Percentage Calculator
Calculate a percentage using the mode that matches your need.
Step by step: 150 × 20 / 100 = 30
How is this result calculated?
This calculator applies one of the following four formulas depending on the selected mode:
- X % of Y:
result = Y × X / 100 - X is what % of Y?:
result = (X / Y) × 100(Y = 0 is rejected, division by zero is impossible) - Add X %:
result = value × (1 + X / 100) - Subtract X %:
result = value × (1 − X / 100)
The result is displayed instantly with every keystroke, along with a step-by-step breakdown using the values actually entered. As long as a field is empty or non-numeric, no result is shown.
Frequently asked questions
What's the difference between "percentage of" and "percentage increase"?+
"X% of Y" calculates a portion of a number (e.g. 20% of 150 = 30, a value in itself). "Add X%" calculates a new value after an increase (e.g. 150 increased by 20% = 180). The first gives a share, the second gives a new total that includes the starting value.
How do you calculate a percentage by hand?+
To find X% of Y, multiply Y by X then divide by 100 (Y × X / 100). To find what percentage X represents of Y, divide X by Y then multiply by 100 ((X / Y) × 100).
Why do we divide by 100 in percentage calculations?+
A percentage expresses a proportion out of 100 ("per cent"). Dividing by 100 converts the displayed number (e.g. 20%) into its real decimal value (0.20), usable in a multiplication.
What happens if Y = 0 in "X is what % of Y?"+
The calculation is impossible: dividing by zero has no defined mathematical result. The calculator shows a clear error message instead of a result, without crashing or displaying an incorrect value.
Does adding X% then removing X% give back the starting value?+
No, and this is a common mistake. Adding 20% to 150 gives 180, then removing 20% from 180 gives 144, not 150. The reason: the second percentage applies to a different base (180, not 150). The two operations are only symmetric if they apply to the same reference value.