Whether you are a shopkeeper, a freelancer or just checking a bill, working out GST by hand is error-prone. A free online GST calculator gives you the exact tax amount and the final price in one step, both ways round.

What GST is

Goods and Services Tax (GST) is a single indirect tax applied to the supply of goods and services. In India the common slabs are 5%, 12%, 18% and 28%, with some essentials taxed at 0%. The rate depends on the product or service category.

GST-exclusive vs GST-inclusive — the difference

  • Exclusive: a price quoted before tax. You add GST on top to get the final amount.
  • Inclusive: a price that already contains GST. To find the tax portion you work backwards.

The formulas

Adding GST to a base price:

GST amount = base price × (rate ÷ 100)

Final price = base price + GST amount.

Removing GST from an inclusive price:

Base price = inclusive price × 100 ÷ (100 + rate)

Step-by-step: calculate GST online

  1. Open the free GST Calculator.
  2. Enter the amount.
  3. Pick the GST rate (5, 12, 18 or 28%).
  4. Choose whether the amount is GST-exclusive or GST-inclusive.
  5. Read the base price, the GST amount and the total instantly.

A quick worked example

Say a service costs ₹1,000 and GST is 18%. The tax is 1,000 × 0.18 = 180, so the final price is 1,180. If instead the bill already reads 1,180 inclusive, the base price is 1,180 × 100 ÷ 118 = 1,000 and the tax is 180.

Tips to avoid common mistakes

  • Always confirm whether a quoted price is inclusive or exclusive.
  • Keep the rate consistent across line items; mixed rates confuse totals.
  • For percentages of any kind, the Percentage Calculator is handy.
  • Double-check large invoices — one wrong rate compounds across a whole order.

Frequently asked questions

How do I reverse-calculate GST?

Divide the inclusive price by (100 + rate) and multiply by 100 to get the base amount, then subtract it from the total to find the tax.

Which GST rate applies to my product?

Rates depend on the goods or services category. The calculator lets you try any rate to see the effect.

Is the GST calculator free?

Yes, it is completely free with no signup and runs instantly in your browser.

Final thoughts

GST maths is simple once you know which way round you are working. Get instant, accurate figures with the free GST Calculator and browse the rest of our online calculators.