Percentage Calculator
The three percentage calculations people actually need — results update as you type.
1. What is X% of Y?
2. X is what percent of Y?
3. Percentage change from X to Y
The formulas, for reference
X% of Y = X ÷ 100 × Y · X as a percent of Y = X ÷ Y × 100 · Percent change = (Y − X) ÷ |X| × 100. A positive change means an increase, a negative one a decrease — e.g. going from 80 to 100 is a +25% change, not 20%, because the change is measured against the starting value.
Frequently asked questions
Why is 80 → 100 a 25% increase but 100 → 80 only a 20% decrease?
Percentage change is always relative to the starting point. From 80, the 20-unit rise is 20/80 = 25%. From 100, the 20-unit fall is 20/100 = 20%. Percentages up and down are not symmetric.
Can I use negative numbers?
Yes — useful for financial values like losses or temperature changes. The percent-change formula uses the absolute starting value, as is standard.