Percentage Calculator
Calculate percentages with four different modes: find a percentage of a number, find what percent one number is of another, find percentage change between values, and find original values from percentages. Visual bars, formulas, and quick reference tables included.
How to Use This Calculator
- Select a calculation mode using the tabs below
- Enter the required values for your chosen mode
- Results update instantly as you type
- Click Calculate or press Enter for full results
- Share or bookmark your results - the URL saves your inputs!
Calculation Mode
What is X% of Y?
📊 Understanding Percentages
A percentage is a number expressed as a fraction of 100. The word comes from Latin "per centum" meaning "by the hundred." Percentages are used everywhere: discounts, taxes, tips, grades, statistics, and financial calculations.
🧮 Common Percentage Formulas
- X% of Y: (X / 100) × Y
- X is what % of Y: (X / Y) × 100
- % Change: ((New - Old) / Old) × 100
- Increase by X%: Value × (1 + X/100)
- Decrease by X%: Value × (1 - X/100)
💡 Quick Mental Math Tips
- 10% of anything: Move the decimal one place left (10% of 250 = 25)
- 5%: Find 10% then divide by 2
- 15%: Find 10% then add half of it (good for tips!)
- 20%: Find 10% then double it
- 25%: Divide by 4
- 50%: Divide by 2
🔗 Save & Share Your Calculation
Your inputs are automatically saved in the URL. You can bookmark this page to save your calculation, or use the Share button to send it to others. When you return or share the link, all values will be restored automatically.
Frequently Asked Questions
How do you calculate a percentage of a number?
Multiply the number by the percentage as a decimal. 20% of 150 is 150 × 0.20 = 30. To find what percent one number is of another, divide and multiply by 100.
How do I calculate percentage increase or decrease?
Percent change = (new − old) ÷ old × 100. If a price rises from $80 to $100, that's (100 − 80) ÷ 80 × 100 = 25% increase.
What is X as a percentage of Y?
Divide X by Y and multiply by 100. For example, 45 out of 60 is 45 ÷ 60 × 100 = 75%.
How do I add or subtract a percentage from a number?
To add 15% to 200: 200 × 1.15 = 230. To subtract 15%: 200 × 0.85 = 170. Multiply by (1 + rate) to add or (1 − rate) to subtract.