GST Calculator
Add GST to a base price or remove GST from a GST-inclusive amount.
How the GST calculator works
This GST calculator works in both directions. Use Add GST when you have a pre-tax figure and need the tax-inclusive price a customer pays. Use Remove GST when you only have the final amount on an invoice and need to work out the base price and the tax hiding inside it — the reverse GST calculation most people search for. Rates are typed in by hand, so the same page works for India's 5 / 12 / 18 / 28 per cent slabs, Australia and New Zealand's flat rate, Singapore, Canada and anywhere else GST or VAT applies.
How to use the GST Calculator
- Pick a mode: Add GST for an exclusive amount, Remove GST for an inclusive total.
- Type the amount you already know into Amount.
- Enter your GST Rate (%) — 18 for India's standard slab, 10 for Australia, 15 for New Zealand.
- Read the exclusive price, the GST portion, and the inclusive total side by side.
Formula and a worked example
Add GST: GST = Amount × r · Inclusive = Amount × (1 + r)
Remove GST: Exclusive = Inclusive ÷ (1 + r) · GST = Inclusive − Exclusive
Here r is the rate written as a decimal, so 18% becomes 0.18. The reverse calculation is the part that trips people up: you cannot simply take 18% of the inclusive total, because that 18% was charged on the smaller base figure, not on the total.
Worked example
An invoice reads ₹56,000 including 18% GST. Dividing gives 56,000 ÷ 1.18 = ₹47,457.63 as the base price, so the GST inside it is ₹8,542.37. Taking 18% of ₹56,000 would have given ₹10,080 — over ₹1,500 too much, which is exactly the mistake the reverse mode prevents.
Frequently asked questions
How do you calculate GST from a total amount?
Divide the total by (1 + rate). At 18%, divide by 1.18 to get the pre-GST price, then subtract that from the total to get the GST. Choose Remove GST above and the calculator does both steps.
How do I calculate the price before GST?
The price before GST is the exclusive amount: inclusive total ÷ (1 + rate). For a ₹11,800 bill at 18%, that is 11,800 ÷ 1.18 = ₹10,000.
Is GST calculated on the base price or the final price?
On the base (exclusive) price. GST is added on top, which is why removing it needs division rather than subtracting a percentage of the total.
Can I use this for VAT?
Yes. VAT works the same way arithmetically — enter your VAT rate in the rate field and both modes behave identically.
Related calculators
Other tools people use alongside the GST calculator.