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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.
The formulas are simple, but doing them by hand for every line of an invoice is where mistakes creep in. The calculator above handles both directions, and splits the tax the way GST actually works 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.
GST rates in India
The common slabs are below. Always confirm the exact rate for your HSN or SAC code, since a few items sit outside these.
- 5%, often basic and essential goods and some transport services.
- 12%, a middle band covering many processed goods and services.
- 18%, the most common rate, where most services land.
- 28%, higher band for items like luxury and certain durables.
From calculation to a real invoice
A calculator gives you a number. An invoice gives you a record. 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 clean PDF you can share on WhatsApp in seconds. 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?
The common GST slabs are 5%, 12%, 18% and 28%. A few items use 0%, 0.25% or 3%. 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.
Is this GST calculator free?
Yes. It is completely 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.