How to use this calculator
Choose the question you want to answer. “Percent of a number” finds a part. “What percent?” compares a part with a whole. “Percentage change” measures an increase or decrease relative to a positive original value.
The formula
Part = base × percentage ÷ 100. Share = part ÷ whole × 100%. Change = (new − original) ÷ original × 100%.
A worked example
15% of 200 is 200 × 15 ÷ 100 = 30. Separately, 30 out of 120 is 25%. A change from 80 to 100 is an increase of 25%, with an absolute change of +20.
What to keep in mind
- The whole cannot be zero when finding a share. Negative parts and nonzero negative wholes are accepted.
- For percentage change, the original value must be greater than zero and the new value must be zero or positive.
- Moving from 20% to 30% is a 50% relative increase and a rise of 10 percentage points.
Formula v1.0.0 · Updated November 6, 2026 · Results: up to 4 decimal places, rounded half up. Very small nonzero values use scientific notation.