Six Essential Percentage Calculations for Australian Business
1. What is X% of Y? — The Most Common
Formula: Y × (X ÷ 100). Use for calculating discounts, commission, GST estimates, deposit amounts. Example: 20% off $250 = $250 × 0.20 = $50 discount. Final price = $200.
2. X is What % of Y? — Ratios and Proportions
Formula: (X ÷ Y) × 100. Use for profit margin analysis, market share, completion tracking. Example: profit of $30,000 on revenue of $120,000 = (30,000 ÷ 120,000) × 100 = 25% gross margin.
3 & 4. Percentage Change — Growth and Decline
Formula: ((New − Old) ÷ Old) × 100. Essential for year-on-year business comparisons, salary change calculations, property price movements, and performance KPI tracking. Positive result = increase; negative = decrease.
5 & 6. Adding and Removing Percentages — GST Calculations
The most-used functions for Australian GST-registered businesses. To add 10% GST: multiply by 1.10. To remove GST from an inclusive price: divide by 1.10. To find just the GST component in an inclusive price: divide by 11.
| Ex-GST Amount | GST (10%) | Inc-GST Total |
|---|---|---|
| $100 | $10.00 | $110.00 |
| $1,000 | $100.00 | $1,100.00 |
| $10,000 | $1,000.00 | $11,000.00 |