Percentage Calculator
Calculate percentages three ways: find what percent of a number is, percentage of a total, and percentage increase or decrease between any two values.
A percentage expresses a number as a fraction of 100. The word comes from the Latin “per centum” — meaning “by the hundred.”
The three core percentage formulas:
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Find what percentage A is of B: Percentage = (A / B) × 100
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Find a percentage of a number: Result = (Percentage / 100) × Number
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Find the original number when you know a percentage: Original = Result / (Percentage / 100)
Worked examples:
Example 1 — What percentage is 45 of 180? Percentage = (45 / 180) × 100 = 25%
Example 2 — What is 35% of 240? Result = (35 / 100) × 240 = 84
Example 3 — 60 is 15% of what number? Original = 60 / (15 / 100) = 60 / 0.15 = 400
Common uses:
- Discounts: a 20% off sale on a £150 item saves £30
- Tax: 20% VAT on £80 adds £16
- Test scores: getting 42 out of 56 questions right = 75%
- Interest rates: 5% annual interest on £10,000 = £500/year
- Tip calculation: 15% tip on a £65 bill = £9.75
Percentage vs percentage points: These are different. If interest rates rise from 2% to 3%, that is a 1 percentage point increase — but a 50% increase in the rate itself. This distinction matters in finance and statistics.
Quick mental maths tricks:
- 10% = move decimal one place left (£250 → £25)
- 5% = half of 10%
- 1% = divide by 100
- 25% = divide by 4
- 33% ≈ divide by 3