Here is how to add GST to an invoice: multiply each taxable line, or the taxable subtotal, by your country's rate, show that amount as its own GST line, then add it to get the total. To find the GST already inside a price, multiply by the rate over 100 plus the rate, so one eleventh in Australia at 10%.
The two GST calculations you need
There are only two sums. To add GST, multiply the price before tax by the rate and add the result. To find the GST inside a price that already includes it, multiply that price by the rate divided by 100 plus the rate. Everything else on a GST invoice is about showing those figures clearly, line by line and in total.
| Country | Rate | Add GST: multiply the price by | GST inside an inclusive price |
|---|---|---|---|
| Australia | 10% | 1.10 | Price × 1/11 |
| New Zealand | 15% | 1.15 | Price × 3/23 |
| Singapore | 9% | 1.09 | Price × 9/109 |
| India (18% slab) | 18% | 1.18 | Price × 18/118 |
| Canada, Ontario HST | 13% | 1.13 | Price × 13/113 |
| Canada, GST only | 5% | 1.05 | Price × 1/21 |
The fractions come straight from the rate: 15 over 115 reduces to 3 over 23, and 5 over 105 reduces to 1 over 21. The GST invoice generator does these sums for you, with tax added, included or none, and a rate on each line.
What the GST lines look like on the invoice
Put the tax under the line items, never hidden inside them. A clear GST invoice shows a subtotal before tax, one GST line per rate with the rate in brackets, and the total payable. When your prices already include GST, show the total and a line stating how much GST it contains, so the customer can still claim it.
| Prices entered as | Totals block on the invoice (Australian example) |
|---|---|
| GST added | Subtotal $1,240.00; GST (10%) $124.00; Total $1,364.00 |
| GST included | Total $1,529.00; includes GST (10%) of $139.00 |
| No GST (not registered) | Total $1,240.00, with no GST line and no tax invoice title |
Keep the same wording on every invoice you send. A customer’s accounts team will often type the GST figure into their own system, and a consistent layout means they find it in the same place every time.
How to add GST to an invoice in Australia
Australian GST is 10% on most goods and services, and business.gov.au describes it as one eleventh of the sale price. Multiply the GST exclusive amount by 0.10 to get the GST, or divide a GST inclusive price by 11. A registered business must give a tax invoice for taxable sales over $82.50 including GST, or whenever the customer asks.
Adding GST. A bookkeeper bills $1,240.00 for a month of work. GST is $1,240.00 × 0.10 = $124.00, so the invoice total is $1,364.00.
Working back from an inclusive price. A printer quotes $1,529.00 including GST. GST is $1,529.00 ÷ 11 = $139.00, and the price before GST is $1,390.00. Check: $1,390.00 × 0.10 = $139.00.
A figure that needs rounding. A $95.00 inclusive service gives $95.00 ÷ 11 = $8.6363…, which rounds to $8.64 of GST and $86.36 before GST.
The tax invoice must say “tax invoice” and show your ABN, the date, what you sold with quantity and price, and the GST payable; sales over $1,000 also need the buyer’s identity or ABN. You must register once GST turnover reaches $75,000. The Australian tax invoice template and the Australian preset are set up for this.
New Zealand: 15% GST
New Zealand GST is 15%, with some supplies charged at 0%. Multiply the GST exclusive price by 0.15, or find the GST in an inclusive price by multiplying by 3/23. For supplies over $200, show the GST exclusive amount, the GST and the inclusive total, or, when every item is standard rated, the inclusive total and a statement that it includes GST.
Adding GST. A landscaping job is $2,360.00 before GST. GST is $2,360.00 × 0.15 = $354.00, and the total is $2,714.00.
Working back. A $690.00 GST inclusive repair contains $690.00 × 3 ÷ 23 = $90.00 of GST, leaving $600.00 before GST. Check: $600.00 × 0.15 = $90.00.
Inland Revenue now calls the required details “taxable supply information” rather than a tax invoice, but you may keep using a single document titled tax invoice. Over $200 it needs your GST number, which is the same as your IRD number. Registration is required once turnover reaches $60,000 in 12 months. Try the New Zealand preset.
Singapore: 9% GST
Singapore GST is 9% on sales in Singapore unless they are zero rated or exempt. Multiply the price before GST by 0.09 to get the GST, or multiply a GST inclusive price by 9/109 to find the GST inside it. IRAS allows the total GST to be rounded to the nearest cent, worked per item or on the subtotal, as long as you are consistent.
