GST Calculator

What is the GST Calculator?

Goods and Services Tax is a consumption tax added to the price of most goods and services. Prices are quoted either exclusive of GST (tax added at the till) or inclusive (tax already contained in the figure shown).

Extracting GST from an inclusive price is where people most often go wrong. You cannot simply take 18% of the total.

How to use the GST Calculator

1. Enter the amount you are working with.
2. Choose the applicable GST rate.
3. Select Add GST if your figure excludes tax, or Remove GST if it already includes it.

Formula

The reverse calculation divides rather than subtracts. Taking 18% off a ₹1,180 inclusive price gives ₹967.60, which is wrong. Dividing by 1.18 gives ₹1,000, which is right. The difference exists because the 18% was applied to the smaller base, not to the total.

How the calculation works

When adding, the rate applies to the taxable value directly. When removing, the inclusive amount represents 100% + the rate, so dividing by that factor recovers the original 100%.

For supplies within a single state, GST splits equally into Central GST and State GST. For inter-state supplies it is charged as a single IGST at the full rate.

Worked example

Adding: a service priced at ₹1,000 with 18% GST → GST of ₹180, total ₹1,180, split as ₹90 CGST + ₹90 SGST.

Removing: an invoice showing ₹1,180 inclusive of 18% GST → ₹1,180 ÷ 1.18 = ₹1,000 taxable value, so the GST component is ₹180. The round trip confirms both directions agree.

Uses and benefits

• Raise invoices with the correct taxable value and tax split.
• Work out the pre-tax cost of something you have already paid for.
• Separate the CGST and SGST components for filing.