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How to calculate GST
GST is a percentage added to the value of goods or services. To add GST, take the base amount, multiply it by the rate, and add it back. For example, 18% GST on ₹1,000 is ₹180, so the customer pays ₹1,180. To remove GST from a price that already includes it, divide the total by one plus the rate. A ₹1,180 price that includes 18% GST has a base value of ₹1,000 and ₹180 of tax inside it.
Add GST
GST = Base × Rate ÷ 100
Total = Base + GST
₹1,000 at 18%: GST ₹180, total ₹1,180
Remove GST
Base = Total ÷ (1 + Rate ÷ 100)
GST = Total − Base
₹1,180 including 18%: base ₹1,000, GST ₹180
The calculator above works in both directions and splits the tax as GST requires in India.
CGST, SGST and IGST, in plain words
GST is one tax collected in parts. When you sell to a customer in your own state, the tax is shared between the centre and the state, so it shows as CGST and SGST, each half of the rate. When you sell to a customer in a different state, the whole tax goes to the centre as IGST. The total you collect is the same either way. Only the labels and the split change, based on the place of supply.
Reverse GST calculation: remove GST from an inclusive amount
A reverse GST calculation works backwards from a price that already includes tax to find the base value and the GST inside it. Divide the inclusive amount by 1 plus the rate. For example, ₹1,180 inclusive of 18% GST gives a base of ₹1,000 (₹1,180 ÷ 1.18) and GST of ₹180. Switch the toggle above to GST inclusive and the calculator does this for you. This is useful when your MRP or quoted price already includes GST and you need to show the tax separately on a GST invoice or a cash memo.
GST rates in India
GST 2.0, in force from 22 September 2025, cut the slabs to the ones below. Always confirm the exact rate for your HSN or SAC code, since a few items sit outside these.
| GST rate | Applies to |
|---|---|
| 5% | Essential goods, many food items and some transport services. |
| 18% | The standard rate, where most goods and services fall. |
| 40% | Luxury and sin goods. |
| 0%, 0.25% and 3% | Exempt items, rough diamonds, and gold and silver. |
The old 12% and 28% slabs still apply to supplies made before 22 September 2025, and tobacco products stay at 28% plus cess for now.
From calculation to invoice
When you make a GST bill with Apna Invoice, the CGST, SGST and IGST split happens automatically from your customer's state, the HSN or SAC code sits on each line, and you get a PDF ready to share on WhatsApp. See the GST invoice format guide, explore free billing software for your shop, or read how a GST credit note reverses a bill. Create your first GST invoice free, or see everything Apna Invoice does.
Frequently asked questions
How is GST calculated on an amount?
To add GST, multiply the base amount by the GST rate and add it back. For example, 18% GST on Rs 1,000 is Rs 180, so the total is Rs 1,180. To remove GST from an inclusive amount, divide by 1 plus the rate. Rs 1,180 inclusive of 18% gives a base of Rs 1,000 and GST of Rs 180.
What is the difference between CGST, SGST and IGST?
When the seller and buyer are in the same state, GST splits equally into CGST (central) and SGST (state). When they are in different states, the whole tax is charged as IGST (integrated). This calculator does that split for you.
What are the GST rates in India?
Since 22 September 2025 (GST 2.0) the main slabs are 5% and 18%, with 40% for luxury and sin goods. A few items use 0%, 0.25% or 3%, and tobacco products stay at 28% plus cess for now. Most services fall under 18%. Always confirm the rate for your specific HSN or SAC code.
How do I calculate GST inclusive and exclusive amounts?
Exclusive means GST is added on top of the amount you enter. Inclusive means the amount you enter already contains GST, and the tool works backwards to find the base value and the tax inside it. Switch the toggle to do either.
How do I do a reverse GST calculation?
A reverse GST calculation removes GST from a price that already includes it. Divide the inclusive amount by 1 plus the rate. For example, Rs 1,180 inclusive of 18% GST gives a base of Rs 1,000 (1,180 divided by 1.18) and GST of Rs 180. Switch this calculator to "GST inclusive" to do it automatically.
Is this GST calculator free?
Yes. It is free, works in your browser and needs no sign up. When you are ready to turn a calculation into a proper GST invoice, you can create one free with Apna Invoice.
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