Math

Percentage Calculator

Find a percent of a number, reverse percentages, and percent change.

What is P% of X?

Percent (P)

Of value (X)

Result

X is what % of Y?

Part (X)

Whole (Y)

Result

Percent change from A to B

From (A)

To (B)

Change

How it works

Percentages compare a part to a whole on a scale of 100. This tool covers three common percentage problems.

What is P% of X? Multiply the fraction of 100 by X.

\[ \frac{P}{100} \times X \]
X is what percent of Y? Divide the part by the whole, then scale to 100.

\[ \frac{X}{Y} \times 100 \]
Percent change from A to B measures how much the value grew or shrank relative to the starting amount.

\[ \frac{B - A}{A} \times 100 \]

Reference → Tutorial: How to Calculate a Percentage → Formula sheet: Percentage Triad →

Worked example

What is 15% of 80? (15/100)×80 = 12. 12 is what percent of 80? (12/80)×100 = 15%. Percent change from 80 to 92: (92−80)/80×100 = 15% increase.

\[ 0.15\times 80=12;\quad \frac{12}{80}\times 100=15\% \]

FAQ

Why does percent change use the starting value in the denominator?

Percent change measures relative movement from A to B, so the baseline is A. Using B (or an average) answers a different question and will not match this calculator.

Can I reverse a percentage increase?

A 15% increase followed by a 15% decrease does not return to the original: 80→92, then 92×0.85=78.2. Undo increases with division by (1 + p/100), not another equal-percent decrease.

Sources

https://en.wikipedia.org/wiki/Percentage

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