, the tax is split equally between the central government (CGST) and the state government (SGST). On the ₹1,000 example at 18%, that is ₹90 CGST and ₹90 SGST. For a sale between states, the whole GST is charged as IGST instead.
How to remove GST from an inclusive price
When a price already includes GST, divide it by 1 plus the rate. A bill of ₹1,180 that includes 18% GST has a base price of ₹1,180 ÷ 1.18 = ₹1,000, so the GST is ₹180.
A common mistake is to take 18% off the total. 18% of ₹1,180 is ₹212.40, which would give ₹967.60, and that is wrong. The 18% was charged on the base price of ₹1,000, not on the total, so the reverse calculation has to divide, not subtract a percentage.
Finding the right GST rate
GST rates are decided by the GST Council and are notified for each type of goods and services. The rates and the items under each rate have been revised more than once, so do not rely on an old rate from memory. Check the current rate on the official GST portal, the CBIC website or with your accountant before you invoice.
As an example of how rates change, from 22 September 2025 most goods and services moved to two main rates, 5% and 18%, with a higher 40% rate on a short list of items and a few special rates, replacing the older 12% and 28% slabs. Rates on specific items still depend on their classification, so confirm the rate for your product before you invoice.
Businesses registered under GST can generally claim credit for GST paid on their purchases against the GST they collect, which is why correct base prices and tax amounts on invoices matter.
Frequently asked questions
How do I calculate GST on a price?
GST = Price × Rate ÷ 100, and the total is Price + GST. For ₹1,000 at 18%, GST is ₹180 and the total is ₹1,180.
How do I calculate the original price from a GST-inclusive amount?
Divide the inclusive amount by (1 + Rate ÷ 100). For ₹1,180 at 18%, the original price is ₹1,000 and the GST is ₹180.
What is the difference between CGST, SGST and IGST?
For sales within a state, GST is split into CGST (central) and SGST (state), each half of the rate. For sales between states, the full rate is charged as IGST.
Which GST rate should I use?
The rate depends on the product or service and is set by GST notifications, which have changed over time. Check the official GST portal or ask your accountant for the current rate.
Can I use this for a GST invoice?
You can use it to check the numbers, but a valid tax invoice must follow GST invoicing rules, including your GSTIN and other details. Use your billing software or accountant for the final invoice.
Why is my GST-inclusive reverse calculation different from a simple percentage subtraction?
Because GST is charged on the base price, not on the total. The correct reverse method divides the total by (1 + rate ÷ 100). Subtracting the percentage from the total gives a smaller base price than the true one.
This calculator gives estimates for information only. Actual figures from a bank, employer, tax authority or doctor may differ. It is not financial, tax, legal or medical advice.