Three questions that sound similar

“What is 15% of 240?” asks for a portion: divide 15 by 100 and multiply by 240 to get 36. “36 is what percentage of 240?” asks for a share: divide 36 by 240 and multiply by 100 to get 15%. A percentage change compares a new value with a starting value. Moving from 80 to 100 is a 25% increase because the increase of 20 is compared with the original 80.

The starting value matters

Going from 80 to 100 is a 25% increase, but going back from 100 to 80 is a 20% decrease. The base has changed. For ordinary positive starting values, percentage change is (new − original) ÷ original × 100. For a negative starting value, this calculator uses the absolute original value as the denominator and shows that choice in the formula. Interpret changes around negative values carefully.

What zero and rounding mean

A total of zero cannot be used to calculate a share, and a starting value of zero cannot be used for percentage change: both would require division by zero. A zero percent portion is valid and gives zero. Results display up to eight decimal places. Calculations use normal browser floating-point numbers, so this tool is a practical arithmetic helper rather than a replacement for exact decimal accounting.

Worked examples

Question	Calculation	Answer
15% of 240	15 ÷ 100 × 240	36
Change from 80 to 100	(100 − 80) ÷ 80 × 100	+25%

Good questions.

What is a percentage point?

A change from 10% to 15% is an increase of 5 percentage points. Relative to the original 10%, it is a 50% increase. These are different comparisons.

Can I enter decimal percentages?

Yes. For example, 12.5% of 80 is 10. Use a decimal point rather than a comma in number fields.

Why can I not calculate a change from zero?

Percentage change divides by the starting value. Division by zero is undefined. Describe the absolute change instead.

Updated 5 November 2026 · Methods & corrections

Percentage calculator