How GST Works on Australian Tax Invoices
How it works
When a GST-registered business sells goods or services, it must issue a tax invoice that shows the GST component. The invoice can contain a mix of taxable items (10% GST), GST-free items (0% GST, but you can still claim credits on related costs), and input-taxed items (0% GST, and no credits claimable on related costs). Each category is totalled separately, and only the taxable portion attracts GST.
There are two ATO-accepted methods for calculating GST across multiple line items. The per-item method calculates GST on each line individually and rounds to the nearest cent before summing — this is the most precise approach. The total invoice method sums all taxable amounts first, then calculates GST on the total. The difference is usually a few cents, but over thousands of invoices per year it can add up. Most accounting software defaults to the per-item method.
For invoices under $82.50 (including GST), the ATO allows a simplified format — you don't need to show the GST amount separately, just state that the total price includes GST. Above $1,000 (including GST), the invoice must also show the buyer's identity (name or ABN).
When to use this calculator
- You're preparing a tax invoice with mixed GST statuses — some items taxable, some GST-free, some input-taxed — and need to get the totals right
- You want to check whether the per-item or total invoice rounding method produces a different result for your specific invoice
- You're a bookkeeper or accountant reconciling invoices and need to verify that the GST breakdown matches the totals
- You're building a quote or estimate and want to show the client a clear GST-inclusive and GST-exclusive breakdown by category
- You need to confirm your invoice meets the ATO's tax invoice requirements before sending it to a client
Key concepts
- Taxable supply
- A sale where 10% GST applies. The seller collects GST and remits it to the ATO. The buyer (if GST-registered) can claim the GST back as an input tax credit. Most standard goods and services fall into this category.
- GST-free supply
- A sale where no GST is charged, but the seller can still claim input tax credits on costs related to making that sale. Common examples: basic food (fresh fruit, vegetables, bread, milk), most medical services, education, childcare, and exports.
- Input-taxed supply
- A sale where no GST is charged and the seller cannot claim input tax credits on related costs. The main examples are residential rent, financial services (loan interest, bank fees), and sales of existing residential property. This is the least favourable category for sellers because the GST on their costs becomes an embedded expense.
- Per-item vs total invoice rounding
- The per-item method calculates and rounds GST on each line item individually, then sums the results. The total invoice method sums all taxable line items first, then calculates GST once on the total. The ATO accepts both. The difference is typically just cents, but the per-item method avoids compounding rounding errors on invoices with many small line items.
Worked example — Mixed invoice for a catering company
Sarah runs a catering business and issues a tax invoice for a corporate event with a mix of taxable and GST-free items.
| Line item | Amount (ex-GST) | GST status | GST |
|---|---|---|---|
| Canapés & prepared food | $1,200.00 | Taxable | $120.00 |
| Equipment hire (tables & chairs) | $450.00 | Taxable | $45.00 |
| Fresh fruit platters | $320.00 | GST-free | $0.00 |
| Plain milk for coffee station | $28.00 | GST-free | $0.00 |
| Summary | Amount |
|---|---|
| Taxable subtotal (ex-GST) | $1,650.00 |
| GST-free subtotal | $348.00 |
| Total GST | $165.00 |
| Invoice total (inc-GST) | $2,163.00 |
The fresh fruit and plain milk are GST-free under Division 38-3 of the GST Act (basic food), so Sarah charges no GST on those items. The prepared food and equipment hire are taxable at 10%. Sarah's client pays $2,163.00 total, and if they're GST-registered, they can claim the $165.00 GST component as an input tax credit on their next BAS.