How to use it
- Pick the row that matches your question.
- Fill in the two boxes on that row.
- The answer updates as you type.
How it works
All three rows come down to one idea: a percentage is a fraction of 100. “X% of Y” is Y × X ÷ 100. “X is what percent of Y” is X ÷ Y × 100. Percent change compares the difference with the starting value, which is the part people most often get backwards.
Worked example
A price goes from 80 to 92. The change is (92 − 80) ÷ 80 × 100 = +15%. Now it drops back from 92 to 80: (80 − 92) ÷ 92 × 100 = −13.04%. Same 12-unit gap, different percentage, because the starting point changed.
Assumptions and limits
- You cannot work out a percent change from zero, so the calculator shows an error rather than a made-up number.
- “Percentage points” are not percents: a rate moving from 4% to 5% is up 1 point, or 25%.
Frequently asked questions
How do I calculate 15% of 80?
Multiply 80 by 15 and divide by 100. The result is 12.
How is percent change calculated?
Subtract the old value from the new value, divide by the old value and multiply by 100. A negative result is a decrease.
Is a 50% increase followed by a 50% decrease the same value?
No. 100 becomes 150, and 50% off 150 is 75. Percentages apply to the current value, not the original one.