Percentage CalculatorFree online math calculator — instant results, no sign-up
Percent of a number, what percent, and percent change.
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How the result changes with value a
Each row below was calculated with this tool, keeping every other input at its default and changing only value a from half to one and a half times the default value. Use it to see how sensitive the answer is before you enter your own numbers.
| Value A | A% of B | A is what % of B | % change A → B |
|---|---|---|---|
| 10 | 15 | 6.67% | 1,400% |
| 15 | 22.5 | 10% | 900% |
| 20 (default) | 30 | 13.33% | 650% |
| 25 | 37.5 | 16.67% | 500% |
| 30 | 45 | 20% | 400% |
About the Percentage Calculator
This calculator computes four common percentage metrics between two values: finding a percentage of a quantity, determining what percentage one number represents of another, the percentage change from the first value to the second, and the symmetric percentage difference between both values. It is designed for students, shoppers, financial analysts, and anyone comparing numerical data.
- Value A
- The first number, acting as the percentage rate, initial amount, or first comparison value (default: 20).
- Value B
- The second number, acting as the base quantity, final amount, or second comparison value (default: 150).
Formula and method
A% of B = (A / 100) × B A is what % of B = (A / B) × 100 % change A → B = ((B − A) / |A|) × 100 % difference = (|A − B| / ((A + B) / 2)) × 100
- AValue A (first input value)
- BValue B (second input value)
- |A|Absolute value of Value A
- |A − B|Absolute difference between Value A and Value B
The tool evaluates all four expressions simultaneously using floating-point arithmetic. Percent change divides the difference by the absolute value of A to handle negative starting points, while percent difference divides the absolute difference by the average of A and B.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Value A20
- Value B150
Results
- A% of B30
- A is what % of B13.33%
- % change A → B650%
- % difference152.94%
How to use the Percentage Calculator
- 1Multiply B by A divided by 100 to determine A percent of B.
- 2Divide A by B and multiply by 100 to find what proportion A is of B.
- 3Subtract A from B, divide the result by the absolute value of A, and multiply by 100 to get percent change from A to B.
- 4Take the absolute difference between A and B, divide it by the midpoint (A + B) / 2, and multiply by 100 to get percent difference.
Reading your result
A positive percent change indicates growth from A to B, while a negative value signifies a decrease. Percent difference is always non-negative and measures relative variation between two numbers without treating either as the baseline.
Limitations
The formulas produce undefined or infinite results if Value B is zero (for 'A is what % of B'), if Value A is zero (for percent change), or if A and B sum to zero (for percent difference). It assumes linear relative comparison and does not model compounding, inflation, or weighted averages.
Common questions
What is the difference between percent change and percent difference?+
Percent change assumes an initial state (A) and a final state (B), measuring directional growth or decline relative to A. Percent difference is directionless and compares two measurements against their average.
Why is percent change divided by the absolute value of A?+
Dividing by |A| ensures that an increase (where B > A) always results in a positive percentage change, even when starting from a negative value.
What happens if Value B is zero?+
Calculating what percentage A is of B involves dividing by B. If B is zero, the mathematical operation results in division by zero.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
Further reading
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Results are estimates for informational purposes and are not financial, medical or legal advice.