How to use this GST calculator
- Enter the amount. Type the price you are starting from, e.g. 100. The currency does not matter, the calculator works with the plain number.
- Enter the GST rate. Type the percentage that applies, such as 18 for India's standard slab, or use a quick-pick button for 5, 18, 40 or 10, or the country dropdown for India, Australia, Canada, New Zealand and Singapore rates.
- Pick a mode. Choose "Add GST" when your price is net (before GST) and you want the total, or "Reverse GST" when your price already includes GST and you want to pull the GST back out of it.
- Read the three cards. Net is the price excluding GST, GST amount is the GST portion, and Gross is the full GST-inclusive total. They recalculate instantly as you type.
How GST is added and reversed
GST is a flat percentage applied to a price, so two small formulas cover every case. To add GST to a net price: GST = net × (rate ÷ 100) and gross = net × (1 + rate ÷ 100). With a net of 100 at 18%, that is 100 × 0.18 = 18 GST and a 118 gross.
To reverse GST that is already inside a GST-inclusive price, you cannot simply take the percentage of that total, you have to divide it out: net = inclusive ÷ (1 + rate ÷ 100), then GST = inclusive − net. For an inclusive price of 118 at 18%, that is 118 ÷ 1.18 = 100 net and 18 GST. A common mistake is taking 18% of 118, which overstates the GST, because the 18% was charged on the net 100, not the 118 total.
GST rates differ by country
GST is the same idea everywhere, a flat percentage added to goods and services, but the rate is not. So type the rate that applies where you are, or use the country quick-pick, and this tool handles the rest. Confirmed current rates include:
- India: a simplified structure since September 2025 of mainly 5 percent and 18 percent, with a 40 percent rate for luxury and sin goods (plus a couple of niche rates on a small number of specific items).
- Australia: a single 10 percent rate on most goods and services.
- Canada: a 5 percent federal GST; several provinces combine it with a provincial sales tax into a higher Harmonized Sales Tax, so your local total can be more than 5 percent.
- New Zealand: 15 percent.
- Singapore: 9 percent (raised from 8 percent at the start of 2024).
Malaysia does not currently charge GST, it replaced GST with a Sales and Service Tax (SST) in September 2018 and has kept SST since. The quick-pick buttons cover India's three current slabs plus Australia's 10 percent, and the country dropdown adds Canada, New Zealand and Singapore, but you can type any rate, including decimals, if yours differs. Rates change over time, so double-check the current figure for your country before relying on it for anything official.
Common real-world uses
- Quoting a client: add GST to a net fee so you can show the all-in price.
- Reading a receipt: remove the GST from a gross total to see exactly how much was GST.
- Bookkeeping: split a GST-inclusive expense into its net and GST parts for your records.
- Pricing products: work backwards from a target shelf price to the net amount you actually keep.
Frequently asked questions
How do I add GST to a net price?
Pick "Add GST (net price)", enter the net price and the rate, and the calculator multiplies the price by the rate to get the GST, then adds it on. For example, 18% GST on 100 gives 18 in GST and a 118 gross total.
How do I reverse GST out of a GST-inclusive price?
Choose "Reverse GST (inclusive price)" and enter the GST-inclusive price. The calculator divides by 1 plus the rate to recover the pre-GST net price, then shows the GST that was included. A 118 price at 18% gives a 100 net and 18 of GST.
What GST rate should I use?
It depends on your country. India uses mainly 5 and 18 percent since its September 2025 reform (40 percent for luxury and sin goods), Australia uses 10 percent, Canada charges a 5 percent federal GST, New Zealand 15 percent and Singapore 9 percent. Type whichever rate applies to you, or use the quick-pick buttons or country dropdown.
Does it handle decimal rates?
Yes. Both the amount and the rate accept decimals, so unusual rates and prices like 19.99 work perfectly. Results are rounded to two decimal places for display.
Which currency does it use?
None in particular, it is currency-neutral. Whatever number you enter is treated as a plain amount, so the net, GST and gross all come out in the same currency you typed.
Why can I not just take the percentage off a gross price to remove GST?
Because the GST was charged on the net price, not the gross. Taking 18% of a 118 gross gives about 21.24, which overstates the GST. The correct method divides the gross by 1.18 to get the 100 net, leaving 18 of GST.
Is the calculator private?
Yes. Every calculation runs with JavaScript. The amounts and rates you enter are never uploaded or sent anywhere.
Results are rounded for display; for invoices, filings or accounting, double-check critical figures against official GST rates.