Adding GST. A consultancy bills S$4,850.00. GST is S$4,850.00 × 0.09 = S$436.50, so the total is S$5,286.50.
Working back. A S$218.00 inclusive training session contains S$218.00 × 9 ÷ 109 = S$18.00 of GST, so the price before GST is S$200.00.
A mixed invoice. A standard rated line of S$1,200.00 carries S$108.00 of GST; a zero rated line of S$800.00 carries none and should state that GST is charged at 0%. Subtotal S$2,000.00, GST S$108.00, total S$2,108.00.
A full tax invoice must show “Tax Invoice” prominently, the GST rate, the total before GST, the GST amount and the total including GST. A simplified tax invoice is allowed when the total including GST is S$1,000 or less. The Singapore preset uses 9%.
India: GST slabs, CGST and SGST or IGST
India’s main GST rates since 22 September 2025 are 5% and 18%, with 40% for a few select goods and special rates of 3%, 0.25% and 1.5%. Which tax you charge depends on where the buyer is. A sale within one State carries CGST plus SGST, or UTGST in a Union territory; a sale between States carries IGST.
Inter State sale, 18% slab. A supply in the 18% slab worth Rs 42,500, sold from Karnataka to a buyer in Maharashtra, carries IGST of Rs 42,500 × 0.18 = Rs 7,650, for a total of Rs 50,150.
Inter State sale, 5% slab. Goods in the 5% slab worth Rs 12,800 carry IGST of Rs 640, for a total of Rs 13,440.
Intra State sale. Both CGST and SGST are charged on the same taxable value, each at the rate notified for that item, and each gets its own line with its rate and amount. For example, if the central and State rates for an item were 9% each, Rs 42,500 would carry CGST of Rs 3,825 and SGST of Rs 3,825. Always confirm the rates for your item in the current rate notifications.
Under Rule 46 the invoice must show your GSTIN, the HSN code for goods or the accounting code for services, the taxable value, the rate and amount of each tax, and the place of supply with State name for inter State supplies. Start from the India preset, which handles CGST plus SGST or IGST.
Canada: GST or HST by province
In Canada you charge either 5% GST or a single HST rate, depending on the province or territory where the supply is made under the CRA’s place of supply rules. Multiply the price by the rate and show the tax as a separate amount, or state that the total includes GST/HST. With HST, show the combined rate, not the federal and provincial parts.
| Province or territory | Rate |
|---|---|
| Alberta, British Columbia, Manitoba, Quebec, Saskatchewan, the three territories | 5% GST |
| Ontario | 13% HST |
| Nova Scotia | 14% HST (since 1 April 2025) |
| New Brunswick, Newfoundland and Labrador, Prince Edward Island | 15% HST |
Worked figures. A $3,100.00 job in Ontario carries $403.00 of HST, total $3,503.00. The same job in Alberta carries $155.00 of GST, total $3,255.00. An $860.00 job in Nova Scotia carries $120.40 of HST, total $980.40. A $565.00 Ontario price that includes HST contains $565.00 × 13 ÷ 113 = $65.00 of HST.
British Columbia, Saskatchewan and Manitoba also have provincial sales taxes, and Quebec has QST, run separately from GST/HST. The Canadian invoice template and the Canada preset let you pick GST or HST by province.
Rounding and checking your GST figures
Work in exact cents, round each GST figure once, and check that the amount before tax plus the GST equals the total. Decide whether you calculate GST per line or on the subtotal, then keep to it, because the two methods can differ by a cent on long invoices. IRAS states this consistency rule for Singapore, and it is a sound habit everywhere.
- Check the inclusive sum backwards. If $1,529.00 includes $139.00 of GST, then $1,390.00 × 1.10 should give $1,529.00. It does.
- Do not apply the rate to an inclusive price. 10% of $1,529.00 is $152.90, which is not the GST in that price. It is an easy slip when you are working fast.
- Discounts come first. Take any discount off the line or subtotal, then calculate GST on what the customer actually pays.
- Show the currency. Singapore requires invoices in a foreign currency to convert the amount before GST, the GST and the total into Singapore dollars.
For what else a tax invoice needs, see what a tax invoice is. Billing in the UK, Ireland, South Africa or the UAE instead? Read adding VAT to an invoice, and for American customers, sales tax on US invoices.
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