Percentage calculator
Enter a part and a total to get the exact percentage instantly.
Percentage calculator: %, increases and discounts
This calculator handles the most common percentage tasks: X% of a number, what percentage one number is of another, and the percentage increase or decrease between two values. Instantly, in your browser.
Basic formulas
To find what percentage A is of B: A / B × 100. For the change between a starting and a final value: (final − start) / start × 100.
Percentages with the rule of three
A percentage is a proportion out of 100, so it’s solved with a direct rule of three. For example, 20% of 150: if 100 corresponds to 150, then 20 corresponds to x → x = 20 × 150 / 100 = 30.
Direct rule of three
Two quantities are directly proportional when, as one rises, the other rises by the same factor. Example: if 3 kg of fruit cost £6, how much do 5 kg cost? More kilos, more cost → x = 5 × 6 / 3 = £10.
Inverse rule of three
They are inversely proportional when, as one rises, the other falls. Example: if 4 workers take 6 days for a job, how long do 8 workers take? More workers, fewer days → x = 4 × 6 / 8 = 3 days. In the direct case you cross-multiply; in the inverse case you multiply straight across.
Frequently asked questions
How do I work out 15% of a number? Multiply the number by 0.15 (or by 15 and divide by 100).
How do I find what percentage one number is of another? Divide the number by the total and multiply by 100.
How do I calculate a percentage increase? Subtract the starting value from the final one, divide by the start and multiply by 100.