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GST Calculator
Add GST to a price or work out the GST inside a total.
GST calculations come in two directions, and the second one catches people out. Adding GST is straightforward multiplication. Finding the GST already inside a total requires division, and subtracting the percentage instead will give you the wrong answer every time.
The GST formula, both ways
Adding GST: GST = amount × rate ÷ 100, and the total is amount + GST. A price of 2,000 at 18% carries 360 of GST, for a total of 2,360.
Finding the GST in a total: GST = total × rate ÷ (100 + rate). For 2,360 at 18% that is 2,360 × 18 ÷ 118 = 360, leaving 2,000 net. Two shortcuts are worth remembering: at 10% (Australia) the GST is the total divided by 11, and at 15% (New Zealand) it is the total × 3 ÷ 23, so 230 holds 30 of GST.
Both directions
- Enter your amount.
- Enter the GST rate that applies.
- Choose whether the amount is exclusive of GST or already includes it.
- Read the GST amount and the other figure.
- Use the exclusive mode for quoting and the inclusive mode for reconciling receipts.
Extracting GST from a gross amount
If a bill totals 1,180 including 18% GST, the GST is not 18% of 1,180. Divide instead: 1,180 ÷ 1.18 = 1,000 net, so the GST component is 180.
The general rule is gross ÷ (1 + rate) = net. At 10% you divide by 1.1; at 15% by 1.15. Getting this backwards inflates your reported net revenue and understates the tax you owe, which is the kind of error that surfaces at an awkward moment.
Common GST rates
| Country | Standard rate | Divide gross by |
|---|---|---|
| Australia | 10% | 1.10 |
| New Zealand | 15% | 1.15 |
| Canada (federal GST) | 5% | 1.05 |
| Singapore | 9% | 1.09 |
| India (since 22 September 2025) | 5 / 18%, 40% on luxury and sin goods | 1.05 / 1.18 / 1.40 |
Points worth checking locally
- Whether your displayed prices must include GST — consumer rules vary.
- Which rate slab applies to your specific goods or services.
- The registration threshold below which you do not charge GST at all.
- Whether you can claim input credits on business purchases.
- Provincial or state taxes layered on top of a federal rate, as in Canada.
GST questions
How do I add GST to a price?
Multiply the net amount by the rate and divide by 100 for the GST, then add it on. Or multiply by (1 + rate) to get the total directly: 500 at 10% becomes 550.
How do I calculate the GST inside a total?
Divide the gross by (1 + rate) to get the net, then subtract. A total of 550 including 10% GST breaks down as 500 net and 50 GST. Taking 10% off 550 gives 495, which is wrong.
Is GST the same as VAT?
Functionally very similar — both are multi-stage consumption taxes with input credits. The name differs by country, and the detailed rules on rates, exemptions and registration vary considerably.
How do I find the GST amount from a total?
Multiply the total by the rate, then divide by 100 plus the rate. A receipt of 1,150 at 15% holds 1,150 × 15 ÷ 115 = 150 of GST. Subtracting 15% of 1,150 would give 172.50, which overstates the tax.
Which rate should I use?
Whichever applies to your goods or services in your jurisdiction. India in particular uses several slabs depending on the category, so check the classification rather than assuming a single rate.
