Percentage Calculator
This percentage calculator handles the three everyday percentage questions in one place. Switch the mode to find a percentage of a number, to express one number as a percentage of another, or to measure the percent change between a before and after figure. It is the tool you reach for when working out a grade, a tip share, a survey result, or how much a price moved — anything where the word “percent” appears but the exact arithmetic is easy to fumble in your head.
Calculate
Default result: 16.00
Percentage Calculator · Result
calculators.dev
Result
of × 20 × 80 × 16 × 80 × 80 × 100
Reviewed by the calculators.dev team · Last updated 2026-06-23
How to calculate
Choose a mode from the dropdown, then enter the two numbers it asks for. For “X% of a number”, type the percentage and the number — 20% of 80 multiplies 80 by 0.2 to give 16. For “X is what percent of Y”, divide the part by the whole and multiply by 100, so 16 out of 80 is 20%. For percent change, subtract the original from the new value, divide by the original, and multiply by 100. The answer updates live as you type, so you can try a few numbers without clearing the form.
Percent of a number: result = (percent ÷ 100) × number. Ratio as a percent: result = (part ÷ whole) × 100. Percent change: result = ((new − old) ÷ old) × 100. In every case the “100” converts between a plain ratio and a percentage — a percent is just a fraction out of one hundred.
Example calculation
In the default mode the calculator finds 20% of 80. It multiplies 80 by 20/100, which is 0.2, giving 16. So 20% of 80 is 16 — the same as taking a fifth of the number.
- result
- 16
Assumptions
- A percentage above 100% is allowed and meaningful — 150% of 40 is 60, because percentages are not capped at the whole.
- The ratio and change modes divide by the second number, so a whole or original value of zero is rejected rather than shown as an infinite or undefined result.
- Results are displayed rounded for readability while the underlying calculation keeps full precision.
Common mistakes
- Reading “20% of 80” as “80% of 20” — the two happen to give the same answer here, but swapping the percent and the number is wrong in general.
- Dividing by the new value instead of the original when measuring change, which understates a rise and overstates a fall.
- Moving the decimal point the wrong way: 5% is 0.05, not 0.5, so a percentage entered as a whole number must be divided by 100 before multiplying.
Frequently asked questions
How do I find a percentage of a number?
Divide the percentage by 100 and multiply by the number. For 20% of 80, that is 0.2 × 80 = 16.
How do I work out what percent one number is of another?
Divide the part by the whole and multiply by 100. 16 out of 80 is (16 ÷ 80) × 100 = 20%.
Can a percentage be more than 100%?
Yes. A percentage simply scales a number, so 150% of 40 is 60. Values over 100% describe something larger than the original whole.
Why is the original value not allowed to be zero?
The ratio and change modes divide by it, and division by zero has no defined answer, so the calculator asks for a non-zero figure instead of returning a broken result.