GST Calculator

About this calculator

GST is calculated differently depending on which figure you start from. If you have a price before tax, GST is added on top. If you have a shelf price that already includes tax, the GST has to be extracted from inside it — and taking 18% off a GST-inclusive price is the most common mistake people make, because it gives the wrong answer.

This calculator handles both directions and shows the CGST and SGST split you need for an invoice on a sale within your own state.

How to use this calculator

1. Enter the amount you have.
2. Enter the GST rate that applies to the product. Most mobile, computer and car accessories are taxed at 18%.
3. Choose whether your amount is before GST or including GST.
4. Read the GST amount, along with the base and total values and the CGST/SGST split.

The formula

Adding GST to a price that excludes it:

GST amount = Amount x Rate / 100
Total      = Amount + GST amount

Extracting GST from a price that already includes it:

Base amount = Amount x 100 / (100 + Rate)
GST amount  = Amount - Base amount

The second formula is the one people get wrong. On a GST-inclusive price of ₹1,180 at 18%, the GST is not ₹212.40 (18% of 1,180). It is ₹180, because the tax was calculated on the base of ₹1,000, not on the inclusive total.

For a sale within your own state the GST is split evenly into CGST and SGST. For a sale to another state the whole amount is IGST instead — the total is the same either way.

Worked example

Adding GST. You sell a phone case for ₹1,000 before tax, at 18%.

GST   = 1,000 x 18 / 100 = 180
Total = 1,000 + 180      = 1,180

Extracting GST. The same case is listed at ₹1,180 including tax.

Base = 1,180 x 100 / 118 = 1,000
GST  = 1,180 - 1,000     = 180

Both give ₹180 of GST, split as ₹90 CGST and ₹90 SGST on an in-state sale.

Notes and limits

• GST rates are set by the GST Council and change from time to time. Confirm the current rate for your HSN code before relying on a figure.
• The CGST/SGST split shown here applies to sales within your own state. Interstate sales use IGST at the full rate.
• This calculator does not handle cess, reverse charge, or composition-scheme rates.
• Marketplace fees are themselves taxed. To work out what you actually receive after a marketplace deducts its commission, use the profit margin and selling price calculators alongside this one.

What this calculation assumes

• A single GST rate applies to the whole amount.
• CGST and SGST are split evenly, which is the standard for an in-state supply.
• Cess, reverse charge and composition-scheme rates are not included.