GST Calculator

Tax added = price before tax × rate | Tax removed = GST inclusive price ÷ (1 + rate) − GST inclusive price

baseAmount

The amount the tax is worked out from, and which amount that is depends on the direction you chose. Removing tax, it is the GST inclusive price, the one on the label. Adding tax, it is the price before tax. The field is named for the quantity rather than for either price because a name like net amount would be wrong in half the settings — and mixing the two up is the most common GST error there is, since adding tax to a price that already contains it charges the tax twice.

gstRate

The rate to add or remove, as a percentage. It is a field rather than a fixed list because there is no single rate to fix: 10% in Australia, 15% in New Zealand, 9% in Singapore, and 5% federally in Canada before any provincial tax is added on top. A GST rate is normally one standard figure for a whole country rather than a set of bands, which is the structural difference from value added tax — what varies is not the rate but the list of supplies that are zero-rated or exempt, and that list is a question of tax law rather than of arithmetic.

mode

Which direction to go. Remove tax takes a price that already includes it and takes the tax out, and that is the default here because Australia, New Zealand and Singapore all require prices shown to consumers to include GST, so the number in front of you is the one with tax inside it. Add tax takes a price that does not include it and puts the tax on top, which is what you want when you are the seller quoting a net figure. Both are ordinary, and neither is a special case of the other.

taxAmount

The tax itself, and the panel's main figure because that is what the page is asked for. In both directions it is the difference between the two prices, and in the removal direction it is worked out by subtracting rather than by dividing a second time — which is why the pair of prices and the tax always add up exactly, with no rounding gap left behind for anyone to chase.

netAmount

The price with the tax taken out: the taxable turnover, and the figure that GST is actually charged on. When you removed tax, this is what the division produced; when you added it, this is what you typed. It is the number that belongs on a business activity statement, and the one a margin calculation has to use if the margin is to mean anything, since a revenue line that includes tax over a cost line that does not is mixing two different things.

grossAmount

The price with the tax in it: what the customer actually pays and what lands in the till. When you removed tax, this is what you typed; when you added it, this is the sum. It is the number that reconciles against a bank statement, and it is not the taxable turnover.

gstFraction

The tax as a share of the GST inclusive price, and the row that surprises people. At a rate of 10% it is 9.09%, at 15% it is 13.04%, and at 9% it is 8.26% — never the rate itself, because the rate is a share of the price before tax and this figure is a share of a larger number. It is the fraction to set aside out of money already received, and it is why a rate of 10% is sometimes described as one eleventh of a tax-inclusive price.

Use it when you have a price in one form and need it in the other: a shelf price includes GST and you need the amount to set aside, a supplier quotes a figure before tax and you need the total to pay, a receipt arrived with only a tax-inclusive total and the return asks for the turnover excluding it. Use remove GST to work backwards from a price a customer paid, and add GST when you are the one quoting. The removal direction has a second use that is easy to miss — checking whether an invoice was worked out correctly, because dividing the inclusive total by one plus the rate is a sum anyone can redo, and a supplier who subtracted the percentage instead will be several percent out. And the last row answers a question the other three do not: how much of the money already in the till is not yours. That is the figure to set aside, and it is smaller than the rate, which is exactly why businesses that set aside the rate itself come up short.

1. The default: 110 including 10%

   1. Net price: 110 ÷ 1.10 = 100
   2. Tax: 110 − 100 = 10
   3. Tax as a share of the inclusive price: 10 ÷ 110 × 100 = 9.09%

   The direction that matches how prices are displayed in Australia, New Zealand and Singapore, and the one where the last row is most worth reading: 10% of the price before tax is 9.09% of the price the customer pays, because the 10 is being measured against a total that already contains it. Both statements are true of the same 10.

2. The same numbers from the other end: 100 before 10%

   1. Tax: 100 × 10 ÷ 100 = 10
   2. Inclusive price: 100 + 10 = 110
   3. Tax as a share of the inclusive price: 10 ÷ 110 × 100 = 9.09%

   All four figures are identical to the example above, which is the point: when the rate divides out cleanly the two directions are inverses of each other, and the page can be used from either end. The division is not decoration. Subtracting 10% of 110, which is 11, would give 99 and a tax of 11 — a net price that is too low, a tax that is too high, and a return that will not reconcile.

3. New Zealand, 15%: 230 including tax

   1. Net price: 230 ÷ 1.15 = 200
   2. Tax: 230 − 200 = 30
   3. Tax as a share of the inclusive price: 30 ÷ 230 × 100 = 13.04%

   New Zealand's rate is 15%, higher than Australia's, and the last row moves with it: a 15% tax is 13.04% of an inclusive price. Note how far apart the two percentages look on the same 230 — this is why a business that sets aside 15% of its takings puts aside more than it owes, while one that thinks a 10% rate means a tenth of the till keeps too little.

4. Singapore, 9%: 40 before tax

   1. Tax: 40 × 9 ÷ 100 = 3.60
   2. Inclusive price: 40 + 3.60 = 43.60
   3. Tax as a share of the inclusive price: 3.60 ÷ 43.60 × 100 = 8.26%

   Singapore's rate has moved several times in recent years, which is the reason the rate is a field rather than a fixed list on this page — a calculator that hard-coded a rate would be wrong within a couple of budgets. Enter whatever rate is in force and the three prices close on each other exactly.

5. A rate that does not close: 99.99 before 9%

   1. Tax: 99.99 × 9 ÷ 100 = 8.9991, rounded to 9.00
   2. Inclusive price: 99.99 + 9.00 = 108.99
   3. Tax as a share of the inclusive price: 9.00 ÷ 108.99 × 100 = 8.26%

   Enter 108.99 with the same rate and the removal direction gives back 99.99 and a tax of 9.00 — the pair closes, even though 8.9991 had to be rounded to get there. It closes because the tax is defined as the difference between the two prices rather than computed a second time, so the rounding lands in one place and stays there instead of drifting between the three rows.

