Percentage Calculator
Calculate percentages quickly and easily
What is Percentage Calculator?
A percentage calculator is a mathematical tool that handles the three most common percentage problems: finding what percentage one number is of another, calculating a percentage of a given number, and determining what a number is if you know a percentage of it. Percentages are used in virtually every area of daily life — shopping discounts, tax calculations, tip amounts, exam scores, interest rates, and statistical data all rely on percentage arithmetic.
The word "percentage" comes from the Latin "per centum" — meaning "by the hundred." A percentage is simply a ratio expressed as a fraction of 100. When a store advertises "30% off," it means 30 out of every 100 units of the original price is deducted. When a bank quotes a 7.5% annual interest rate, it means you earn or pay 7.5 for every 100 you deposit or borrow.
Altairys's Percentage Calculator handles four types of calculations: (1) X% of Y (e.g., 20% of 150 = 30); (2) X is what % of Y (e.g., 30 is what % of 150 = 20%); (3) Percentage change from X to Y (increase or decrease); (4) X is Y% — find the original value. All calculations happen instantly as you type, with clear step-by-step explanations so you understand the maths, not just the answer.
How to Use Percentage Calculator
- Choose calculation type
Select from: percentage of a number, what percentage, percentage change, or find original value.
- Enter your numbers
Type the values into the input fields — results update instantly as you type.
- Read the result
The answer appears immediately with a clear breakdown of the calculation.
- Copy the answer
Copy the result to clipboard for use in spreadsheets, reports, or messages.
Key Benefits
Results calculate as you type — no need to press enter or click a button.
See the formula and working behind each calculation, not just the final number.
Covers all four common percentage calculation types in one tool.
Useful for shopping, finance, academics, cooking, health, and business.
Frequently Asked Questions
Multiply the number by the percentage and divide by 100. For example, 15% of 200 = (15 × 200) / 100 = 30. Our tool does this automatically.
Subtract the old value from the new value, divide by the old value, and multiply by 100. For example, from 80 to 100: ((100 - 80) / 80) × 100 = 25% increase.
A percentage point is an absolute difference between two percentages. If interest rises from 3% to 5%, that is a 2 percentage point increase but a 66.7% relative increase.
If the discounted price is P and the discount was D%, the original price = P / (1 - D/100). For example, if 80 is 20% off: 80 / 0.8 = 100.