3 Methods to Calculate GST in Australia
Calculating 10% GST in Australia is straightforward once you understand the three main methods. Whether you need to add GST to a price, remove it from a total, or find the GST amount only, here's everything you need to know.
Method 1: Add GST to a Price (GST-Exclusive → GST-Inclusive)
Formula:
Total = Amount × 1.10
Or: Total = Amount + (Amount × 0.10)
Example:
- Product price (excl. GST): $100
- GST amount: $100 × 0.10 = $10
- Total price (incl. GST): $110
Method 2: Remove GST from a Total (GST-Inclusive → GST-Exclusive)
Formula:
Amount = Total ÷ 1.10
GST Amount = Total - (Total ÷ 1.10)
Example:
- Total price (incl. GST): $110
- Amount (excl. GST): $110 ÷ 1.10 = $100
- GST amount: $110 - $100 = $10
Method 3: Calculate GST Amount Only
Formula:
GST Amount = Amount × 0.10
Example:
- Product price: $100
- GST amount: $100 × 0.10 = $10
Quick Reference Table
| Amount (Excl. GST) | GST (10%) | Total (Incl. GST) |
|---|---|---|
| $50 | $5.00 | $55.00 |
| $100 | $10.00 | $110.00 |
| $500 | $50.00 | $550.00 |
| $1,000 | $100.00 | $1,100.00 |
| $5,000 | $500.00 | $5,500.00 |
| $10,000 | $1,000.00 | $11,000.00 |
Common Mistakes to Avoid
❌ Wrong: Multiply by 0.10 to remove GST
If the price is $110 (incl. GST), multiplying by 0.10 gives you $11, not the GST amount.
✅ Correct: Divide by 1.10 first
$110 ÷ 1.10 = $100 (excl. GST), then $110 - $100 = $10 GST
Rounding Rules
The ATO requires that you round GST amounts to the nearest cent. For amounts ending in exactly 0.5 cents, round up to the next cent.
- $10.504 → rounds to $10.50
- $10.505 → rounds to $10.51
- $10.506 → rounds to $10.51
Using a Calculator
For accurate, instant calculations, use our free GST calculator. It handles all the math for you and ensures proper rounding according to ATO requirements.