Percentage Calculator
The Percentage Calculator handles three common percentage questions: what a percentage of a number is, what percent one number is of another, and the percentage change between two values. Percentage change is always calculated against the original (starting) value, not the new one — so a change from 80 to 40 is a 50% decrease, but reversing it, 40 back to 80, is a 100% increase, not another 50%, because the denominator shifted. That asymmetry also caps a decrease at −100% (dropping to zero) while an increase has no ceiling — going from 10 to 100 is a 900% increase. The "is what percent of" and "percentage change" modes require a nonzero denominator and will show an error if you enter 0 as the "of" or "original" value, since dividing by zero has no defined percentage.
How This Tool Works
Choose which type of percentage question you have, enter your numbers, and get an instant result.
Formula & Method
What is X% of Y = (X ÷ 100) × Y. X is what percent of Y = (X ÷ Y) × 100. Percentage change = ((new − original) ÷ original) × 100.
Example Calculation
What is 15% of 340? (15 ÷ 100) × 340 = 0.15 × 340 = 51. Separately, 36 is what percent of 240? (36 ÷ 240) × 100 = 0.15 × 100 = 15%. And a price that rises from $80 to $92: (92 − 80) ÷ 80 × 100 = 12 ÷ 80 × 100 = 15% increase. All three questions land on the same 15% relationship, just approached from different directions.
Frequently Asked Questions
What's the formula for percentage change?+
Percentage change = ((new value − original value) ÷ original value) × 100. A positive result is an increase; a negative result is a decrease.
How do I find what percent one number is of another?+
Divide the part by the whole and multiply by 100. For example, 30 is 20% of 150 because 30 ÷ 150 × 100 = 20.
Can percentage change be more than 100%?+
Yes — if a value more than doubles, the percentage increase will exceed 100%. For example, going from 50 to 150 is a 200% increase.
Why does going from 40 back to 80 show 100%, not 50%, even though it undoes an 80-to-40 change?+
Percentage change is always measured against the starting value. 80 to 40 is a 50% decrease because (40 − 80) ÷ 80 = −50%. Reversing it, 40 to 80, is measured against 40 instead: (80 − 40) ÷ 40 = +100%. The base changes between the two directions, so the percentages aren't symmetric — that's expected, not a bug.
What happens if I enter 0 for the 'of' or 'original' value?+
The calculator shows an error instead of a result, since dividing by zero has no defined percentage. This applies to the 'X is what percent of Y' and 'percentage change' modes. The 'what is X% of Y' mode is the exception — it allows Y to be 0 and simply returns 0.
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<a href="https://everyfix.net/tools/percentage-calculator/">Percentage Calculator</a> by <a href="https://everyfix.net">EveryFix</a>Related Tools
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