Three percentage calculators in one. Calculate X% of Y, find what percentage X is of Y, and calculate percentage change — with formulas shown step by step.
To calculate X% of Y, multiply Y by X and divide by 100. For example, 15% of 200 = 200 × 15 ÷ 100 = 30. This is the most common percentage calculation, used for calculating tips, discounts, taxes, and grades.
The word "percent" literally means "per hundred." So 15% means 15 per 100, or 15/100 = 0.15. Multiplying any number by 0.15 gives you 15% of that number. This calculator performs this calculation instantly as you type.
To find what percentage X is of Y, divide X by Y and multiply by 100. For example, 30 is what % of 200? Answer: (30 ÷ 200) × 100 = 15%.
This calculation is used for test scores (you got 42 out of 50 = 84%), sales conversion rates, completion percentages, and market share calculations. The formula works for any two numbers, and the result tells you the relative proportion as a percentage.
Percentage change = ((New Value − Old Value) ÷ Old Value) × 100. A positive result means increase, negative means decrease. From 200 to 250 = +25% increase. From 200 to 150 = −25% decrease.
This is widely used in finance (stock price changes, revenue growth), economics (inflation, GDP), health (weight change), and everyday life (price comparisons). Note that percentage increase and decrease are not symmetric: a 50% increase followed by a 50% decrease does not return to the original value (100 → 150 → 75).
Percentage calculations come in three fundamental types: finding the percentage of a number, finding what percentage one number is of another, and finding the original number from a percentage.
You can calculate most percentages in your head using a few simple shortcuts based on the commutative property: X% of Y = Y% of X.
This means 8% of 50 = 50% of 8 = 4. Much easier! Other shortcuts:
10%: Move the decimal left one place. 10% of $85 = $8.50
1%: Move the decimal left two places. 1% of $85 = $0.85
5%: Half of 10%. 5% of $85 = $4.25
15%: 10% + 5%. 15% of $85 = $8.50 + $4.25 = $12.75
20%: Double 10%. 20% of $85 = $17.00
25%: Divide by 4. 25% of $85 = $21.25
33%: Divide by 3. 33% of $85 ≈ $28.33
75%: 50% + 25%, or subtract 25% from the whole. 75% of $85 = $63.75
For any percentage: break it into parts. 37% = 30% + 7% = 3 × 10% + 7 × 1%. For $85: 3 × $8.50 + 7 × $0.85 = $25.50 + $5.95 = $31.45.
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Note: Percentage calculations are mathematical operations and are universally applicable. Results are displayed with up to 4 decimal places for precision. For financial calculations, always round to 2 decimal places as appropriate for your currency.
Percentages are used everywhere: grades, taxes, discounts, interest rates, statistics, tips, and data analysis. Understanding how to calculate them quickly is one of the most practical math skills. This calculator handles three common scenarios: finding a percentage of a number, determining what percentage one number is of another, and calculating percentage change.
What is X% of Y? → Y × X ÷ 100. Example: 25% of 80 = 80 × 25 ÷ 100 = 20. X is what % of Y? → (X ÷ Y) × 100. Example: 20 is what % of 80? = (20 ÷ 80) × 100 = 25%. Percentage change from X to Y: → ((Y − X) ÷ X) × 100. Example: from 80 to 100 = ((100-80) ÷ 80) × 100 = +25%.
10% = move decimal left one place. 20% = 10% × 2. 25% = divide by 4. 50% = divide by 2. 75% = subtract 25% from the whole. 1% = move decimal left two places. 33% ≈ divide by 3. These shortcuts let you calculate tips, discounts, and estimates instantly without any tools.