This percentage calculator handles the everyday percentage questions: what is X% of a number, what percentage one number is of another, and the percentage increase or decrease between two values. It is useful for pricing, discounts, markups, tips, tax, and comparing measurements.
The three percentage questions
Most percentage problems are one of three types. 'What is 15% of 80?' multiplies: 80 × 0.15 = 12. 'What percentage is 12 of 80?' divides and scales: (12 ÷ 80) × 100 = 15%. 'What is the percentage change from 80 to 92?' uses the difference over the original: ((92 − 80) ÷ 80) × 100 = 15% increase. Recognising which type you have is half the battle, and the calculator lays each one out separately.
A percentage is simply a fraction out of 100, so 25% means 25/100 or 0.25. Converting a percentage to a decimal (divide by 100) before multiplying is the reliable way to avoid mistakes.
Common real-world uses
Percentages turn up everywhere: adding sales tax or VAT, taking a discount off a list price, calculating a tip, working out a profit margin, or expressing how much a material expanded or contracted. Percentage change in particular is the one people get wrong most often, because it must always be measured against the original (starting) value, not the new one.
A tool listed at £120 is on sale for £90. What is the percentage discount?
- Find the difference: 120 − 90 = 30.
- Divide by the original price: 30 ÷ 120 = 0.25.
- Multiply by 100: 0.25 × 100 = 25%.
The sale represents a 25% discount off the original price.
