Percentage Calculator
Percent of a number, X is what % of Y, percentage change, difference and reverse percentages, with the working shown step by step.
Key facts
- X% of Y = X ÷ 100 × Y, so 20% of 150 is 30.
What is % of ?
% of a number
30
20% of 150 is 30
How this works: Method, Checked against 13 worked examples,
How this works
Method
X% of Y is X ÷ 100 × Y, and X as a percent of Y is X ÷ Y × 100. Percentage change is (new − original) ÷ original × 100, percentage difference divides the gap by the average of the two values, and a reverse percentage finds the original as final ÷ (1 ± % ÷ 100). The question pages work in exact fractions and round only the answer you see.
How it’s tested
13 worked examples for this page are checked by automated tests before every release: given the inputs, the tool must show the expected answer.
Changes
- Added eight pages for common questions, from percent of a number to percent error and reverse percentages, each with its own method, examples and table.
- Added key facts with a worked example of each formula.
- Redesigned: type the numbers straight into a sentence, with bars on one scale that picture the answer.
- Results now update as you type, with no Calculate button.
- First published.
All 8 percentage calculators
Parts of a whole · Increases and decreases · Comparing two values
Frequently Asked Questions
How do you calculate percentage manually?
To calculate percentage manually, use the formula: (Part ÷ Whole) × 100. For example, to find what percentage 25 is of 100: (25 ÷ 100) × 100 = 25%. For percentage of a number: (Percentage ÷ 100) × Number. For example, 20% of 150 = (20 ÷ 100) × 150 = 30.
What is the fastest way to calculate percentage?
The fastest way is using an online percentage calculator like this one! For mental math, memorize common percentages: 10% (move decimal one place), 25% (divide by 4), 50% (divide by 2), 75% (divide by 4 then multiply by 3). For 20% of 80: 10% is 8, so 20% is 16.
How do you calculate percentage increase?
Percentage Increase = ((New Value - Original Value) ÷ Original Value) × 100. For example, if a price increased from $50 to $65: ((65 - 50) ÷ 50) × 100 = (15 ÷ 50) × 100 = 30%. The price increased by 30%.
How do you calculate reverse percentage?
Reverse percentage finds the original value before a percentage change. For increase: Original = Final ÷ (1 + Percentage/100). For decrease: Original = Final ÷ (1 - Percentage/100). Example: A product costs $120 after 20% VAT. Original price = 120 ÷ 1.20 = $100.
Why is percentage important in business?
Percentages are crucial in business for profit margins, discounts, growth rates, and performance metrics. They provide a standardized way to compare values regardless of scale. For example, a 20% profit margin means $20 profit for every $100 revenue, making it easy to compare businesses of different sizes.
What is the difference between percentage increase and decrease?
Percentage increase measures growth: (New > Original). Percentage decrease measures reduction: (New < Original). Both use the same formula structure but give positive or negative results. For example, 100 increased to 120 is +20% increase. 100 decreased to 80 is -20% decrease (or 20% decrease).