How to use Percentage Calculator
A percentage expresses a quantity per hundred. Choose the calculation mode first: taking 20% of 250 produces 50, while expressing 20 as a percentage of 250 produces 8%. The same two inputs have different meanings in the two modes.
A zero whole cannot be used as the denominator in the second mode. Negative inputs are supported for general arithmetic, but interpret negative percentages carefully in a real-world context.
The formula
A% of B = A × B / 100
A as a percentage of B = A / B × 100
A worked example
Calculation: A% of B · A: 20 · B: 250
20% of 250: 50
Questions about this calculation
Why do the two modes give different results?
One multiplies by a percentage, while the other divides a part by a whole.
Can the whole be zero?
Only in the “A% of B” mode. A ratio with a zero denominator is undefined.
Formula checks: 2026-10-08. Assumptions & corrections.