GST calculator
Add GST to a net price, or work backwards from a GST-inclusive price, at any rate. It covers India’s CGST/SGST split as well as GST in Australia, New Zealand, Singapore and Canada.
How the GST calculator works
GST (goods and services tax) is charged as a percentage of the price before tax. This calculator does the maths in both directions:
- Add GST: enter the price before GST. The GST and the total including GST are calculated for you.
- Remove GST: enter a GST-inclusive price. The calculator works out the original price and how much of the total is GST.
GST formulas
| To find | Formula |
|---|---|
| GST amount (adding) | price × rate ÷ 100 |
| Total including GST | price × (1 + rate ÷ 100) |
| Price before GST (removing) | total ÷ (1 + rate ÷ 100) |
| GST included in a total | total − total ÷ (1 + rate ÷ 100) |
Example: adding 18% GST
A web designer in India charges 40,000 for a website. GST at 18% is 40,000 × 0.18 = 7,200, so the invoice total is 47,200. For a client in the same state, that is shown as CGST 3,600 + SGST 3,600. For a client in another state, it is IGST 7,200.
Example: removing 10% GST
An Australian customer paid 550 including GST. The price before GST is 550 ÷ 1.10 = 500, and the GST included is 50. (Taking 10% of 550 would give 55, which is wrong.)
Showing GST on an invoice
A GST invoice normally shows your registration number, the price before tax, the GST rate and amount, and the total. In the invoice generator, enable Tax, rename it to “GST” and enter the rate. It is applied after any discount.
Rates and invoice rules change, so check the current requirements with your tax authority, especially for mixed-rate or cross-border sales.
Frequently asked questions
How do I calculate GST on a price?
Multiply the price before GST by the GST rate. For example, 18% GST on 1,000 is 1,000 × 0.18 = 180, so the total is 1,180.
How do I remove GST from a total?
Divide the GST-inclusive total by 1 plus the rate. At 18%, 1,180 ÷ 1.18 = 1,000 before GST. Do not simply subtract 18% of the total, which gives the wrong answer.
What is the difference between CGST, SGST and IGST?
In India, a sale within one state is taxed as CGST (central) plus SGST (state), each at half the total rate. A sale between states is taxed as IGST at the full rate. The total tax is the same either way.
Which GST rate should I use?
It depends on your country and what you sell. Common rates include 10% in Australia, 15% in New Zealand, 9% in Singapore and 5% federal GST in Canada. India uses slabs such as 5% and 18%. Always confirm with your tax authority.