Percentage Calculator
1. What is X% of Y?
2. X is what percent of Y?
3. Percentage change from X to Y
How this percentage calculator works
This tool performs the three most common percentage calculations: finding a percentage of a number, determining what percentage one number is of another, and computing the percentage change between two values. Each mini-calculator is independent and updates instantly.
1. Percentage of a number
Result = (percent ÷ 100) × value
Example: 15% of 200 = 0.15 × 200 = 30. Convert the percentage to a decimal by dividing by 100, then multiply by the base value.
2. X is what percent of Y
Result = (part ÷ whole) × 100
Example: 30 is what percent of 150? → (30 ÷ 150) × 100 = 20%. This is the inverse of the first calculation — useful for test scores, discounts, and proportions.
3. Percentage change
Result = ((new − original) ÷ |original|) × 100
A positive result means growth (shown in green); a negative result means decline (shown in red). Example: going from 100 to 125 is a +25% change. If the original value is zero, the result is undefined because division by zero is impossible.
Percentage change vs. percentage difference
Percentage change has a clear base — the original value — so it tracks movement over time. Percentage difference is used when neither value is a starting point; it averages the two values as the denominator: |a − b| ÷ ((a + b) ÷ 2) × 100.