GST Calculator

Switch between adding GST to a net price and pulling it back out of a GST-inclusive total. Enter the amount, set the rate that applies in your country — 10% is preloaded to match Australia — and the calculator returns three figures together: the net amount, the GST portion and the gross total, all updating as you type. Read the highlighted total as the number that changes hands at the till; the net and GST lines beneath it show how that total splits. Nothing leaves your browser.

Where the goods and services tax came from

A GST is a value-added tax under another name. The mechanism was invented in France, where the tax official Maurice Lauré (1917–2001), a deputy director of the French revenue service, designed the taxe sur la valeur ajoutée and had it written into law on 10 April 1954. It started narrowly — at first little more than a production tax with a limited right to deduct — and was widened across goods, services and retail trade over the following decade. The underlying idea, taxing only the value each business adds rather than the full sale price every time goods change hands, had been discussed in Germany and the United States in the years after the First World War, but France was the first country to build a working national tax around it.

Lauré's target was the taxe en cascade, a turnover tax charged on the full price at every step from raw material to shop counter, so that tax piled on tax and long supply chains were punished more heavily than short ones. A value-added tax instead charges each business on its sales but lets it reclaim the tax it already paid on its purchases, so the levy bites only on the margin that business adds. Collection is spread across the whole chain, yet the economic weight settles once, on the final consumer, who cannot reclaim anything. The design spread through the European Economic Community after its first two VAT directives of April 1967 required every member state to scrap its cascading turnover tax, and the rules were harmonised further by the Sixth VAT Directive of 17 May 1977. More than 170 countries now run some version of it.

The "goods and services tax" name belongs mainly to Commonwealth countries. New Zealand was the one that turned GST into shorthand for a clean, broad tax: it came into force on 1 October 1986 at 10%, under finance minister Roger Douglas, with a single rate applied to almost everything and very few exemptions. That broad-base, low-exemption structure became the model other governments studied. New Zealand's rate later rose to 12.5% in 1989 and to 15% in 2010. Canada brought in a 7% GST on 1 January 1991 under Brian Mulroney; Singapore introduced a 3% GST on 1 April 1994; and Australia adopted a 10% GST on 1 July 2000 through the A New Tax System legislation of the Howard government, sweeping away the old wholesale sales tax and several state levies.

The two directions of the calculation

Adding GST is a plain percentage increase:

gross = net × (1 + r ÷ 100)

Removing it requires division, not subtraction:

net = gross ÷ (1 + r ÷ 100)

With the defaults — adding 10% to 500 — the GST is 500 × 0.10 = 50 and the gross total is 550. Flip the direction to remove with the same numbers and 500 becomes the inclusive amount: the net is 500 ÷ 1.1 = 454.55 and the GST is the remaining 45.45. The GST is deliberately not 50 here, because in an inclusive price the tax was charged on the smaller net figure, not on the 500 you can see.

Why you divide instead of subtracting a percentage

The most common GST mistake is stripping the tax out by taking the rate straight off the total. It fails because GST is calculated on the net amount, never on the gross one. If gross = net × 1.1, the tax buried in the total is gross − gross ÷ 1.1, which reduces to gross × 0.1 ÷ 1.1 — the total divided by 11, not by 10. That is exactly the Australian Taxation Office's published shortcut: to find the GST inside a tax-inclusive price, divide by 11. A 550 receipt divided by 11 gives 50 of GST and leaves 500 net.

The same algebra hands New Zealand Inland Revenue its rule at 15%. The tax fraction of a GST-inclusive price is 15 ÷ 115, which cancels to 3 ÷ 23 — hence "multiply by 3, divide by 23". On a 115 purchase that isolates exactly 15 of GST. Subtracting 15% instead would take 15% of 115, or 17.25, overstating the tax by 2.25. The error grows as the rate climbs, which is why every tax authority prescribes division and why this calculator never subtracts to reverse a rate. More generally, the tax fraction of any inclusive price is r ÷ (100 + r): 10 in 110, 9 in 109, 5 in 105. Multiply the gross by that fraction to get the GST, and the rest is net.

GST rates that matter in practice

Canada needs a moment of care. The 5% federal GST is only part of the story in most provinces. Ontario and the four Atlantic provinces fold both levels into a single HST: 13% in Ontario, 14% in Nova Scotia since 1 April 2025, and 15% in New Brunswick, Newfoundland and Labrador and Prince Edward Island. British Columbia, Saskatchewan and Manitoba charge a separate provincial sales tax alongside the GST, and Quebec runs its own 9.975% QST the same way. Alberta and the three territories charge the 5% alone. Enter the combined rate from your receipt if you want the full tax picture, or 5% to isolate the federal portion.

What the calculator assumes

One flat rate applies to the whole amount, and no tax compounds on another — a safe assumption in every GST country today, since even Quebec stopped calculating its QST on a GST-inclusive base back in 2013. Full precision is carried internally and figures are rounded only for display, so the net and GST you see always add back to the gross. Zero-rated and exempt items — basic food in Australia, most groceries in Canada, financial services almost everywhere — carry no GST at all, so there is nothing to add or remove for them. And because registered businesses reclaim the GST on what they buy, the figures here describe the tax on a single transaction, not the net amount any one business finally remits to the revenue.

Rates change and registration thresholds differ by country and turnover, so confirm figures with your tax authority or an accountant before invoicing or filing. See the site disclaimer.

Frequently asked questions

How do I remove GST from a total in Australia?

Divide the GST-inclusive amount by 1.1, or use the ATO shortcut of dividing by 11 to get the GST portion directly. A 550 receipt contains 500 net and 50 GST. Subtracting 10% instead would give 495, which is wrong by 5.

What is the GST rate in New Zealand?

15%, unchanged since October 2010 when it rose from 12.5%. To pull GST out of an inclusive price, Inland Revenue's method is to multiply by 3 and divide by 23 — on a 115 purchase that isolates exactly 15 of GST.

Is Canadian GST the same as HST?

Not quite. The federal GST is 5% everywhere in Canada. Ontario and the Atlantic provinces merge it with their provincial share into a single HST of 13% or 15%, while British Columbia, Saskatchewan and Manitoba charge a separate PST on top and Alberta charges nothing beyond the 5%.

What is the GST rate in Singapore?

9% since 1 January 2024. It was 8% during 2023 and 7% for the fifteen years before that, so older receipts and invoices need the rate that applied on their date, not today's.

Why can I not just subtract the percentage to remove GST?

Because GST is charged on the net figure, not the gross one. At 15%, taking 15% off a 115 total gives 97.75 instead of the correct 100, overstating the tax by 2.25. The error grows with the rate, which is why every tax authority prescribes division.