How to calculate reverse GST
Goods and Services Tax (GST) is a comprehensive value-added consumption tax applied to sales of goods and services in Australia, India, Singapore, New Zealand, and Canada. Because commercial invoices display GST-inclusive pricing, business owners and accounting professionals require an accurate reverse GST calculator to calculate pre-GST subtotals and claim input tax credits.
Australian ATO 10% GST rule (Divide by 11)
In Australia, the Australian Taxation Office (ATO) imposes a 10% GST. The official ATO shortcut to determine GST from a tax-inclusive bill is:
For example, for a tax invoice of $550.00 AUD:
- GST Paid = $550.00 ÷ 11 = $50.00 AUD
- Pre-GST Net Price = $550.00 ÷ 1.10 = $500.00 AUD
India GST Slabs (18% & 28%)
India uses a four-tier GST rate structure (5%, 12%, 18%, and 28%). For standard commercial transactions taxed at 18% GST:
Singapore 9% GST (IRAS)
Under the Inland Revenue Authority of Singapore (IRAS), the standard GST rate is 9%:
Global GST Rates & Formulas Comparison Table
| Country / Tax Authority | Standard Rate | Reverse Divisor | Quick Formula |
|---|---|---|---|
| Australia (ATO) | 10% | 1.10 | Divide Gross by 11 |
| India (GST Slabs) | 5% / 12% / 18% / 28% | 1.18 (for 18%) | Gross ÷ 1.18 |
| Singapore (IRAS) | 9% | 1.09 | Gross ÷ 1.09 |
| New Zealand (IRD) | 15% | 1.15 | Multiply Gross by 3/23 |
| Canada (Federal GST) | 5% | 1.05 | Gross ÷ 1.05 |