Percentage Calculator
Work out a percentage of a value, what percentage one number is of another, or the percentage increase or decrease between two figures.
Formula and method
Percentage of a value: (percentage ÷ 100) × value.
Part as a percentage of a whole: (part ÷ whole) × 100. Undefined when the whole is zero.
Percentage change: ((new − original) ÷ original) × 100. Undefined when the original value is zero.
All arithmetic is carried out at full precision; only the displayed figures are rounded.
Worked example
A supplier quotes €50 and offers 20% off for early settlement.
20% of 50 = (20 ÷ 100) × 50 = 10, so the reduction is €10.
Reversing it: from 80 to 100 is ((100 − 80) ÷ 80) × 100 = 25% increase, while 100 to 80 is a 20% decrease. The two percentages differ because the base changes.
FAQ
Frequently asked questions
How do I work out a percentage of a number?
Divide the percentage by 100 and multiply by the number. 20% of 50 is (20 ÷ 100) × 50 = 10.
How do I work out what percentage one number is of another?
Divide the part by the whole and multiply by 100. 25 out of 50 is (25 ÷ 50) × 100 = 50%.
How is percentage change calculated?
Subtract the original value from the new value, divide by the original value and multiply by 100. From 80 to 100 is ((100 − 80) ÷ 80) × 100 = 25%.
Why does the calculator refuse a starting value of zero?
Percentage change and percentage-of-a-whole both divide by the original value. Dividing by zero has no defined answer, so the calculator reports that instead of showing an infinite result.
Can I use negative numbers and decimals?
Yes. Both are accepted and the underlying arithmetic keeps full precision; only the displayed figures are rounded.
More free tools