Three Common Percentage Questions
1. What is X% of Y?
Result = Y × (X / 100)
2. X is what percent of Y?
Percent = (X / Y) × 100
3. Percentage change from A to B
Change % = ((B − A) / A) × 100
Increase when B > A; decrease when B < A.
Percent Increase vs Decrease
Increase by p%:
New = Old × (1 + p/100)
Decrease by p%:
New = Old × (1 − p/100)
Trap: A 50% increase then 50% decrease does not return to start:
100 → 150 → 75
The base changes each step.
Percentage Points vs Percent
Percentage points are absolute differences in rates: going from 3% to 5% is 2 percentage points, not 2 percent increase of the rate.
Confusing the two causes major errors in finance and news.
How to Use This Percentage Calculator
Choose the mode: of, is what % of, or change. Enter values — the tool handles the algebra so you avoid sign and order mistakes.