Everyday math

Turn percentage questions into clear math.

Choose the question you are trying to answer, enter two values, and see both the result and the formula.

The key idea

Percent means “per hundred.” Converting a percentage to a decimal divides it by 100, so 25% becomes 0.25. Finding 25% of 80 is therefore the same as multiplying 0.25 by 80.

Percent of a whole

Divide the part by the whole, then multiply by 100. If 20 of 80 items are selected, 20 / 80 x 100 = 25%.

Percentage change

Subtract the starting value from the ending value, divide by the absolute starting value, then multiply by 100. The starting value is the comparison base.

Percentage points differ

A rate moving from 20% to 25% rises 5 percentage points, but the relative increase is 25% because 5 is one quarter of the original 20.

Worked examples and comparison bases

For “what is 25% of 80,” the answer is 20. For “20 is what percent of 80,” the answer is 25%. For a change from 80 to 100, the increase is 25% because the original 80 is the comparison base.

When comparing rates, separate percentage points from percent change. A move from 20% to 25% is a 5-percentage-point increase and a 25% relative increase.

Assumptions and limits: this calculator performs general arithmetic. Rounding, measurement precision, negative values, and the meaning of the comparison base can affect how a percentage should be interpreted.

Method reviewed September 29, 2026.

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Turn percentage questions into clear math.

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