How do I remove GST from an inclusive price?

Divide by one plus the rate, do not subtract the percentage. At 18%, a ₹11,800 total contains ₹10,000 of value and ₹1,800 of GST, found by dividing ₹11,800 by 1.18. Taking 18% off ₹11,800 instead gives ₹9,676, which is wrong by ₹324 — and the error grows with the rate.

What is the difference between CGST, SGST and IGST?

For a supply within one state, GST splits equally into CGST (central) and SGST (state) — an 18% rate becomes 9% plus 9%. For a supply between states, a single IGST is charged at the full 18%. The total tax is identical either way; only the split on the invoice changes, and getting it wrong is a common filing error.

Which GST rate applies to my goods or service?

Rates are set by HSN code for goods and SAC code for services, across five slabs: 0, 5, 12, 18 and 28 percent. Most services sit at 18%. Essentials are commonly 0 or 5, and luxury or demerit goods attract 28 plus a cess. Look up your specific code on the CBIC portal rather than assuming.

Is GST charged on the discounted price or the original?

On the discounted price, provided the discount is shown on the invoice and was agreed before or at the time of supply. A discount given afterwards can only reduce the taxable value if it was pre-agreed and can be linked to the specific invoices.

GST Calculator: Add or Remove GST

How to use this calculator

Enter the amount.
Pick the GST rate — 0, 5, 12, 18 or 28 percent.
Choose the direction: adding GST to a value, or removing it from a total that already includes it.
Choose whether the supply is intra-state or inter-state, which decides how the tax splits on the invoice.

How the calculation works

Adding GST is straightforward:

GST   = value × rate
total = value + GST

Removing it is where most people go wrong. The correct method is a division:

value = total / (1 + rate)
GST   = total − value

Not total × (1 − rate), which is what intuition suggests and which is always wrong. The GST was calculated as a percentage of the smaller pre-tax value; subtracting that same percentage from the larger total applies it to the wrong base.

A worked example, both directions

Adding 18% GST to a ₹10,000 supply:

GST   = 10,000 × 0.18 = 1,800
total = 10,000 + 1,800 = 11,800

Removing 18% GST from that ₹11,800 total:

value = 11,800 / 1.18 = 10,000
GST   = 11,800 − 10,000 = 1,800

The division recovers ₹10,000 exactly. Now the wrong method:

11,800 × (1 − 0.18) = 9,676   ← wrong

Method	Taxable value	Error
Divide by 1.18	₹10,000	correct
Subtract 18%	₹9,676	₹324 too low

That is a 3.2% error on every line of every invoice — enough to make a reconciliation never balance, and enough to misstate input tax credit.

CGST, SGST and IGST

The total tax is the same either way. What changes is the split, and getting it wrong on an invoice is a common filing error.

Intra-state supply — buyer and seller in the same state. The tax divides equally between the centre and the state:


CGST @ 9%	₹900
SGST @ 9%	₹900
Total	₹1,800

Inter-state supply — buyer and seller in different states. A single integrated tax at the full rate:


IGST @ 18%	₹1,800

The place of supply, not your own location, determines which applies. For services delivered remotely this is frequently the recipient’s registered address, which is why it must be captured at invoicing time.

The rate slabs

Rate	Typical goods and services
0%	Fresh produce, milk, unbranded flour, books, education, healthcare
5%	Packaged food, transport, small restaurants, economy air travel
12%	Processed food, business class air travel, some apparel
18%	Most services, electronics, industrial goods
28%	Cars, tobacco, aerated drinks, luxury goods

Rates are set by HSN code for goods and SAC code for services. Look up your specific code on the CBIC portal rather than assuming — the difference between 12% and 18% on a large contract is substantial, and misclassification is your liability, not the buyer’s.

Compensation cess

Some goods in the 28% band attract an additional cess: cars by engine size, tobacco, aerated drinks and coal. It ranges from 1% to over 200% and is not included in this calculator. Add it separately if your product attracts it.

Common mistakes to avoid

Subtracting the percentage to remove GST. As above. This is the single most common GST arithmetic error, and it is always wrong in the same direction — understating the taxable value and therefore the credit you can claim.

Using CGST/SGST on an inter-state invoice. The total collected is identical, but the recipient cannot claim the credit correctly, and both parties end up amending returns.

Charging GST on the pre-discount price. GST applies to the discounted price, provided the discount is on the invoice and was agreed before or at the time of supply. A discount given later can only reduce the taxable value if it was pre-agreed and can be linked to specific invoices.

Rounding each line separately. Round once, at the invoice total. Rounding per line and summing can differ by several rupees from taxing the total, which matters when a system reconciles to the paisa.

Forgetting reverse charge. On certain supplies — goods transport agency services, legal services from an advocate, imports — the recipient pays the GST directly rather than the supplier collecting it.

When registration is required

Generally once turnover exceeds ₹40 lakh for goods or ₹20 lakh for services, with lower thresholds of ₹20 lakh and ₹10 lakh in special category states. Registration is mandatory regardless of turnover for inter-state supply of goods, e-commerce sellers, and anyone liable under reverse charge.

When this calculator is not the right tool

For US sales tax, which is charged once at retail rather than at every stage, use the sales tax calculator. For working out a sale price with stacked discounts before tax is applied, the discount calculator handles the order of operations. And for anything involving input tax credit reconciliation across many invoices, you want accounting software, not a single-value calculator.

GST Calculator