6. A zero rate: 110 at 0%

   1. Net price: 110 ÷ 1.00 = 110
   2. Tax: 110 − 110 = 0
   3. Tax as a share of the inclusive price: 0 ÷ 110 × 100 = 0%

   Not a degenerate case to be filtered out but a real category: New Zealand zero-rates most food, Singapore zero-rates exports and international services, and Australia has a list of GST-free supplies including most basic food, health and education. A zero rate is not the same thing as being outside the tax — a zero-rated seller can usually still claim back the GST on its inputs, which is precisely the difference between zero-rated and exempt.

This calculator does the arithmetic and nothing else. It does not know which rate applies to what you are selling, and that is not a detail it is leaving out for brevity: whether a supply is zero-rated, exempt or taxable at the standard rate is a question about the nature of the transaction, answered by tax law and by the practice of the authority that administers it, and no arithmetic can decide it. It also does not know whether you are registered at all — a business below the registration threshold in the table below does not charge GST and generally cannot claim it back, which means the field above is answering a question that does not yet apply to it. Nor does it model anything beyond the tax itself: no input tax credits, no adjustment for a change in the rate, no cross-border or place-of-supply rules, no reverse charge, no margin scheme, no second-hand goods rules, and no rounding rule imposed by an administration, some of which require the tax to be rounded down rather than to the nearest cent. Canada needs a word of its own here, because the table gives one federal figure and the tax a Canadian customer actually pays is that figure plus a provincial part that differs by province and is administered differently in Quebec — so the 5% row is the federal goods and services tax only, and a real Canadian receipt will rarely show 5%. Two things about the arithmetic are worth expecting rather than reporting. The first is the gap that appears when the rate does not divide cleanly: the removal direction can produce a price before tax with more decimals than a price would ever have, and it is rounded here to the nearest cent, which means the tax on a receipt will occasionally differ by a cent from the tax on a return worked out in one step. The second is that the last row is a fraction of an inclusive amount and not a rate, so it will never equal the rate you entered — 10% becomes 9.09%, 15% becomes 13.04%, 9% becomes 8.26%. Finally, the rates and thresholds in the table are the ones in force at the time of writing in the places named. Rates change, usually in a budget, and thresholds are reviewed too; check the current figure with the tax authority before deciding whether you need to register, because that decision is the one with penalties attached.

How do I remove GST from a price that includes it?

Divide by one plus the rate, then subtract to get the tax. At 10%, an inclusive price of 110 gives a price before tax of 110 ÷ 1.10 = 100 and a tax of 10. Subtracting 10% of 110 instead gives 99, which is wrong — the 10% was charged on the smaller number, so taking 10% off the larger one takes off too much.

Why is the tax 9.09% of the price and not 10%?

Because the two percentages are measured against different totals. The rate of 10% is a share of the price before tax; the 9.09% is the same tax measured against the inclusive price, which is 10% larger. Both describe the same 10. The general rule is that a rate of r corresponds to r ÷ (1 + r) of the inclusive price, so 10% becomes 9.09%, 15% becomes 13.04% and 9% becomes 8.26%.

What is a GST inclusive price?

The price a customer actually pays, with the tax already inside it. Australia, New Zealand and Singapore all require prices displayed to consumers to include GST, so in those countries a price on a shelf or in an advertisement is inclusive by law, and the tax has to be divided out of it rather than added to it. That is why the removal direction is the default on this page.

What is the registration threshold, and does it apply to me?

The turnover below which a business is not required to register and therefore does not charge GST at all. It is $75,000 in Australia, $60,000 of taxable supplies in any 12 months in New Zealand, S$1 million in Singapore and $30,000 in Canada. Below the threshold the calculus is a choice rather than an obligation in some jurisdictions, and registering voluntarily means charging tax to your customers — so check with the authority before deciding.

Which GST rate should I use?

The one the tax authority where you are selling says applies to what you are selling, and the calculator cannot tell you which that is. The table below gives the standard rates in four countries — 10% in Australia, 15% in New Zealand, 9% in Singapore and 5% federally in Canada — but a GST rate is normally a single national figure, so the harder question is not which rate applies but whether your supply is zero-rated, exempt or taxed at the standard rate at all.

Is a zero rate the same as being exempt?

No, and the difference matters. A zero-rated sale is still a taxable sale charged at 0%, so the seller can normally claim back the GST paid on its own inputs; an exempt sale is outside the scope of the tax, and the input tax is usually not recoverable. That is why categories such as most basic food are zero-rated in Australia and New Zealand rather than exempted. Either way the arithmetic on this page gives a tax of nothing and an inclusive price equal to the price before tax.

• A New Tax System (Goods and Services Tax) Act 1999 — the Act that sets the 10% rate and the registration turnover threshold of $75,000, below which a business is not required to register and does not charge GST on its sales — Federal Register of Legislation (Australia)
• GST — the rate of 15%, the registration threshold of $60,000 of taxable supplies in any 12-month period, and the treatment of zero-rated supplies such as exported goods and services — Inland Revenue Department (New Zealand)
• GST — the current rate of 9%, the registration threshold of S$1 million in taxable turnover, and the zero-rate and exemption rules that take some supplies outside the standard rate — Inland Revenue Authority of Singapore (Singapore)
• Excise Tax Act, sections 165 and 148 — the federal goods and services tax at 5% of the value of the consideration, and the small supplier threshold of $30,000 below which registration is not required — Department of Justice, laws-lois.justice.gc.ca (Canada)