What is X% of Y?
Find a percentage amount, such as 15% of 240.
%×
Result—
Formula: percentage ÷ 100 × number
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Percentage Calculator
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X is what % of Y?
Turn two values into a percentage ratio.
÷= %
Percentage—
Formula: first number ÷ second number × 100
Percentage change
Measure the increase or decrease from an old value.
→%
Change—
Formula: (new − old) ÷ |old| × 100
How to choose the right percentage formula
Use “What is X% of Y?” when the percentage and base are known: 15% of 240 is 0.15 × 240 = 36. Use “X is what % of Y?” when comparing a part with a total: 45 out of 60 is 45 ÷ 60 × 100 = 75%. Use percentage change when comparing an old value with a new value: a rise from 80 to 100 is (100 − 80) ÷ 80 × 100 = 25%.
Percentage points are different
If a rate moves from 20% to 25%, the change is 5 percentage points, but the relative percentage increase is 25%. State which measure you mean when comparing interest rates, survey shares, margins or conversion rates.
Common mistakes
- Choose the original or reference value as the denominator.
- A fall from 100 to 80 is 20%, but returning from 80 to 100 requires a 25% increase.
- Percentage change is undefined when the original value is zero; describe the absolute change instead.
- Round only the displayed answer when possible so intermediate rounding does not compound.