Goods and services tax is a broad consumption tax charged as a percentage of the sale price. The rate differs enormously by country and often by product category within a country, so it is an editable input here rather than a fixed figure. India uses a slab system of 5%, 12%, 18% and 28%; Australia, New Zealand, Canada and Singapore all use single national rates at quite different levels.
Adding tax is straightforward multiplication. Removing it is where mistakes happen: to find the net price inside a tax-inclusive total you divide by one plus the rate, you do not subtract the percentage. Taking 18% off a gross figure of 1,180 gives 967.60, which is wrong; dividing by 1.18 gives the correct 1,000.
On the defaults, $1,500 plus 18.0% GST is $1,770.00, with $270.00 of tax. Read the other way, if $1,500 were already tax-inclusive the net price would be $1,271.19 and the tax inside it $228.81. Where GST is split between central and state governments, each takes half — $135.00 here.
The formula
net- Price before tax
gross- Price including tax
rate- GST rate, which varies by country and product
CGST / SGST- The central and state halves where GST is split
How to use this calculator
- Enter the amount you are working from.
- Choose whether that amount already includes GST or not.
- Enter the GST rate that applies — it differs by country and category, so set it yourself.
- The gauge shows the GST amount; the net, gross and split appear below.
Worked examples
Adding 18.0% to $1,500
$1,500 × 0.180 = $270.00, giving a gross price of $1,770.00. Where the tax is shared, central and state each take $135.00. The tax is 15.25% of the gross price, not 18.0% — that percentage is of the net.
Stripping the tax out
If $1,500 already includes 18.0% GST, the net is $1,500 ÷ 1.18 = $1,271.19 and the tax is $228.81. Subtracting 18.0% instead would give $1,230.00, understating the net by $41.19.
How to read your score
Frequently asked questions
What GST rate should I use?
The one for your country and product category. India applies 5%, 12%, 18% or 28% depending on the item; Australia and New Zealand use single national rates; Canada layers provincial tax on top of the federal portion. Check the rate for your specific supply rather than assuming.
What is the difference between GST and VAT?
Almost none in mechanism — both are multi-stage consumption taxes with credit for tax paid on inputs. The name differs by jurisdiction, and some countries operate a dual federal and state structure under the GST label.
What is the reverse charge?
A rule that shifts the obligation to account for the tax from the supplier to the buyer, common on cross-border services. The buyer records both the output and input tax, which usually nets to nothing if they can recover it in full.
Can I reclaim GST on business purchases?
If you are registered and the purchase is for taxable supplies, generally yes, through an input tax credit. That is what makes GST a tax on final consumption rather than on business activity.
Why does my invoice show CGST and SGST separately?
That is the Indian dual structure for supplies within a state — the total rate is split equally between central and state government. Interstate supplies use a single IGST line instead.
GST reference
| Rate | GST on 1,000 | Gross price | Net inside a 1,000 gross |
|---|---|---|---|
| 5% | 50.00 | 1,050.00 | 952.38 |
| 7% | 70.00 | 1,070.00 | 934.58 |
| 10% | 100.00 | 1,100.00 | 909.09 |
| 12% | 120.00 | 1,120.00 | 892.86 |
| 15% | 150.00 | 1,150.00 | 869.57 |
| 18% | 180.00 | 1,180.00 | 847.46 |
| 20% | 200.00 | 1,200.00 | 833.33 |
| 28% | 280.00 | 1,280.00 | 781.25 |
The last column shows why you divide rather than subtract when removing tax from a gross figure.