Adding versus removing GST
These are different calculations and mixing them up is the most common GST error.
Adding GST applies to an exclusive amount. At 18%, a base of ₹1,000 becomes ₹1,180. Straightforward multiplication.
Removing GST extracts the tax from a price that already includes it, and it is not simply subtracting 18%. You divide by 1.18, not multiply by 0.82. On a ₹1,180 inclusive price the base is ₹1,000 and the GST is ₹180 — whereas subtracting 18% would wrongly give ₹967.60.
This matters whenever you are working backwards from a retail price to find the taxable value, which is routine in reconciliation and in checking a supplier's invoice.
CGST, SGST and IGST
GST is a destination-based tax split according to where the supply moves.
For a supply within a state, the tax divides equally between Central GST and State GST. An 18% rate becomes 9% CGST plus 9% SGST. The customer pays 18% either way — the split determines who receives it, not what is charged.
For a supply between states, the whole amount is Integrated GST, collected centrally and apportioned to the destination state.
Getting the split wrong on an invoice is a common compliance error, because the total is identical and nothing looks obviously wrong on the face of it.
The rate slabs
India's GST operates in bands, broadly following how essential a category is considered.
- 0% — most unbranded staple foods, and certain essential services
- 5% — household necessities and common consumption items
- 12% — processed foods and a range of standard goods
- 18% — the most common band, covering most services and manufactured goods
- 28% — luxury and demerit goods, sometimes with an additional cess
Classification is category-specific and changes with GST Council decisions. If a rate matters for compliance rather than a rough estimate, verify the current rate for your HSN or SAC code rather than assuming.
Reading a total that already includes tax
A quick way to sanity-check any inclusive figure: at 18%, the tax is a little over 15% of the total — not 18% of it. The percentages differ because one is measured against the base and the other against the total.
Getting this backwards is the source of most manual GST mistakes, and it is why the remove GST mode exists above.
This calculator handles the arithmetic. It is not tax advice, and rate classification for your specific goods or services should be confirmed against current GST Council notifications or with a qualified professional.
Frequently asked questions
How do I remove GST from an inclusive price?
Divide by 1 plus the rate, not subtract the rate. At 18%, divide the inclusive amount by 1.18. On Rs 1,180 the base is Rs 1,000 and GST is Rs 180 - whereas subtracting 18% would wrongly give Rs 967.60.
What is the difference between CGST, SGST and IGST?
For supplies within a state the tax splits equally between Central GST and State GST, so 18% becomes 9% plus 9%. For supplies between states the full amount is Integrated GST. The customer pays the same total either way; the split determines who receives it.
What are the GST rate slabs in India?
The main bands are 0%, 5%, 12%, 18% and 28%, with 18% the most common. Classification is category-specific and changes with GST Council decisions, so verify the rate for your HSN or SAC code for compliance purposes.
Is GST 18% of the total or of the base amount?
Of the base amount. At an 18% rate the tax works out to a little over 15% of the tax-inclusive total, because the two percentages are measured against different figures. Confusing the two is the most common manual GST error.