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Percentage Calculator
Calculation
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How it works
Three formulas:
- X% of Y = (X ÷ 100) × Y
- X is what % of Y = (X ÷ Y) × 100
- % change = ((Y − X) ÷ X) × 100
Worked example
20% of £150 = (20 ÷ 100) × 150 = £30.
£42 is what % of £200? (42 ÷ 200) × 100 = 21%.
£80 → £92 = ((92 − 80) ÷ 80) × 100 = +15%.
Who should use this
- •Shoppers checking discounts and sale prices
- •Anyone working out tips, tax or service charges
- •Investors comparing returns
Common mistakes
- ×Confusing 'percentage' with 'percentage points' — 4% to 6% is +2 percentage points but a +50% change
- ×Calculating change from the wrong base — always divide by the original number
Frequently asked questions
What's the difference between % and percentage points?▾
If a rate goes from 4% to 6%, that's a 2 percentage point rise but a 50% increase.
Why is my answer slightly off?▾
Floating-point arithmetic can show tiny rounding errors. We round to 4 decimal places for display.